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  • Leggett-Garg K3 quantity discriminates between Dirac and Majorana neutrinos
    Phys.Rev. D96 (2017) 076008

    by: Richter, Monika (Silesia U.) et al.

    The K3 quantity, introduced in a context of the Leggett-Garg inequality violation, is studied for the neutrino oscillations in matter with a phenomenologically modeled dissipative environment. It is shown that the K3 function acquires different values depending on whether the neutrino is a Dirac or Majorana particle, provided that there is a dissipative interaction between matter and neutrinos. The difference occurs for various matter densities and can serve as a potential quantifier verifying the neutrino nature. Moreover, working within a phenomenological model one can suggest the values of the matter density and dissipation for which the difference is the most visible. There exist also special conditions in which the violation of the Leggett-Garg inequality, to a different extent for both kinds of neutrino, is observed.

  • Involution symmetries and the PMNS matrix
    Pramana 89 (2017) 63

    by: Pal, PalashB. (IACS, Kolkata) et al.

    C S Lam has suggested that the PMNS matrix (or at least some of its elements) can be predicted by embedding the residual symmetry of the leptonic mass terms into a bigger symmetry. We analyse the possibility that the residual symmetries consist of involution generators only and explore how Lam’s idea can be implemented.

  • Complex scaling and residual flavour symmetry in the neutrino mass matrix
    Pramana 89 (2017) 64

    by: Roy, Probir (CAPSS, Kolkata)

    Using the residual symmetry approach, we propose a complex extension of the scaling ansatz on the neutrino Majorana mass matrix $M_\nu $ which allows a nonzero mass for each of the three light neutrinos as well as a nonvanishing $\theta _{13}$ . Leptonic Dirac CP violation must be maximal while atmospheric neutrino mixing need not be exactly maximal. Each of the two Majorana phases, to be probed by the search for $0\nu \beta \beta $ decay, has to be zero or $\pi $ and a normal neutrino mass hierarchy is allowed.

  • Why PeV scale left–right symmetry is a good thing
    Pramana 89 (2017) 59

    by: Yajnik, UrjitA. (Indian Inst. Tech., Mumbai)

    Left–right symmetric gauge theory presents a minimal paradigm to accommodate massive neutrinos with all the known conserved symmetries duly gauged. The work presented here is based on the argument that the see-saw mechanism does not force the new right-handed symmetry scale to be very high, and as such some of the species from the spectrum of the new gauge and Higgs bosons can have masses within a few orders of magnitude of the TeV scale. The scale of the left–right parity breaking in turn can be sequestered from the Planck scale by supersymmetry. We have studied several formulations of such just beyond Standard Model (JBSM) theories for their consistency with cosmology. Specifically, the need to eliminate phenomenologically undesirable domain walls gives many useful clues. The possibility that the exact left–right symmetry breaks in conjunction with supersymmetry has been explored in the context of gauge mediation, placing restrictions on the available parameter space. Finally, we have also studied a left–right symmetric model in the context of metastable supersymmetric vacua and obtained constraints on the mass scale of right-handed symmetry. In all the cases studied, the mass scale of the right-handed neutrino $M_\mathrm{R}$ remains bounded from above, and in some of the cases the scale $10^9$  GeV favourable for supersymmetric thermal leptogenesis is disallowed. On the other hand, PeV scale remains a viable option, and the results warrant a more detailed study of such models for their observability in collider and astroparticle experiments.

  • Imprint of non-standard interactions on the CP violation measurements at long baseline experiments
    Pramana 89 (2017) 62

    by: Masud, Mehedi (Nehru U.) et al.

    Neutrino oscillations have been firmly established in the past few decades due to a vast variety of experiments and five of the oscillation parameters (three angles and two mass-squared differences) have been measured to varying degrees of precision. Here the focus is on an important parameter entering the oscillation framework – the leptonic CP-violating phase $\delta $ , about which we know very little. We study the consequences of additional CP-conserving and CP-violating parameters in the presence of non-standard neutrino interactions (NSI) on CP-violation studies at the upcoming long baseline experiment, Deep Underground Neutrino Experiment (DUNE) and compare the capabilities of DUNE with other experiments.

  • Neutrino cross-section in ultrahigh energy regime using double asymptotic limit of QCD
    Pramana 89 (2017) 60

    by: Bora, Kalpana (Gauhati U.) et al.

    Studies on neutrino–nucleon ( ${\nu }N$ ) cross-sections have regained interest due to increasing importance of precision measurements, as they are needed as an ingredient in all neutrino experiments. In this work, we use the QCD-inspired double asymptotic limit fit of electron–proton structure function $F_{2}^{ep}$ to low- $ x $ HERA data, to calculate $\nu $ N cross-section for charged current (CC) and neutral current (NC) neutrino interactions in ultrahigh energy (UHE) neutrino energy ( $E_{\nu }$ ) regime ( $10^{9}\, \mathrm {GeV} \le E_{\nu } \le 10^{12}\, \mathrm {GeV} $ ). The form $F_{2}^{ep} \sim x^{-\lambda (Q^{2})}$ , used in our analysis, can be conjectured like a dynamic pomeron (DP)-type behaviour. We also find an analytic form of the total cross-sections, $\sigma _{\mathrm {CC}}^{\nu N}$ and $\sigma _{\mathrm {NC}}^{\nu N}$ , which appear to be of Reggeon exchange type. We also do a comparative analysis of our results with those available in literature. Future measurements will support / confront our predictions.

  • Electric dipole moments with and beyond flavor invariants
    Nucl.Phys. B924 (2017) 417-452

    by: Smith, Christopher (LPSC, Grenoble) et al.

    In this paper, the flavor structure of quark and lepton electric dipole moments in the SM and beyond is investigated using tools inspired from Minimal Flavor Violation. While Jarlskog-like flavor invariants are adequate for estimating CP -violation from closed fermion loops, non-invariant structures arise from rainbow-like processes. Our goal is to systematically construct these latter flavor structures in the quark and lepton sectors, assuming different mechanisms for generating neutrino masses. Numerically, they are found typically much larger, and not necessarily correlated with, Jarlskog-like invariants. Finally, the formalism is adapted to deal with a third class of flavor structures, sensitive to the flavored U(1) phases, and used to study the impact of the strong CP -violating interaction and the interplay between the neutrino Majorana phases and possible baryon and/or lepton number violating interactions.

  • A Unified Model of Quarks and Leptons with a Universal Texture Zero

    by: de Medeiros Varzielas, Ivo (Lisbon, CFTP) et al.

    We show that a universal texture zero in the (1,1) position of all fermionic mass matrices, including heavy right-handed Majorana neutrinos driving a type-I see-saw mechanism, can lead to a viable spectrum of mass, mixing and CP violation for both quarks and leptons, including (but not limited to) three important postdictions: the Cabibbo angle, the charged lepton masses, and the leptonic `reactor' angle. We model this texture zero with a non-Abelian discrete family symmetry that can easily be embedded in a grand unified framework, and discuss the details of the phenomenology after electroweak and family symmetry breaking. We provide an explicit numerical fit to the available data and obtain excellent agreement with the 18 observables in the charged fermion and neutrino sectors with just 9 free parameters. We further show that the vacua of our new scalar familon fields are readily aligned along desired directions in family space, and also demonstrate discrete gauge anomaly freedom at the relevant scale of our effective theory.

  • Neutrinoless double beta decay in effective field theory: the light Majorana neutrino exchange mechanism

    by: Cirigliano, V.
    We present the first chiral effective theory derivation of the neutrinoless double beta-decay $nn\rightarrow pp$ potential induced by light Majorana neutrino exchange. The effective-field-theory framework has allowed us to identify and parameterize short- and long-range contributions previously missed in the literature. These contributions can not be absorbed into parameterizations of the single nucleon form factors. Starting from the quark and gluon level, we perform the matching onto chiral effective field theory and subsequently onto the nuclear potential. To derive the nuclear potential mediating neutrinoless double beta-decay, the hard, soft and potential neutrino modes must be integrated out. This is performed through next-to-next-to-leading order in the chiral power counting, in both the Weinberg and pionless schemes. At next-to-next-to-leading order, the amplitude receives additional contributions from the exchange of ultrasoft neutrinos, which can be expressed in terms of nuclear matrix elements of the weak current and excitation energies of the intermediate nucleus. These quantities also control the two-neutrino double beta-decay amplitude. Finally, we outline strategies to determine the low-energy constants that appear in the potentials, by relating them to electromagnetic couplings and/or by matching to lattice QCD calculations.

  • Right-handed Neutrino Dark Matter in a U(1) Extension of the Standard Model

    by: Cox, Peter
    We consider minimal $U(1)$ extensions of the Standard Model in which one of the right-handed neutrinos is charged under the new gauge symmetry and plays the role of dark matter. In particular, we perform a detailed phenomenological study for the case of a $U(1)_{(B-L)_3}$ flavoured $B-L$ symmetry. If perturbativity is required up to high-scales, we find an upper bound on the dark matter mass of $m_\chi\lesssim2$ TeV, significantly stronger than that obtained in simplified models. Furthermore, if the $U(1)_{(B-L)_3}$ breaking scalar has significant mixing with the SM Higgs, there are already strong constraints from direct detection. On the other hand, there remains significant viable parameter space in the case of small mixing, which may be probed in the future via LHC $Z^\prime$ searches and indirect detection. We also comment on more general anomaly-free symmetries consistent with a TeV-scale RH neutrino dark matter candidate, and show that if two heavy RH neutrinos for leptogenesis are also required, one is naturally led to a single-parameter class of $U(1)$ symmetries.

  • Exponential Hierarchies from Anderson Localization in Theory Space

    by: Craig, Nathaniel
    We present a new mechanism for generating exponential hierarchies in four-dimensional field theories inspired by Anderson localization in one dimension, exploiting an analogy between the localization of electron energy eigenstates along a one-dimensional disordered wire and the localization of mass eigenstates along a local "theory space" with random mass parameters. Mass eigenstates are localized even at arbitrarily weak disorder, with exponentially suppressed couplings to sites in the theory space. The mechanism is quite general and may be used to exponentially localize fields of any spin. We apply the localization mechanism to two hierarchies in Standard Model parameters --- the smallness of neutrino masses and the ordering of quark masses --- and comment on possible relevance to the electroweak hierarchy problem. This raises the compelling possibility that some of the large hierarchies observed in and beyond the Standard Model may result from disorder, rather than order.

  • Subjecting dark matter candidates to the cluster test

    by: Nieuwenhuizen, Theodorus Maria
    Galaxy clusters, employed by Zwicky to demonstrate the existence of dark matter, pose new stringent tests. If merging clusters demonstrate that dark matter is self-interacting with cross section $\sigma/m\sim 2$ cm$^2$/gr, MACHOs, primordial black holes and light axions that build MACHOs are ruled out as cluster dark matter. Recent strong lensing and X-ray gas data of the quite relaxed and quite spherical cluster A1835 allow to test the cases of dark matter with Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac distribution, next to Navarro-Frenck-White profiles. Fits to all these profiles are formally rejected at over $5\sigma$, except in the fermionic situation. The interpretation in terms of (nearly) Dirac neutrinos with mass of $1.61^{+0.19}_{-0.30}$ eV/$c^2$ is consistent with results on the cluster A1689, with the WMAP, Planck and DES dark matter fractions and with the nondetection of neutrinoless double $\beta$-decay. The case will be tested in the 2018 KATRIN experiment.

  • Study of texture zeros of fermion mass matrices in minimal extended seesaw mechanism and symmetry realization
    Int.J.Mod.Phys. A32 (2017) 1750168

    by: Patgiri, Mahadev (Assam U.) et al.

    In our work, we study the texture zeros of mν in the minimal extended type-I seesaw (MES) with incorporating one extra gauge singlet field “S”. The MES models deal with the Dirac neutrino mass matrix (MD), the right-handed Majorana mass matrix (MR) and the sterile neutrino mass matrix (MS). We carry out the mapping of all possible zero textures of MD, MR and MS for phenomenologically predictive cases having total eight zeros of MD and MR studied in the literature. With this motivation, we consider (a) (4 + 4) scheme, (b) (5 + 3) scheme and (c) (6 + 2) scheme, where the digits of a pair represent the number of zeros of MD and MR, respectively along with the one zero and two zero textures of (MS). There are a large number of possibilities of zeros of fermion mass matrices but the implementation of S3 transformations reduces it to a very minimum number of basic structures. Interestingly out of four allowed one zero textures of mν without sterile neutrino, only three cases (meτ = 0, mμμ = 0 and mττ = 0) are allowed in MES mechanism for the (4 + 4) and (5 + 3) schemes. We find some correlations for different combination of MD, MR and MS on enforcement of zeros. We examined all the correlations under the recent neutrino oscillation data and find that only mττ = 0 survives while both meτ = 0 and mμμ = 0 are ruled out. Interestingly the one zero textures inherently represent the inverted hierarchy of the mass ordering of light neutrinos. No two zero textures of mν survive in MES although there are a number of allowed structures phenomenologically. The allowed texture zeros are finally realized using a discrete Abelian flavor symmetry group Z7 with the extension of standard model to include some scalar fields.

  • Pursuit for optimal baseline for matter nonstandard interactions in long baseline neutrino oscillation experiments

    by: Kärkkäinen, Timo J.
    We investigate the prospects for probing the strength of the possible matter nonstandard neutrino interactions (mNSI) in long baseline neutrino oscillation experiments and the interference of the leptonic CP angle $\delta_{CP}$ with the constraining of the mNSI couplings. The interference is found to be strong in the case of the $\nu_e \leftrightarrow \nu_\mu$ and $\nu_e \leftrightarrow \nu_\tau$ transitions but not significant in the other cases. We use SPS and DUNE setups as benchmarks.

  • The Neutrino Option

    by: Brivio, Ilaria
    We discuss the possibility that the Higgs potential and electroweak scale are generated radiatively in a type-I seesaw scenario. A Higgs potential consistent with experimental constraints can be obtained in this hypothesis for a Majorana mass scale $m_N\sim 10-500$ PeV and with neutrino Yukawa couplings of order $|\omega|\sim 10^{-4.5}-10^{-6}$. Remarkably, neutrino masses and mixings can be simultaneously accommodated within this parameter space. This framework, that ties together Higgs phenomenology, precision top quark mass measurements and neutrino physics, represents an alternative approach to the hierarchy problem, in which the Higgs mass is not stabilized around the TeV scale, but rather determined by radiative corrections at higher energies. Traditional hurdles in overcoming the hierarchy problem are then traded for the new challenge of generating PeV Majorana masses while suppressing the tree-level scalar potential in the UV.

  • A multi-messenger study of the total galactic high-energy neutrino emission

    by: Pagliaroli, G.
    A detailed multi-messenger study of the high-energy emission from the Galactic plane is possible nowadays thanks to the observations provided by gamma and neutrino telescopes and could be mandatory in order to obtain a consistent scenario. We show the potential of this approach by using the total gamma flux from the inner galactic region measured by HESS at $1\,{\rm TeV}$ and in the longitude range $-75^\circ < l < 60^\circ$. By comparing the observational data with the expected diffuse galactic emission, we highlight the existence of an extended hot region of the gamma sky where the cumulative sources contribution dominates over the diffuse component. This region approximately coincides with the portion of the galactic plane from which a $\sim 2 \sigma$ excess of showers is observed in IceCube high energy starting events. In the assumption that hadronic mechanisms are responsible for the observed gamma emission, we estimate the total galactic contribution (i.e. including both diffuse and the source components) to the IceCube neutrino signal as a function of the spectral index and energy cutoff of the sources, taking also into account the upper limit on a galactic component provided by Antares.

  • Neutrino Mass, Leptogenesis, and Dark Matter from The Dark Sector with $U(1)_{D}$

    by: Yang, Wei-Min
    I suggest a new extension of the SM by introducing a dark sector with the local $U(1)_{D}$ symmetry. The particles in the dark sector bring about the new physics beyond the SM. The model can generate the tiny neutrino mass by a hybrid seesaw mechanism, achieve the leptogenesis at the TeV scale, and account for the cold dark matter and the "WIMP Miracle". Finally, it is very feasible to test the model in near future experiments.

  • A non-vanishing neutrino mass and the strong CP problem: A new solution from the perspective of the EW-$\nu_R$ model

    by: Hung, P.Q.
    The EW-$\nu_R$ model was constructed to provide a scenario in which right-handed neutrinos are non-sterile and have masses proportional to the electroweak scale, providing an opportunity to test the seesaw mechanism at the LHC. What was hidden in the model until recently is the chiral symmetry which helps solve the strong CP problem by using it to rotate $\theta_{QCD}$ to zero. It turns out the contribution from the electroweak sector to the effective $\bar{\theta}$ is proportional to the light neutrino masses and is naturally small, satisfying the constraint coming from the present absence of the neutron electric dipole moment, and without the need for an axion. Talk presented at the APS Division of Particles and Fields Meeting (DPF 2017), July 31-August 4, 2017, Fermilab. C170731

  • Neutrino oscillations: the rise of the PMNS paradigm

    by: Giganti, Claudio
    Since the discovery of neutrino oscillations, the experimental progress in the last two decades has been very fast, with the precision measurements of the neutrino squared-mass differences and of the mixing angles, including the last unknown mixing angle $\theta_{13}$. Today a very large set of oscillation results obtained with a variety of experimental configurations and techniques can be interpreted in the framework of three active massive neutrinos, whose mass and flavour eigenstates are related by a 3 $\times$ 3 unitary mixing matrix, the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix, parameterized by three mixing angles $\theta_{12}$, $\theta_{23}$, $\theta_{13}$ and a CP-violating phase $\delta_{CP}$. The additional parameters governing neutrino oscillations are the squared-mass differences $\Delta m^2_{ji}=m^2_j-m^2_i$, where $m_i$ is the mass of the $i$th neutrino mass eigenstate. This review covers the rise of the PMNS three-neutrino mixing paradigm and the current status of the experimental determination of its parameters. The next years will continue to see a rich program of experimental endeavour coming to fruition and addressing the three missing pieces of the puzzle, namely the determination of the octant and precise value of the mixing angle $\theta_{23}$, the unveiling of the neutrino mass ordering (whether $m_1 < m_2 < m_3$ or $m_3 < m_1 < m_2$) and the measurement of the CP-violating phase \dcp.

  • Sensitivity to neutrino decay with atmospheric neutrinos at INO

    by: Choubey, Sandhya
    Sensitivity of the magnetised Iron CALorimeter (ICAL) detector at the proposed India-based Neutrino Observatory (INO) to invisible decay of the mass eigenstate $\nu_3$ using atmospheric neutrinos is explored. A full three-generation analysis including earth matter effects is performed in a framework with both decay and oscillations. The wide energy range and baselines offered by atmospheric neutrinos are shown to be excellent for constraining the $\nu_3$ lifetime. We find that with an exposure of 500 kton-yr the ICAL atmospheric experiment could constrain the $\nu_3$ lifetime to $\tau_3/m_3>1.51\times10^{-10}$ s/eV at the 90\% C.L. This is two orders of magnitude tighter than the bound from MINOS. The effect of invisible decay on the precision measurement of $\theta_{23}$ and $|\Delta{m^2_{32}}|$ is also studied.

  • Neutrino Parameters from Reactor and Accelerator Neutrino Experiments

    by: Lindner, Manfred
    We revisit correlations of neutrino oscillation parameters in reactor and long-baseline neutrino oscillation experiments. A framework based on an effective value of $\theta_{13}$ is presented, which can easily reproduce experimental results. It also clarifies why current and future long-baseline experiments will have less precision on values around $\delta_{CP} = \pm \pi/2$ than on values around $\delta_{CP} = 0$. Optimization potential for the determination of the theoretically very interesting values around $\delta_{CP} = -\pi/2$ is also pointed out, which would require that future runs of accelerator experiments are not equally shared $1:1$ in neutrino and antineutrino modes, but rather $2:1$. Recent hints on the CP phase and the mass ordering are then considered from the point of view that different reactor and long-baseline neutrino experiments provide currently different best-fit values of $\theta_{13}$ and $\theta_{23}$. We point out that the significance of the hints changes for the different available best-fit values.

  • Invoking Chiral Vector Leptoquark to explain LFU violation in B Decays

    by: Chauhan, Bhavesh
    LHCb has recently reported more than $2\sigma$ deviation from the Standard Model prediction in the observable $R_{J/\psi}$. We study this anomaly in the framework of a vector leptoquark along with other lepton flavor universality violating measurements which include $R_{K^{(*)}}$, and $R_{D^{(*)}}$. We show that a chiral vector leptoquark can explain all the aforementioned anomalies consistently while also respecting other experimental constraints.

  • Neutrino oscillation processes in quantum field-theoretical approach

    by: Egorov, Vadim O.
    It is shown that neutrino oscillation processes can be consistently described in the framework of quantum field theory. Namely, the oscillating electron survival probabilities in experiments with neutrino detection by charged-current and neutral-current interactions are calculated in the quantum field-theoretical approach to neutrino oscillations based on a modification of the Feynman propagator. The approach is most similar to the standard Feynman diagram technique in the momentum representation. It is found that the oscillating distance-dependent probabilities of detecting an electron in experiments with neutrino detection by charged-current and neutral-current interactions exactly coincide with the corresponding probabilities calculated in the standard approach.

  • Effect of sterile Neutrinos and Nonstandard Interactions on the Geo-neutrino Flux

    by: Yan, Guanwen
    We calculate the effect of sterile neutrinos and nonstandard neutrino interactions on the flux of active neutrinos from the Earth's crust and mantle taking matter effect into account in both cases. For simple Earth model and using previous emission flux estimates at the source, we find that for reasonable choice of parameters for both the sterile neutrino and nonstandard interaction, the effect on the neutrino flux is a few percent or less.

  • Probing New Physics in Low Energy Solar Neutrino Oscillation Data

    by: Khan, Amir N.
    We explore the effects of nonstandard neutrino interactions in the lower components of the solar neutrino spectrum which are predominant by the vacuum oscillations. The recent measurements of Borexino experiment between 2011 and 2015 provide a clean test to study the nonstandard neutrino interactions at the source (sun) and the at solar detector. In this work, first the possible standard model parameters are estimated from the combined data of the low energy regime and then the nonstandard effects at the source, at the detector, and from the interplay between source and detector parameters are bounded. The same effects are also investigated for the proposed experiments like LENA and Jinpin Neutrino Experiment with their projected sensitivities.

  • Jet substructure shedding light on heavy Majorana neutrinos at the LHC

    by: Das, Arindam
    The existence of tiny neutrino masses and flavor mixings can be explained naturally in various seesaw models, many of which typically having additional Majorana type SM gauge singlet right handed neutrinos ($N$). If they are at around the electroweak scale and furnished with sizeable mixings with light active neutrinos, they can be produced at high energy colliders, such as the Large Hadron Collider (LHC). A characteristic signature would be same sign lepton pairs, violating lepton number, together with light jets -- $pp\to N\ell^{\pm}, \; N\to\ell^{\pm}W^{\mp}, \; W^{\mp}\to jj$. We propose a new search strategy utilising jet substructure techniques, observing that for a heavy right handed neutrino mass $M_N$ much above $M_{W^\pm}$, the two jets coming out of the boosted $W^\pm$ may be interpreted as a single fat-jet ($J$). Hence, the distinguishing signal topology will be $\ell^{\pm}\ell^{\pm} J$. Performing a comprehensive study of the different signal regions along with complete background analysis, in tandem with detector level simulations, we compute statistical significance limits. We find that heavy neutrinos can be explored effectively for mass ranges $300$ GeV $\leq M_N \leq 800$ GeV and different light-heavy neutrino mixing $|V_{\mu N}|^{2}$. At the 13 TeV LHC with 3000 $\mathrm{fb}^{-1}$ integrated luminosity one can competently explore mixing angles much below present LHC limits, and moreover exceed bounds from electroweak precision data.

  • On the Possibility to Determine Neutrino Mass Hierarchy via Supernova Neutrinos with Short-Time Characteristics

    by: Jia, Junji
    In this paper, we investigate whether it is possible to determine the neutrino mass hierarchy via a high-statistics and real-time observation of supernova neutrinos with short-time characteristics. The essential idea is to utilize distinct times-of-flight for different neutrino mass eigenstates from a core-collapse supernova to the Earth, which may significantly change the time distribution of neutrino events in the future huge water-Cherenkov and liquid-scintillator detectors. For illustration, we consider two different scenarios. The first case is the neutronization burst of $\nu^{}_e$ emitted in the first tens of milliseconds of a core-collapse supernova, while the second case is the black hole formation during the accretion phase for which neutrino signals are expected to be abruptly terminated. In the latter scenario, it turns out only when the supernova is at a distance of a few Mpc and the fiducial mass of the detector is at the level of gigaton, might we be able to discriminate between normal and inverted neutrino mass hierarchies. In the former scenario, the probability for such a discrimination is even less due to a poor statistics.

  • Study of rare mesonic decays involving di-neutrinos in their final state

    by: Mir, Azeem
    We have carried out phenomenological implication of R-parity violating ($\NEG% {R}_{p}$) Minimal Supersymmetric Model (MSSM) via analyses of pure leptonic($% M\rightarrow \nu \bar{\nu}$) and semileptonic decays of pseudo-scalar mesons(% $M\rightarrow X\nu \bar{\nu}$). These analyses involve prediction of branching fraction of pure leptonic decays by using experimental limits/bounds derived from the study of semileptonic decays on $\NEG{R}_{p}$ parameters. We have found, in general that $\NEG{R}_{p}$ contribution dominates over the SM contribution i.e., by a factor of $10^{2}$ for the semleptonic decays of $K^{0}$, $10$ for the pure leptonic decays of $K_{L,S}$ , while $10^{2}~$\& $10^{4}$ in case of $B_{s}$ and $B_{d}$ respectively. This demonstrates the role of $\NEG{R}_{p}$ as a viable model for the study of NP contribution in rare decays.

  • Lepton Number Violation, Lepton Flavour Violation and Baryogenesis in Left-Right Symmetric Model
    Phys.Rev. D96 (2017) 075021

    by: Borgohain, Happy
    We did a model independent phenomenological study of baryogenesis via leptogenesis, neutrinoless double beta decay (NDBD) and charged lepton flavour violation (CLFV) in a generic left-right symmetric model (LRSM) where neutrino mass originates from the type I + type II seesaw mechanism. We studied the new physics contributions to NDBD coming from the left-right gauge boson mixing and the heavy neutrino contribution within the framework of LRSM. We have considered the mass of the RH gauge boson to be specifically 5 TeV, 10 TeV and 18 TeV and studied the effects of the new physics contributions on the effective mass and baryogenesis and compared with the current experimental limit. We tried to correlate the cosmological BAU from resonant leptogenesis with the low energy observables, notably, NDBD and LFV with a view to finding a common parameter space where they coexists.

  • Higgs inflation puts lower and upper bounds on tensor-to-scalar ratio and on Higgs-portal-dark-matter mass

    by: Hamada, Yuta
    We find a theoretical lower bound on the tensor-to-scalar ratio $r$ from a premise that extrapolation of the Higgs-field direction plays the role of the inflaton at high scales. We assume that all the non-minimal couplings are not particularly large, $\xi\lesssim 10^2$, so that the renormalizable low-energy effective field theory is reliable up to $10^{17}$ GeV ($\lesssim M_\text{P}/\sqrt{\xi}$). This framework includes the so-called critical Higgs inflation. In our analysis, we take into account the Higgs-portal scalar dark matter and the heavy right-handed neutrinos. The resultant bounds are rather stringent. In particular in the absence of the right-handed neutrinos, namely, when the right-handed-neutrino masses are smaller than $10^{13}$ GeV, the Planck bound $r<0.09$ implies that the dark-matter mass must be smaller than 1.2 TeV. On the other hand, the PandaX-II bound on the dark-matter mass $m_\text{DM}\gtrsim 750$ GeV leads to $r\gtrsim 4\times10^{-3}$. Both are within the range of near-future detection. When we include the right-handed neutrinos of mass $M_\text{R}\sim 10^{14}$ GeV, the allowed region becomes wider, but we still predict $r\gtrsim 10^{-3}$ in the most of the parameter space. The most conservative bound becomes $r>10^{-5}$ if we allow three-parameter tuning of $m_\text{DM}$, $M_\text{R}$, and the top-quark mass.

  • A Portalino to the Dark Sector

    by: Schmaltz, Martin (Boston U.) et al.

    "Portal" models that connect the Standard Model to a Dark Sector allow for a wide variety of scenarios beyond the simplest WIMP models. Kinetic mixing of gauge fields in particular has allowed a broad range of new ideas. However, the models that evade CMB constraints are often non-generic, with new mass scales and operators to split states and suppress indirect detection signals. Models with a "portalino", a neutral fermion that marries a linear combination of a standard model neutrino and dark sector fermion and carries a conserved quantum number, can be simpler. This is especially interesting for interacting dark sectors; then the unmarried linear combination which we identify as the standard model neutrino inherits these interactions too, and provides a new, effective interaction between the dark sector and the standard model. These interactions can be simple $Z'$ type interactions or lepton-flavor changing. Dark matter freezes out into neutrinos, thereby evading CMB constraints, and conventional direct detection signals are largely absent. The model offers different signals, however. The "portalino" mechanism itself predicts small corrections to the standard model neutrino couplings as well as the possibility of discovering the portalino particle in collider experiments. Possible cosmological and astroparticle signatures include monochromatic neutrino signals from annihilation, spectral features in high energy CR neutrinos as well as conventional signals of additional light species and dark matter interactions.

  • Neutrino mass matrices with three or four vanishing cofactors and non diagonal charged lepton sector

    by: Dev, S. (HNB Garhwal U.) et al.

    We investigate the texture structures of lepton mass matrices with four (five) non-zero elements in the charged lepton mass matrix and three (four) vanishing cofactors in the neutrino mass matrix. Using weak basis transformations, all possible textures for three and four vanishing cofactors in $M_{\nu}$ are grouped into 7 classes and predictions for the unknown parameters such as the Dirac CP violating phase and the effective Majorana mass for the phenomenologically allowed textures have been obtained. We, also, illustrate how such texture structures can be realized using discrete Abelian flavor symmetries.

  • Optimizing Higgs factories by modifying the recoil mass

    by: Gu, Jiayin (Beijing, Inst. High Energy Phys.) et al.

    It is difficult to measure the $WW$-fusion Higgs production process ($e^+e^- \to \nu \bar{\nu} h$) at a lepton collider with a center of mass energy of 240-250 GeV due to its small rate and the large background from the Higgsstrahlung process with an invisible $Z$ ($e^+e^- \to hZ,\,Z\to \nu\bar{\nu}$). We construct a modified recoil mass variable, $m^p_{\rm recoil}$, defined using only the 3-momentum of the reconstructed Higgs particle, and show that it can better separate the $WW$-fusion and Higgsstrahlung events than the original recoil mass variable $m_{\rm recoil}$. Consequently, the $m^p_{\rm recoil}$ variable can be used to improve the overall precisions of the extracted Higgs couplings, in both the conventional framework and the effective-field-theory framework. We also explore the application of the $m^p_{\rm recoil}$ variable in the inclusive cross section measurements of the Higgsstrahlung process, while a quantitive analysis is left for future studies.

  • Direct detection signals of dark matter with magnetic dipole moment

    by: Del Nobile, Eugenio (U. Padua, Dept. Phys. Astron.)

    A neutral dark matter (DM) particle with a magnetic dipole moment has a very different direct detection phenomenology with respect to standard candidates. This is due to the peculiar functional form of the differential cross section for scattering with nuclei. Such a candidate could be a bound state of charged particles, as the neutron or an atom, or a fundamental particle coupled to heavier charged states, much like a Dirac neutrino. We analyze here the direct detection signals of DM with magnetic dipole moment, both the recoil rate and its modulation, and show that they are very different from those expected in standard scenarios. For this candidate, contrary to the common lore, the time of maximum signal depends on the recoil energy as well as on the target material. The observation of different modulations by experiments employing different targets would be a strong indication in favor of this type of DM particles.

  • Fast Neutrino Flavor Conversion as Oscillations in a Quartic Potential

    by: Dasgupta, Basudeb (Tata Inst.) et al.

    Neutrinos in dense environments undergo collective pair conversions $\nu_e\bar{\nu}_e \leftrightarrow \nu_x\bar{\nu}_x$, where $x$ is a non-electron flavor, due to forward scattering off each other that may be a crucial ingredient for supernova explosions. Depending on the flavor-dependent local angular distributions of the neutrino fluxes, the conversion rate can be "fast", i.e., of the order $\mu=\sqrt{2}G_F n_\nu$, which can far exceed the usual neutrino oscillation frequency $\omega=\Delta m^2/(2E)$. Until now, this surprising nonlinear phenomenon has only been understood in the linear regime and explored further using numerical experiments. We present an analytical treatment of the simplest system that exhibits fast conversions, and show that the conversion can be understood as the dynamics of a particle rolling down in a quartic potential governed dominantly by $\mu$, but seeded by slower oscillations.

  • Testing NSI suggested by the solar neutrino tension in T2HKK and DUNE

    by: Ghosh, Monojit (Tokyo Metropolitan U.) et al.

    It has been known that a tension between the mass-squared differences obtained from the solar neutrino and KamLAND experiments may be solved by introducing the Non-Standard flavor-dependent Interaction (NSI) in neutrino propagation. We discuss the possibility to test such a hypothesis by the future long baseline neutrino experiments T2HKK and DUNE. Assuming that NSI does not exist, we give the excluded region in the ($\epsilon_D$, $\epsilon_N$)-plane, where $\epsilon_D$ and $\epsilon_N$ are the parameters which appear in the solar neutrino analysis with NSI. It is found that the best-fit value from the solar neutrino and KamLAND data (global analysis) can be tested at more than 10$\sigma$ (3$\sigma$) by the two experiments for most the parameter space.

  • The EPPS16 nuclear PDFs

    by: Eskola, Kari J. (Helsinki Inst. of Phys.) et al.

    We report on EPPS16 - the first analysis of NLO nuclear PDFs where LHC p-Pb data (Z, W, dijets) have been directly used as a constraint. In comparison to our previous fit EPS09, also data from neutrino-nucleus deeply-inelastic scattering and pion-nucleus Drell-Yan process are now included. Much of the theory framework has also been updated from EPS09, including a consistent treatment of heavy quarks in deeply-inelastic scattering. However, the most notable change is that we no longer assume flavour-blind nuclear modifications for valence and sea quarks. This significantly reduces the theoretical bias. All the analysed data are well reproduced and the analysis thereby supports the validity of collinear factorization in high-energy collisions involving heavy nuclei. However, flavour by flavour, the uncertainties are still rather large.

  • Common Origin of Neutrino Mass and Dark Matter from Anomaly Cancellation Requirements of a $U(1)_{B-L}$ Model

    by: Nanda, Dibyendu (Indian Inst. Tech., Guwahati) et al.

    We study a gauged $B-L$ extension of the standard model where the new fermions with fractional $B-L$ charges that play the role of keeping the model anomaly free can also explain the origin of neutrino mass at one loop level as well as dark matter. We discuss two different versions of the model to realise fermion and scalar dark matter, both of which guarantee the dark matter stability by a remnant discrete symmetry to which $U(1)_{B-L}$ gauge symmetry gets spontaneously broken down to. Apart from giving rise to the observed neutrino mass and dark matter abundance, the model also has tantalising signatures at variety of experiments operating at cosmic, intensity and energy frontiers, particularly direct and indirect detection experiments of dark matter, rare decay experiments looking for charged lepton flavour violation as well as collider experiments. The model also predicts vanishing lightest neutrino mass that can be tested at experiments sensitive to the absolute neutrino mass scale.

  • Some Phenomenologies of a Simple Scotogenic Inverse Seesaw Model

    by: Tang, Yi-Lei (Korea Inst. Advanced Study, Seoul)

    In this paper, we discuss and calculate the electroweak parameters $R_l$, $A_l$, and $N_{\nu}^l$ in a model that combine inverse seesaw with the scotogenic model. Dark matter relic density is also considered. Due to the stringent constraint from the ATLAS experimental data, it is difficult to detect the loop effect on $R_l$, $A_l$ in this model considering both the theoretical and future experimental uncertainties. However, $N_{\nu}^l$ can sometimes become large enough for the future experiments to verify.

  • Phenomenology of Majorons

    by: Heeck, Julian (Brussels U.)

    Majorons are the Goldstone bosons associated to lepton number and thus closely connected to Majorana neutrino masses. Couplings to charged fermions arise at one-loop level, including lepton-flavor-violating ones that lead to decays $\ell\to \ell' J$, whereas a coupling to photons is generated at two loops. The typically small couplings make massive majorons a prime candidate for long-lived dark matter. Its signature decay into two mono-energetic neutrinos is potentially detectable for majoron masses above MeV.

  • Possible roles of Peccei-Quinn symmetry in an effective low energy model

    by: Suematsu, Daijiro (Kanazawa U., Inst. Theor. Phys.)

    Strong $CP$ problem is known to be solved by imposing Peccei-Quinn (PQ) symmetry. However, domain wall problem caused by the spontaneous breaking of its remnant discrete subgroup could make models invalid in many cases. We propose a model in which the PQ charge is assigned quarks so as to escape this problem without introducing any extra colored fermions. In the low energy effective model resulting after the PQ symmetry breaking, both the quark mass hierarchy and the CKM mixing could be explained through Froggatt-Nielsen mechanism. If the model is combined with the lepton sector supplemented by an inert doublet scalar and right-handed neutrinos, the effective model reduces to the scotogenic neutrino mass model in which both the origin of neutrino masses and dark matter are closely related. The strong $CP$ problem could be related to the quark mass hierarchy, neutrino masses and dark matter through the PQ symmetry.

  • Freeze-out of baryon number in low-scale leptogenesis

    by: Eijima, S. (EPFL, Lausanne, LPPC) et al.

    Low-scale leptogenesis provides an economic and testable description of the origin of the baryon asymmetry of the Universe. In this scenario, the baryon asymmetry of the Universe is reprocessed from the lepton asymmetry by electroweak sphaleron processes. Provided that sphalerons are fast enough to maintain equilibrium, the values of the baryon and lepton asymmetries are related to each other. Usually, this relation is used to find the value of the baryon asymmetry at the time of the sphaleron freeze-out. To put in other words, the formula which is valid only when the sphalerons are fast, is applied at the moment when they are actually switched off. In this paper, we examine the validity of such a treatment. To this end, we solve the full system of kinetic equations for low-scale leptogenesis. This system includes equations describing the production of the lepton asymmetry in oscillations of right-handed neutrinos, as well as a separate kinetic equation for the baryon asymmetry. We show that for some values of the model parameters, the corrections to the standard approach are sizeable. We also present a feasible improvement to the ordinary procedure, which accounts for these corrections.

  • A Comprehensive Renormalisation Group Analysis of the Littlest Seesaw Model

    by: Geib, Tanja (Munich, Max Planck Inst.) et al.

    We present a comprehensive renormalisation group analysis of the Littlest Seesaw model involving two right-handed neutrinos and a very constrained Dirac neutrino Yukawa coupling matrix. We perform the first $\chi^2$ analysis of the low energy masses and mixing angles, in the presence of renormalisation group corrections, for various right-handed neutrino masses and mass orderings, both with and without supersymmetry. We find that the atmospheric angle, which is predicted to be near maximal in the absence of renormalisation group corrections, may receive significant corrections for some non-supersymmetric cases, bringing it into close agreement with the current best fit value in the first octant. By contrast, in the presence of supersymmetry, the renormalisation group corrections are relatively small, and the prediction of a near maximal atmospheric mixing angle is maintained, for the studied cases. Forthcoming results from T2K and NOvA will decisively test these models at a precision comparable to the renormalisation group corrections we have calculated.

  • Implications of GW related searches for IceCube

    by: de Vries, Krijn D. (Vrije U., Brussels) et al.

    At the beginning of 2016, LIGO reported the first-ever direct detection of gravitational waves. The measured signal was compatible with the merger of two black holes of about 30 solar masses, releasing about 3 solar masses of energy in gravitational waves. We consider the possible neutrino emission from a binary black hole merger relative to the energy released in gravitational waves and investigate the constraints coming from the non-detection of counterpart neutrinos, focusing on IceCube and its energy range. The information from searches for counterpart neutrinos is combined with the diffuse astrophysical neutrino flux in order to put bounds on neutrino emission from binary black hole mergers. Prospects for future LIGO observation runs are shown and compared with model predictions.

  • Cold light dark matter in extended seesaw models

    by: Boulebnane, Sami (Brussels U.) et al.

    We present a thorough discussion of light dark matter produced via freeze-in in two-body decays A -> B DM. If A and B are quasi-degenerate, the dark matter particle has a cold spectrum even for sub-keV masses. We show this explicitly by calculating the transfer function that encodes the impact on structure formation. As examples for this setup we study extended seesaw mechanisms with a spontaneously broken global U(1) symmetry, such as the inverse seesaw. The eV-keV-scale pseudo-Goldstone dark matter particle is then naturally produced cold by the decays of the quasi-degenerate right-handed neutrinos.

  • Calculation of the decay rate of tachyonic neutrinos against charged-lepton-pair and neutrino-pair Cerenkov radiation
    J.Phys. G44 (2017) 105201

    by: Jentschura, Ulrich D. (Missouri U., Rolla) et al.

    We consider in detail the calculation of the decay rate of high-energy superluminal neutrinos against (charged) lepton pair Cerenkov radiation, and neutrino pair Cerenkov radiation, i.e., against the decay channels $\nu \to \nu \,{e}^{+}\,{e}^{-}$ and $\nu \to \nu \,\overline{\nu }\,\nu $. Under the hypothesis of a tachyonic nature of neutrinos, these decay channels put constraints on the lifetime of high-energy neutrinos for terrestrial experiments as well as on cosmic scales. For the oncoming neutrino, we use the Lorentz-covariant tachyonic relation ${E}_{\nu }=\sqrt{{\vec{p}}^{2}-{m}_{\nu }^{2}}$, where m ( )ν( ) is the tachyonic mass parameter. We derive both threshold conditions as well as on decay and energy loss rates, using the plane-wave fundamental bispinor solutions of the tachyonic Dirac equation. Various intricacies of rest frame versus lab frame calculations are highlighted. The results are compared to the observations of high-energy IceCube neutrinos of cosmological origin.

  • Cobimaximal lepton mixing from soft symmetry breaking
    Phys.Lett. B774 (2017) 325-331

    by: Grimus, W. (Vienna U.) et al.

    Cobimaximal lepton mixing, i.e. $\theta_{23} = 45^\circ$ and $\delta = \pm 90^\circ$ in the lepton mixing matrix $V$, arises as a consequence of $S V = V^\ast \mathcal{P}$, where $S$ is the permutation matrix that interchanges the second and third rows of $V$ and $\mathcal{P}$ is a diagonal matrix of phase factors. We prove that any such $V$ may be written in the form $V = U R P$, where $U$ is any predefined unitary matrix satisfying $S U = U^\ast$, $R$ is an orthogonal, i.e. real, matrix, and $P$ is a diagonal matrix satisfying $P^2 = \mathcal{P}$. Using this theorem, we demonstrate the equivalence of two ways of constructing models for cobimaximal mixing---one way that uses a standard $CP$ symmetry and a different way that uses a $CP$ symmetry including $\mu$--$\tau$ interchange. We also present two simple seesaw models to illustrate this equivalence; those models have, in addition to the $CP$ symmetry, flavour symmetries broken softly by the Majorana mass terms of the right-handed neutrino singlets. Since each of the two models needs four scalar doublets, we investigate how to accommodate the Standard Model Higgs particle in them.

  • Impact of Beyond the Standard Model Physics in the Detection of the Cosmic Neutrino Background
    JHEP 1709 (2017) 124

    by: Arteaga, Martín (Sao Paulo U.) et al.

    We discuss the effect of Beyond the Standard Model charged current interactions on the detection of the Cosmic Neutrino Background by neutrino capture on tritium in a PTOLEMY-like detector. We show that the total capture rate can be substantially modified for Dirac neutrinos if scalar or tensor right-chiral currents, with strength consistent with current experimental bounds, are at play. We find that the total capture rate for Dirac neutrinos, $\Gamma_{\rm D}^{\rm BSM}$, can be between 0.3 to 2.2 of what is expected for Dirac neutrinos in the Standard Model, $\Gamma_{\rm D}^{\rm SM}$, so that it can be made as large as the rate expected for Majorana neutrinos with only Standard Model interactions. A non-negligible primordial abundance of right-handed neutrinos can only worsen the situation, increasing $\Gamma_{\rm D}^{\rm BSM}$ by 30 to 90\%. On the other hand, if a much lower total rate is measured than what is expected for $\Gamma_{\rm D}^{\rm SM}$, it may be a sign of new physics.

  • High-Energy Neutrino Emission from Short Gamma-Ray Bursts: Prospects for Coincident Detection with Gravitational Waves
    Astrophys.J. 848 (2017) L4

    by: Kimura, Shigeo S. (Penn State U.) et al.

    We investigate current and future prospects for coincident detection of high-energy neutrinos and gravitational waves (GWs). Short gamma-ray bursts (SGRBs) are believed to originate from mergers of compact star binaries involving neutron stars. We estimate high-energy neutrino fluences from prompt emission, extended emission (EE), X-ray flares, and plateau emission, and we show that neutrino signals associated with the EE are the most promising. Assuming that the cosmic-ray loading factor is ∼10 and the Lorentz factor distribution is lognormal, we calculate the probability of neutrino detection from EE by current and future neutrino detectors, and we find that the quasi-simultaneous detection of high-energy neutrinos, gamma-rays, and GWs is possible with future instruments or even with current instruments for nearby SGRBs having EE. We also discuss stacking analyses that will also be useful with future experiments such as IceCube-Gen2.

  • A testable radiative neutrino mass model with multi-charged particles
    Phys.Lett. B774 (2017) 446-450

    by: Cheung, Kingman (Konkuk U.) et al.

    We propose a radiatively-induced neutrino mass model at one-loop level by introducing a pair of doubly-charged fermions and a few multi-charged bosons. We investigate the contributions of the model to neutrino masses, lepton-flavor violations, muon $g-2$, oblique parameters, and collider signals, and find a substantial fraction of the parameter space that can satisfy all the constraints. Furthermore, we discuss the possibility of detecting the doubly-charged fermions at the LHC.

  • Probing Direct and Indirect Unitarity Violation in Future Accelerator Neutrino Facilities
    Phys.Lett. B774 (2017) 217-224

    by: Tang, Jian (Zhongshan U.) et al.

    The possible existence of light and heavy sterile neutrinos may give rise to direct and indirect unitarity violation of the $3\times3$ lepton mixing matrix respectively. In the current work we study the potential of future accelerator neutrino facilities in probing the unitarity violation effects. Taking DUNE, T2HK and a low-energy Neutrino Factory (LENF) as working examples of future accelerator neutrino facilities, we study the distinct effects of direct and indirect unitarity violation on the discovery reach of the leptonic CP violation and precision measurements of $\theta_{23}$ in the three neutrino framework. In addition, constraints on the additional mixing parameters of direct and indirect unitarity violation are also discussed. Finally, we stress that the combination of experiments with different oscillation channels, different neutrino beams and different detector techniques will be an effective solution to the parameter degeneracy problem and give the robust measurement of leptonic CP violation even if the direct and indirect unitarity violation are taken into account.

  • Cornering the revamped BMV model with neutrino oscillation data
    Phys.Lett. B774 (2017) 179-182

    by: Chatterjee, Sabya Sachi (Bhubaneswar, Inst. Phys.) et al.

    Using the latest global determination of neutrino oscillation parameters from~\cite{deSalas:2017kay} we examine the status of the simplest revamped version of the BMV (Babu-Ma-Valle) model, proposed in~\cite{Morisi:2013qna}. The model predicts a striking correlation between the "poorly determined" atmospheric angle $\theta_{23}$ and CP phase $\delta_{CP}$, leading to either maximal CP violation or none, depending on the preferred $\theta_{23}$ octants. We determine the allowed BMV parameter regions and compare with the general three-neutrino oscillation scenario. We show that in the BMV model the higher octant is possible only at $99\%$ C.L., a stronger rejection than found in the general case. By performing quantitative simulations of forthcoming DUNE and T2HK experiments, using only the four "well-measured" oscillation parameters and the indication for normal mass ordering, we also map out the potential of these experiments to corner the model. The resulting global sensitivities are given in a robust form, that holds irrespective of the true values of the oscillation parameters.

  • Cobimaximal Neutrino Mixing from $A_4$ and its Possible Deviation
    Europhys.Lett. 119 (2017) 31001

    by: Ma, Ernest (UC, Riverside) et al.

    It has recently been shown that the phenomenologically successful pattern of cobimaximal neutrino mixing ($\theta_{13} \neq 0$, $\theta_{23} = \pi/4$, and $\delta_{CP} = \pm \pi/2$) may be achieved in the context of the non-Abelian discrete symmetry $A_4$, if the neutrino mass matrix is diagonalized by an orthogonal matrix ${\cal O}$. We study how this pattern would deviate if ${\cal O}$ is replaced by an unitary matrix.

  • Majorana Neutrino as Bogoliubov Quasiparticle
    Phys.Lett. B774 (2017) 273-278

    by: Fujikawa, Kazuo (Helsinki U.) et al.

    We suggest that the Majorana neutrino should be regarded as a Bogoliubov quasiparticle that is consistently understood only by use of a relativistic analogue of the Bogoliubov transformation. The unitary charge conjugation condition ${\cal C}\psi{\cal C}^{\dagger}=\psi$ is not maintained in the definition of a quantum Majorana fermion from a Weyl fermion. This is remedied by the Bogoliubov transformation accompanying a redefinition of the charge conjugation properties of vacuum, such that a C-noninvariant fermion number violating term (condensate) is converted to a Dirac mass. We also comment on the chiral symmetry of a Majorana fermion; a massless Majorana fermion is invariant under a global chiral transformation $\psi\rightarrow \exp[i\alpha\gamma_{5}]\psi$ and different Majorana fermions are distinguished by different chiral $U(1)$ charge assignments. The reversed process, namely, the definition of a Weyl fermion from a well-defined massless Majorana fermion is also briefly discussed.

  • Discovering intermediate mass sterile neutrinos through $\tau^- \to \pi^- \mu^- e^+ \nu$ (or $\bar{\nu}$) decay
    Phys.Rev. D96 (2017) 075016

    by: Kim, C.S. (Yonsei U.) et al.

    Distinguishing the Dirac and Majorana nature of neutrinos remains one of the most important tasks in neutrino physics. By assuming that the τ-→π-μ-e+ν(or ν¯) decay is resonantly enhanced by the exchange of an intermediate mass sterile neutrino N, we show that the energy spectrum of emitted pions and muons can be used to easily distinguish between the Dirac and Majorana nature of N. This method takes advantage of the fact that the flavor of light neutrinos is not identified in the tau decay under consideration. We find that it is particularly advantageous, because of no competing background events, to search for N in the mass range me+mμ≤mN≤mμ+mπ, where mX denotes the mass of particle X∈{e,μ,π,N}.

  • Sneutrino DM in the NMSSM with inverse seesaw mechanism
    JHEP 1710 (2017) 044

    by: Cao, Junjie (Henan Normal U.) et al.

    In supersymmetric theories like the Next-to-Minimal Supersymmetric Standard Model (NMSSM), the lightest neutralino with bino or singlino as its dominant component is customarily taken as dark matter (DM) candidate. Since light Higgsinos favored by naturalness can strength the couplings of the DM and thus enhance the DM-nucleon scattering rate, the tension between naturalness and DM direct detection results becomes more and more acute with the improved experimental sensitivity. In this work, we extend the NMSSM by inverse seesaw mechanism to generate neutrino mass, and show that in certain parameter space the lightest sneutrino may act as a viable DM candidate, i.e. it can annihilate by multi-channels to get correct relic density and meanwhile satisfy all experimental constraints. The most striking feature of the extension is that the DM-nucleon scattering rate can be naturally below its current experimental bounds regardless of the higgsino mass, and hence it alleviates the tension between naturalness and DM experiments. Other interesting features include that the Higgs phenomenology becomes much richer than that of the original NMSSM due to the relaxed constraints from DM physics and also due to the presence of extra neutrinos, and that the signatures of sparticles at colliders are quite different from those with neutralino as DM candidate.

  • Identifying the nature of dark matter at $e^{-}e^{+}$ colliders
    Phys.Rev. D96 (2017) 055029

    by: Baouche, Nabil (Algiers U.) et al.

    In this work, we consider the process $e^{+}+e^{-}\rightarrow b\bar{b}+\slashed{E}_{T}$, at the future electron-positron colliders such as the International Linear Collider and Compact Linear Collider, to look for the dark matter (DM) effect and identify its nature at two different center-of-mass energies $E_{c.m.}=500~\mathrm{GeV}~and~1~\mathrm{TeV}$. For this purpose, we take two extensions of the standard model, in which the DM could be a real scalar or a heavy right-handed neutrino (RHN) similar to many models motivated by neutrino mass. In the latter extension, the charged leptons are coupled to the RHNs via a lepton flavor violating interaction that involves a charged singlet scalar. After discussing different constraints, we define a set of kinematical cuts that suppress the background, and generate different distributions that are useful in identifying the DM nature. The use of polarized beams (like the polarization $P(e^{-},e^{+})=\left[+0.8,-0.3\right]$ at the International Linear Collider) makes the signal detection easier and the DM identification more clear, where the statistical significance gets enhanced by twice (five times) for scalar (RHN) DM.

  • A supersymmetric electroweak scale seesaw model
    JHEP 1710 (2017) 039

    by: Chang, Jung (Chonnam Natl. U.) et al.

    In this paper we propose a novel supersymmetric inverse seesaw model which has only one additional Z$_{6}$ symmetry. The field content is minimal to get a viable neutrino spectrum at tree-level. Interestingly, the inverse seesaw scale in our model is related to the scale of electroweak symmetry breaking. Due to that origin we are less biased about hierarchies and discuss three different types of the inverse seesaw mechanism with different phenomenologies. We can successfully reproduce neutrino masses and mixing and our model is consistent with current bounds on neutrinoless double beta decay, non-unitarity of the PMNS matrix and charged lepton flavor violation.

  • Leptogenesis and composite heavy neutrinos with gauge mediated interactions
    Eur.Phys.J. C77 (2017) 644

    by: Biondini, Simone (U. Bern, AEC) et al.

    Leptogenesis is an appealing framework to account for the baryon asymmetry in the universe. To this end physics beyond the standard model is demanded. In this paper we investigate the possibility to attain successful leptogenesis with composite Majorana neutrinos. We work in the framework of effective gauge-mediated and contact interactions without any reference to an underlying compositeness theory. This approach is the one adopted in all current experimental searches for composite fermions at colliders. In the case of gauge-mediated interactions, we calculate the CP asymmetry in heavy composite neutrino decays. Both the direct and the indirect CP asymmetry are derived and resonant leptogenesis is also discussed. We find that the Sakharov conditions can be met and, for some choice of the parameters, the correct order of magnitude of the baryon asymmetry is reproduced.

  • Lepton-Jets and Low-Mass Sterile Neutrinos at Hadron Colliders
    Phys.Rev. D96 (2017) 055031

    by: Dube, Sourabh (IISER, Pune) et al.

    Sterile neutrinos, if they exist, are potential harbingers for physics beyond the Standard Model. They have the capacity to shed light on our flavor sector, grand unification frameworks, dark matter sector and origins of baryon antibaryon asymmetry. There have been a few seminal studies that have broached the subject of sterile neutrinos with low, electroweak-scale masses (i.e. ΛQCD≪mNR≪mW±) and investigated their reach at hadron colliders using lepton jets. These preliminary studies nevertheless assume background-free scenarios after certain selection criteria which are overly optimistic and untenable in realistic situations. These lead to incorrect projections. The unique signal topology and challenging hadronic environment also make this mass-scale regime ripe for a careful investigation. With the above motivations, we attempt to perform the first systematic study of low, electroweak-scale, right-handed neutrinos at hadron colliders, in this unique signal topology. There are currently no active searches at hadron colliders for sterile neutrino states in this mass range, and we frame the study in the context of the 13 TeV high-luminosity Large Hadron Collider and the proposed FCC-hh/SppC 100 TeV pp-collider.

  • Minimal unified resolution to $R_{K^{(*)}}$ and $R(D^{(*)})$ anomalies with lepton mixing
    Phys.Rev.Lett. 119 (2017) 151801

    by: Choudhury, Debajyoti (Delhi U.) et al.

    It is a challenging task to explain, in terms of a simple and compelling new physics scenario, the intriguing discrepancies between the standard model expectations and the data for the neutral-current observables RK and RK*, as well as the charged-current observables R(D) and R(D*). We show that this can be achieved in an effective theory with only two unknown parameters. In addition, this class of models predicts some interesting signatures in the context of both B decays as well as high-energy collisions.

  • Spontaneous mirror left-right symmetry breaking for leptogenesis parametrized by Majorana neutrino mass matrix
    JHEP 1710 (2017) 016

    by: Gu, Pei-Hong (Shanghai Jiaotong U.)

    We introduce a mirror copy of the ordinary fermions and Higgs scalars for embedding the $SU(2)_L\times U(1)_Y$ electroweak gauge symmetry into an $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ left-right gauge symmetry. We then show the spontaneous left-right symmetry breaking can automatically break the parity symmetry motivated by solving the strong CP problem. Through the $SU(2)_R$ gauge interactions, a mirror Majorana neutrino can decay into a mirror charged lepton and two mirror quarks. Consequently we can obtain a lepton asymmetry stored in the mirror charged leptons. The Yukawa couplings of the mirror and ordinary charged fermions to a dark matter scalar then can transfer the mirror lepton asymmetry to an ordinary lepton asymmetry which provides a solution to the cosmic baryon asymmetry in association with the $SU(2)_L$ sphaleron processes. In this scenario, the baryon asymmetry can be well described by the neutrino mass matrix up to an overall factor.

  • Effect of collisions on neutrino flavor inhomogeneity in a dense neutrino gas
    Phys.Lett. B774 (2017) 258-267

    by: Cirigliano, Vincenzo (Los Alamos Natl. Lab., Theor. Div.) et al.

    We investigate the stability, with respect to spatial inhomogeneity, of a two-dimensional dense neutrino gas. The system exhibits growth of seed inhomogeneity due to nonlinear coherent neutrino self-interactions. In the absence of incoherent collisional effects, we observe a dependence of this instability growth rate on the neutrino mass spectrum: the normal neutrino mass hierarchy exhibits spatial instability over a larger range of neutrino number density compared to that of the inverted case. We further consider the effect of elastic incoherent collisions of the neutrinos with a static background of heavy, nucleon-like scatterers. At small scales, the growth of flavor instability can be suppressed by collisions. At large length scales we find, perhaps surprisingly, that for inverted neutrino mass hierarchy incoherent collisions fail to suppress flavor instabilities, independent of the coupling strength.

  • Sterile neutrino searches via displaced vertices at LHCb
    Phys.Lett. B774 (2017) 114-118

    by: Antusch, Stefan (Basel U.) et al.

    We explore the sensitivity of displaced vertex searches at LHCb for testing sterile neutrino extensions of the Standard Model towards explaining the observed neutrino masses. We derive estimates for the constraints on sterile neutrino parameters from a recently published displaced vertex search at LHCb based on run 1 data. They yield the currently most stringent limit on active-sterile neutrino mixing in the sterile neutrino mass range between 4.5 GeV and 10 GeV. Furthermore, we present forecasts for the sensitivities that could be obtained from the run 2 data and also for the high-luminosity phase of the LHC.

  • Dark Matter and Neutrino Mass from the Smallest Non-Abelian Chiral Dark Sector
    Phys.Rev. D96 (2017) 075010

    by: Berryman, Jeffrey M. (Northwestern U.) et al.

    All pieces of concrete evidence for phenomena outside the standard model (SM)—neutrino masses and dark matter—are consistent with the existence of new degrees of freedom that interact very weakly, if at all, with those in the SM. We propose that these new degrees of freedom organize themselves into a simple dark sector, a chiral SU(3)×SU(2) gauge theory with the smallest nontrivial fermion content. Similar to the SM, the dark SU(2) is spontaneously broken while the dark SU(3) confines at low energies. At the renormalizable level, the dark sector contains massless fermions—dark leptons—and stable massive particles—dark protons. We find that dark protons with masses between 10 and 100 TeV satisfy all current cosmological and astrophysical observations concerning dark matter even if dark protons are a symmetric thermal relic. The dark leptons play the role of right-handed neutrinos and allow simple realizations of the seesaw mechanism or the possibility that neutrinos are Dirac fermions. In the latter case, neutrino masses are also parametrically different from charged-fermion masses and the lightest neutrino is predicted to be massless. Since the new “neutrino” and “dark-matter” degrees of freedom interact with one another, these two new-physics phenomena are intertwined. Dark leptons play a nontrivial role in early Universe cosmology while indirect searches for dark matter involve, decisively, dark-matter annihilations into dark leptons. These, in turn, may lead to observable signatures at high-energy neutrino and gamma-ray observatories, especially once one accounts for the potential Sommerfeld enhancement of the annihilation cross section, derived from the low-energy dark-sector effective theory, a possibility we explore quantitatively in some detail.

  • A model of spontaneous $CP$ breaking at low scale
    Phys.Lett. B773 (2017) 252-257

    by: Abbas, Gauhar (Ahmedabad, Phys. Res. Lab)

    We introduce a CP symmetric model where masses of fermions are given by dimensional-5 operators, and CP is spontaneously broken at TeV scale. The unique feature of the model is that new CP symmetric gauge sector coexists with new CP symmetric fermions simultaneously at TeV scale. An ultraviolet completion of the model is also proposed. It is observed that the fine-tuning of the SM Higgs boson mass in this model is softened in a relatively small amount approximately up to 6 TeV . Other interesting consequences are presence of a possible dark matter candidate whose mass may be bounded from above by the SM Higgs mass. The model may also provide an explanation of recently observed flavour anomalies.

  • Heavy neutrinos from gluon fusion
    Phys.Rev. D96 (2017) 055042

    by: Ruiz, Richard (Durham U., IPPP) et al.

    Heavy neutrinos, a key prediction of many standard model extensions, remain some of the most searched-for objects at collider experiments. In this context, we revisit the premise that the gluon fusion production mechanism, $gg \to Z^*/h^* \to N\nu_\ell$, is phenomenologically irrelevant at the CERN LHC and report the impact of soft gluon corrections to the production cross section. We resum threshold logarithms up to next-to-next-to-next-to-leading logarithmic accuracy (N$^3$LL), thus capturing the dominant contributions to the inclusive cross section up to next-to-next-to-leading order (N$^2$LO). For $m_N > 150$ GeV and collider energies $\sqrt{s} = 7 - 100$ TeV, corrections to the Born rates span $+160$ to $+260\%$. At $\sqrt{s}$=14 TeV, the resummed channel is roughly equal in size to the widely-believed-to-be-dominant charged current Drell-Yan process and overtakes it outright at $\sqrt{s} \gtrsim 20-25$ TeV. Results are independent of the precise nature/mixing of $N$ and hold generically for other low-scale seesaws. Findings are also expected to hold for other exotic leptons and broken axial-vector currents, particularly as the $Z^*$ contribution identically reduces to that of a pseudoscalar.

  • Generalized Bottom-Tau unification, neutrino oscillations and dark matter: predictions from a lepton quarticity flavor approach
    Phys.Lett. B773 (2017) 26-33

    by: Centelles Chuliá, Salvador (Valencia U., IFIC) et al.

    We propose an A4 extension of the Standard Model with a Lepton Quarticity symmetry correlating dark matter stability with the Dirac nature of neutrinos. The flavor symmetry predicts (i) a generalized bottom-tau mass relation involving all families, (ii) small neutrino masses are induced a la seesaw , (iii) CP must be significantly violated in neutrino oscillations, (iv) the atmospheric angle θ23 lies in the second octant, and (v) only the normal neutrino mass ordering is realized.

  • Constraining sleptons at the LHC in a supersymmetric low-scale seesaw scenario
    Eur.Phys.J. C77 (2017) 661

    by: Cerna-Velazco, Nhell (Lima, Pont. U. Catolica) et al.

    We consider a scenario inspired by natural supersymmetry, where neutrino data is explained within a low-scale seesaw scenario. We extend the Minimal Supersymmetric Standard Model by adding light right-handed neutrinos and their superpartners, the R-sneutrinos, and consider the lightest neutralinos to be higgsino-like. We consider the possibilities of having either an R-sneutrino or a higgsino as lightest supersymmetric particle. Assuming that squarks and gauginos are heavy, we systematically evaluate the bounds on slepton masses due to existing LHC data.

  • Cosmic matter from dark electroweak phase transition with neutrino mass generation
    Phys.Rev. D96 (2017) 055038

    by: Gu, Pei-Hong (Shanghai Jiaotong U.)

    We consider a dark electroweak phase transition, during which a baryon asymmetry in the dark neutrons and an equal lepton asymmetry in the dark Dirac neutrinos can be simultaneously induced by the CP-violating reflection of the dark fermions off the expanding dark Higgs bubbles. The Yukawa couplings for generating the ordinary Majorana neutrino masses can partially convert the dark lepton asymmetry to an ordinary baryon asymmetry in association with the ordinary sphaleron processes. The dark neutron can have a determined mass to serve as a dark matter particle. By further imposing a proper mirror symmetry, the Majorana neutrino mass matrix can have the form of a linear seesaw, while its Dirac CP phase can provide a unique source for the required CP violation.

  • Neutrino CP phases from Sneutrino Chaotic Inflation
    Phys.Lett. B773 (2017) 179-185

    by: Nakayama, Kazunori (Tokyo U.) et al.

    We study if the minimal sneutrino chaotic inflation is consistent with a flavor symmetry of the Froggatt–Nielsen type, to derive testable predictions on the Dirac and Majorana CP violating phases, δ and α . For successful inflation, the two right-handed neutrinos, i.e., the inflaton and stabilizer fields, must be degenerate in mass. First we find that the lepton flavor symmetry structure becomes less manifest in the light neutrino masses in the seesaw mechanism, and this tendency becomes most prominent when right-handed neutrinos are degenerate. Secondly, the Dirac CP phase turns out to be sensitive to whether the shift symmetry breaking depends on the lepton flavor symmetry. When the flavor symmetry is imposed only on the stabilizer Yukawa couplings, distributions of the CP phases are peaked at δ≃±π/4,±3π/4 and α=0 , while the vanishing and maximal Dirac CP phases are disfavored. On the other hand, when the flavor symmetry is imposed on both the inflaton and stabilizer Yukawa couplings, it is rather difficult to explain the observed neutrino data, and those parameters consistent with the observation prefer the vanishing CP phases δ=0,π and α=0 .

  • Attenuation effect and neutrino oscillation tomography
    Phys.Rev. D96 (2017) 083009

    by: Ioannisian, A.N. (Yerevan State U.) et al.

    The attenuation effect is the effect of weakening contributions to the oscillation signal from remote structures of the matter density profile. The effect is a consequence of integration over the neutrino energy within the energy resolution interval. Structures of a density profile situated at distances larger than the attenuation length, λatt, are not “seen” at the level ε≡2EV/Δm2, where V is the matter potential. We show that the origins of attenuation are (i) the averaging of oscillations in certain layer(s) of matter, (ii) the smallness of the matter effect: ε≪1, and (iii) the specific initial and final states on neutrinos. We elaborate on the graphic description of the attenuation that allows us to compute explicitly the effects in the ε2 order for various density profiles and oscillation channels. The attenuation in the case of partial averaging is described. The effect is crucial for the interpretation of oscillation data and for the oscillation tomography of the Earth with low energy (solar, supernova, atmospheric, etc.) neutrinos.

  • Trimaximal $\mu$-$\tau$ reflection symmetry
    Phys.Rev. D96 (2017) 055039

    by: Rodejohann, Werner (Heidelberg, Max Planck Inst.) et al.

    The μ-τ reflection symmetry (νe,νμ,ντ)→(ν¯e,ν¯τ,ν¯μ) and the TM1 mixing (a Pontecorvo–Maki–Nakagawa–Sakata matrix with the first column fixed to the tribimaximal form) are both well compatible with experiments. If both approaches are simultaneously assumed, all lepton mixing parameters except for θ13 are predicted. In particular, one expects maximal CP violation (|δ|=90°), maximal atmospheric mixing (θ23=45°), a slightly less-than-tribimaximal solar mixing angle (θ12≈34°), as well as values of 0 or π for the two Majorana phases. We study the renormalization stability of this highly predictive framework when neutrino mass is described by an effective Weinberg operator and by the type I seesaw mechanism, both in the standard model and with supersymmetry.

  • Global Bayesian analysis of neutrino mass data
    Phys.Rev. D96 (2017) 073001

    by: Caldwell, Allen (Munich, Max Planck Inst.) et al.

    We perform a global Bayesian analysis of currently available neutrino data, putting data from oscillation experiments, neutrinoless double beta decay (0νββ), and precision cosmology on an equal footing. We evaluate the discovery potential of future 0νββ experiments and the Bayes factor of the two possible neutrino mass ordering schemes for different prior choices. We show that the indication for normal ordering is still very mild and does not strongly depend on realistic prior assumptions or different combinations of cosmological data sets. We find a wide range for 0νββ discovery potential, depending on the absolute neutrino mass scale, mass ordering and achievable background level.

  • A full analytic solution of $SO(10)$-inspired leptogenesis
    JHEP 1710 (2017) 029

    by: Di Bari, Pasquale (Southampton U.) et al.

    Recent encouraging experimental results on neutrino mixing parameters prompt further investigation on $SO(10)$-inspired leptogenesis and on the associated strong thermal solution that has correctly predicted a non-vanishing reactor mixing angle, it further predicts $\sin\delta \lesssim 0$, now supported by recent results at $\sim 95\%$ C.L., normally ordered neutrino masses and atmospheric mixing angle in the first octant, best fit results in latest global analyses. Extending a recent analytical procedure, we account for the mismatch between the Yukawa basis and the weak basis, that in $SO(10)$-inspired models is described by a CKM-like unitary transformation $V_L$, obtaining a full analytical solution that provides useful insight and reproduces accurately all numerical results, paving the way for future inclusion of different sources of theoretical uncertainties and for a statistical analysis of the constraints. We show how muon-dominated solutions appear for large values of the lightest neutrino mass in the range $(0.01$--$1)\,{\rm eV}$ but also how they necessarily require a mild fine tuning in the seesaw relation. For the dominant (and untuned) tauon-dominated solutions we show how, turning on $V_L \simeq V_{CKM}$, some of the constraints on the low energy neutrino parameters get significantly relaxed. In particular we show how the upper bound on the atmospheric neutrino mixing angle in the strong thermal solution gets relaxed from $\theta_{23} \lesssim 41^{\circ}$ to $\theta_{23} \lesssim 44^{\circ}$, an important effect in the light of the most recent NO$\nu$A, T2K and IceCube results.

  • Non-standard interactions of solar neutrinos in dark matter experiments
    Phys.Lett. B773 (2017) 242-246

    by: Dutta, Bhaskar (Texas A-M) et al.

    Non-standard neutrino interactions (NSI) affect both their propagation through matter and their detection, with bounds on NSI parameters coming from various astrophysical and terrestrial neutrino experiments. In this paper, we show that NSI can be probed in future direct dark matter detection experiments through both elastic neutrino-electron scattering and coherent neutrino-nucleus scattering, and that these channels provide complementary probes of NSI. We show NSI can increase the event rate due to solar neutrinos, with a sharp increase for lower nuclear recoil energy thresholds that are within reach for upcoming detectors. We also identify an interference range of NSI parameters for which the rate is reduced by approximately 40\%. Finally, we show that the "dark side" solution for the solar neutrino mixing angle may be discovered at forthcoming direct detection experiments.

  • Imprints of a light Sterile Neutrino at DUNE, T2HK and T2HKK
    Phys.Rev. D96 (2017) 056026

    by: Choubey, Sandhya (Royal Inst. Tech., Stockholm) et al.

    We evaluate the impact of sterile neutrino oscillations in the so-called 3+1 scenario on the proposed long baseline experiment in USA and Japan. There are two proposals for the Japan experiment which are called T2HK and T2HKK. We show the impact of sterile neutrino oscillation parameters on the expected sensitivity of T2HK and T2HKK to mass hierarchy, CP violation and octant of θ23 and compare it against that expected in the case of standard oscillations. We add the expected ten years data from DUNE and present the combined expected sensitivity of T2HKK+DUNE to the oscillation parameters. We do a full marginalization over the relevant parameter space and show the effect of the magnitude of the true sterile mixing angles on the physics reach of these experiments. We show that if one assumes that the source of CP violation is the standard CP phase alone in the test case, then it appears that the expected CP violation sensitivity decreases due to sterile neutrinos. However, if we give up this assumption, then the CP sensitivity could go in either direction. The impact on expected octant of θ23 and mass hierarchy sensitivity is shown to depend on the magnitude of the sterile mixing angles in a nontrivial way.

  • Reconsidering the One Leptoquark solution: flavor anomalies and neutrino mass
    JHEP 1710 (2017) 047

    by: Cai, Yi (ARC, CoEPP, Melbourne) et al.

    We reconsider a model introducing a scalar leptoquark $\phi \sim (\mathbf{3}, \mathbf{1}, -1/3)$ to explain recent deviations from the standard model in semileptonic $B$ decays. The leptoquark can accommodate the persistent tension in the decays $\bar{B}\rightarrow D^{(*)}\tau \bar{\nu}$ as long as its mass is lower than approximately $10 \text{ TeV}$, and we show that a sizeable Yukawa coupling to the right-chiral tau lepton is necessary for an acceptable explanation. Agreement with the measured $\bar{B}\rightarrow D^{(*)}\tau \bar{\nu}$ rates is mildly compromised for parameter choices addressing the tensions in $b \to s \mu \mu$, where the model can significantly reduce the discrepancies in angular observables, branching ratios and the lepton-flavor-universality observables $R_K$ and $R_{K^*}$. The leptoquark can also reconcile the predicted and measured value of the anomalous magnetic moment of the muon and appears naturally in models of radiative neutrino mass derived from lepton-number violating effective operators. As a representative example, we incorporate the particle into an existing two-loop neutrino mass scenario derived from a dimension-nine operator. In this specific model, the structure of the neutrino mass matrix provides enough freedom to explain the small masses of the neutrinos in the region of parameter space dictated by agreement with the anomalies in $\bar{B}\rightarrow D^{(*)}\tau \bar{\nu}$, but not the $b \to s$ transition. This is achieved without excessive fine-tuning in the parameters important for neutrino mass.

  • Study of parameter degeneracy and hierarchy sensitivity of NO$\nu$A in presence of sterile neutrino
    Phys.Rev. D96 (2017) 075018

    by: Ghosh, Monojit (Tokyo Metropolitan U.) et al.

    The first hint of the neutrino mass hierarchy is believed to come from the long-baseline experiment NOνA. Recent results from NOνA shows a mild preference towards the CP phase δ13=-90° and normal hierarchy. Fortunately this is the favorable area of the parameter space which does not suffer from the hierarchy-δ13 degeneracy and thus NOνA can have good hierarchy sensitivity for this true combination of hierarchy and δ13. Apart from the hierarchy-δ13 degeneracy there is also the octant-δ13 degeneracy. But this does not affect the favorable parameter space of NOνA as this degeneracy can be resolved with a balanced neutrino and antineutrino run. However, if we consider the existence of a light sterile neutrino then there may be additional degeneracies which can spoil the hierarchy sensitivity of NOνA even in the favorable parameter space. In the present work we find that apart from the degeneracies mentioned above, there are additional hierarchy and octant degeneracies that appear with the new phase δ14 in the presence of a light sterile neutrino in the eV scale. In contrast to the hierarchy and octant degeneracies appearing with δ13, the parameter space for hierarchy-δ14 degeneracy is different in neutrinos and antineutrinos though the octant-δ14 degeneracy behaves similarly in neutrinos and antineutrinos. We study the effect of these degeneracies on the hierarchy sensitivity of NOνA for the true normal hierarchy.

  • Effective Sextic Superpotential and $B-L$ violation in NMSGUT
    Pramana 89 (2017) 51

    by: Aulakh, Charanjit S. (IISER, Mohali) et al.

    We list operators of the superpotential of the effective MSSM that emerges from the NMSGUT up to sextic degree. We give illustrative expressions for the coefficients in terms of NMSGUT parameters. We also estimate the impact of GUT scale threshold corrections on these effective operators in view of the demonstration that $B$ violation via quartic superpotential terms can be suppressed to acceptable levels after including such corrections in the NMSGUT. We find a novel $B, B-L$ violating quintic operator that leads to the decay mode $n\to e^- K^+$. We also remark that the threshold corrections to the Type I seesaw mechanism make the deviation of right handed neutrino masses from the GUT scale more natural while Type II seesaw neutrino masses, which earlier tended to utterly negligible receive threshold enhancement. Our results are of relevance for analyzing $B-L$ violating operator based, sphaleron safe, Baryogenesis.

  • Changing the prior: absolute neutrino mass constraints in nonlocal gravity
    Phys.Rev. D96 (2017) 083513

    by: Dirian, Yves (Geneva U., CAP)

    Prior change is discussed in observational constraints studies of nonlocally modified gravity. In the latter, a model characterized by a modification of the form $\sim m^2 R\Box^{-2}R$ to the Einstein-Hilbert action was compared against the base $\Lambda$CDM one in a Bayesian way. It was found that the competing modified gravity model is significantly disfavored (at $22 \,$:$\, 1$ in terms of betting-odds) against $\Lambda$CDM given CMB+SNIa+BAO data, because of a dominant tension appearing in the $H_0 \,$-$\, \Omega_M$ plan. We identify the underlying mechanism generating such a tension and show that it is mostly caused by the late-time, quite smooth, phantom nature of the effective dark energy described by the nonlocal model. We find possible solutions for it to be resolved and explore a given one that consists in extending the initial baseline from one massive neutrino eigenstate to three degenerate ones, whose absolute mass $\sum m_\nu \, / \, 3$ is allowed to take values within a reasonable prior interval. As a net effect, the absolute neutrino mass is inferred to be non-vanishing at $2 \sigma$ level, best-fitting at $\sum m_\nu \approx 0.21 {\, \rm eV}$, and the Bayesian tension disappears rendering the nonlocal gravity model statistically equivalent to $\Lambda$CDM, given recent CMB+SNIa+BAO data. We also discuss constraints from growth rate measurements $f \sigma_8$ whose fit is found to be improved by a larger massive neutrino fraction as well. The $\nu$-extended nonlocal model also prefers a higher value of $H_0$ than $\Lambda$CDM, therefore in better agreement with local measurements.

  • Initial condition for baryogenesis via neutrino oscillation
    Phys.Rev. D96 (2017) 083010

    by: Asaka, Takehiko (Niigata U.) et al.

    We consider a baryogenesis scenario via the oscillation of right-handed neutrinos with Majorana masses of the order of GeV, which are also responsible for neutrino masses by the seesaw mechanism. We study how the initial condition alters the prediction of the present baryon asymmetry by this mechanism. It is usually assumed that the abundance of right-handed neutrinos is zero after the reheating of the inflationary universe and they are produced in scattering processes by the renomalizable Yukawa interaction. However, the higher dimensional operator with right-handed neutrinos may provide an additional production which is most effective at the reheating epoch. It is shown that such an initial abundance of right-handed neutrinos can significantly modify the prediction when the strong washout of the asymmetry is absent. This leads that the parameter space of the model for the successful baryogenesis is enlarged.

  • Generation of a radiative neutrino mass in the linear seesaw framework, charged lepton flavor violation, and dark matter
    Phys.Rev. D96 (2017) 075001

    by: Das, Arindam (Korea Inst. Advanced Study, Seoul) et al.

    We investigate a model with local U(1)B-L and discrete Z2 symmetries where two types of weak isospin singlet neutrinos, vectorlike charged leptons, and exotic scalar fields are introduced. The linear seesaw mechanism is induced at the one-loop level through Yukawa interactions associated with the standard model leptons and exotic fields. We also discuss lepton flavor violation and a muon anomalous dipole magnetic moment induced by the new Yukawa interaction. In addition, our model has dark matter candidate which is the lightest Z2 odd neutral particle. We calculate the relic density and constraints from direct detection.

  • Radiatively Generating the Higgs Potential and Electroweak Scale via the Seesaw Mechanism
    Phys.Rev.Lett. 119 (2017) 141801

    by: Brivio, Ilaria (Bohr Inst.) et al.

    The minimal seesaw scenario can radiatively generate the Higgs potential to induce electroweak symmetry breaking while supplying an origin of the Higgs vacuum expectation value from an underlying Majorana scale. If the Higgs potential and (derived) electroweak scale have this origin, the heavy SU(3)×SU(2)×U(1)Y singlet states are expected to reside at mN∼10–500  PeV for couplings |ω|∼10-4.5-10-6 between the Majorana sector and the standard model. In this framework, the usual challenge of the electroweak scale hierarchy problem with a classically assumed potential is absent as the electroweak scale is not a fundamental scale. The new challenge is the need to generate or accommodate PeV Majorana mass scales while simultaneously suppressing tree-level contributions to the potential in ultraviolet models.

  • Baryogenesis at a Lepton-Number-Breaking Phase Transition
    JHEP 1710 (2017) 095

    by: Long, Andrew J. (Chicago U., KICP) et al.

    We study a scenario in which the baryon asymmetry of the universe arises from a cosmological phase transition where lepton-number is spontaneously broken. If the phase transition is first order, a lepton-number asymmetry can arise at the bubble wall, through dynamics similar to electroweak baryogenesis, but involving right-handed neutrinos. In addition to the usual neutrinoless double beta decay in nuclear experiments, the model may be probed through a variety of "baryogenesis by-products," which include a stochastic background of gravitational waves created by the colliding bubbles. Depending on the model, other aspects may include a network of topological defects that produce their own gravitational waves, additional contribution to dark radiation, and a light pseudo-Goldstone boson (majoron) as dark matter candidate.

  • Strong CP problem, axions, and cosmological implications of CP violation
    PoS CORFU2016 (2017) 037

    by: Kim, Jihn E. (IBS, Daejeon)

    In this talk, I present a pedagogical and historical review related to the CP symmetry. It includes the weak CP violation, the strong CP problem, "invisible" axions and cosmology, and Type-II leptogenesis.

  • Long Lived Light Scalars as Probe of Low Scale Seesaw Models
    Nucl.Phys. B923 (2017) 179-221

    by: Dev, P. S. Bhupal (Washington U., St. Louis) et al.

    We point out that in generic TeV scale seesaw models for neutrino masses with local $B-L$ symmetry breaking, there is a phenomenologically allowed range of parameters where the Higgs field responsible for $B-L$ symmetry breaking leaves a physical real scalar field with mass around GeV scale. This particle (denoted here by $H_3$) is weakly mixed with the Standard Model Higgs field ($h$) with mixing $\theta_1\lesssim m_{H_3}/m_h$, barring fine-tuned cancellation. In the specific case when the $B-L$ symmetry is embedded into the TeV scale left-right seesaw scenario, we show that the bounds on the $h-H_3$ mixing $\theta_1$ become further strengthened due to low energy flavor constraints, thus forcing the light $H_3$ to be long lived, with displaced vertex signals at the LHC. The property of left-right TeV scale seesaw models are such that they make the $H_3$ decay to two photons as the dominant mode. This is in contrast with a generic light scalar that mixes with the SM Higgs boson, which could also have leptonic and hadronic decay modes with comparable or larger strength. We discuss the production of this new scalar field at the LHC and show that it leads to testable displaced vertex signals of collimated photon jets, which is a new distinguishing feature of the left-right seesaw model. We also study a simpler version of the model where the $SU(2)_R$ breaking scale is much higher than the ${\cal O}$(TeV) $U(1)_{B-L}$ breaking scale, in which case the production and decay of $H_3$ proceed differently, but its long lifetime feature is still preserved for a large range of parameters. Thus, the search for such long-lived light scalar particles provides a new way to probe TeV scale seesaw models for neutrino masses at colliders.

  • Probing light sterile neutrino signatures at reactor and Spallation Neutron Source neutrino experiments
    Phys.Rev. D96 (2017) 063013

    by: Kosmas, T.S. (Ioannina U.) et al.

    We investigate the impact of a fourth sterile neutrino at reactor and Spallation Neutron Source neutrino detectors. Specifically, we explore the discovery potential of the TEXONO and COHERENT experiments to subleading sterile neutrino effects through the measurement of the coherent elastic neutrino-nucleus scattering event rate. Our dedicated $\chi^2$-sensitivity analysis employs realistic nuclear structure calculations adequate for high purity sub-keV threshold Germanium detectors.

  • Bounds on heavy Majorana neutrinos in type-I seesaw and implications for collider searches
    Phys.Lett. B774 (2017) 32-40

    by: Das, Arindam (Korea Inst. Advanced Study, Seoul) et al.

    The neutrino masses and flavor mixings, which are missing in the Standard Model (SM), can be naturally incorporated in the type-I seesaw extension of the SM with heavy Majorana neutrinos being singlet under the SM gauge group. If the heavy Majorana neutrinos are around the electroweak scale and their mixings with the SM neutrinos are sizable, they can be produced at high energy colliders, leaving characteristic signatures with lepton-number violations. Employing the general parametrization for the neutrino Dirac mass matrix in the minimal seesaw scenario, we perform a parameter scan and identify allowed regions to satisfy a variety of experimental constraints from the neutrino oscillation data, the electroweak precision measurements and the lepton-flavor violating processes. We find that the resultant mixing parameters between the heavy neutrinos and the SM neutrinos are more severely constrained than those obtained from the current search for heavy Majorana neutrinos at the LHC. Such parameter regions can be explored at the High-Luminosity LHC and a 100 TeV pp-collider in the future.

  • Implications of residual CP symmetry for leptogenesis in a model with two right-handed neutrinos
    Phys.Rev. D96 (2017) 075005

    by: Li, Cai-Chang (Hefei, CUST) et al.

    We analyze the interplay between leptogenesis and residual symmetry in the framework of a model with two right-handed neutrinos. Working in the flavor basis, we show that all the leptogenesis CP asymmetries are vanishing for the case of two residual CP transformations or a cyclic residual flavor symmetry in the neutrino sector. If a single remnant CP transformation is preserved in the neutrino sector, the lepton mixing matrix is determined up to a real orthogonal matrix multiplied from the right side. The R-matrix is found to depend on only one real parameter. It can take three viable forms, and each entry is either real or purely imaginary. The baryon asymmetry is generated entirely by the CP violating phases in the mixing matrix in this scenario. We perform a comprehensive study for the Δ(6n2) flavor group and CP symmetry which are broken into a single remnant CP transformation in the neutrino sector and an Abelian subgroup in the charged lepton sector. The results for lepton flavor mixing and leptogenesis are presented.

  • Natural emergence of neutrino masses and dark matter from $R$-symmetry
    JHEP 1710 (2017) 012

    by: Chakraborty, Sabyasachi (TIFR, Mumbai, Dept. Theor. Phys.) et al.

    We propose a supersymmetric extension of the Standard Model (SM) with a continuous global $U(1)_R$ symmetry. The $R$-charges of the SM fields are identified with that of their lepton numbers. As a result, both bilinear and trilinear `$R$-parity violating' (RPV) terms could be present at the superpotential. However, $R$-symmetry is not an exact symmetry as it is broken by supergravity effects. Hence, sneutrinos acquire a small vacuum expectation value in this framework. However, a suitable choice of basis ensures that the bilinear RPV terms can be completely rotated away from the superpotential and the scalar potential. On the other hand, the trilinear terms play a very crucial role in generating neutrino masses and mixing at the tree level. This is noticeably different from the typical $R$-parity violating Minimal Supersymmetric Standard Model. Also, gravitino mass turns out to be the order parameter of $R$-breaking and is directly related to the neutrino mass. We show that such a gravitino, within the mass range $200~\text{keV}\lesssim m_{3/2}\lesssim 0.1~\text{GeV}$ can be an excellent dark matter candidate. Finally, we looked into the collider implications of our framework.

  • An optimization-based approach to calculating neutrino flavor evolution
    Phys.Rev. D96 (2017) 083008

    by: Armstrong, Eve (UC, San Diego) et al.

    We assess the utility of an optimization-based data assimilation (D.A.) technique for treating the problem of nonlinear neutrino flavor transformation in core-collapse supernovae. D.A. uses measurements obtained from a physical system to estimate the state variable evolution and parameter values of the associated model. Formulated as an optimization procedure, D.A. can offer an integration-blind approach to predicting model evolution, which offers an advantage for models that thwart solution via traditional numerical integration techniques. Further, D.A. performs most optimally for models whose equations of motion are nonlinearly coupled. In this exploratory work, we consider a simple steady-state model with two monoenergetic neutrino beams coherently interacting with each other and a background medium. As this model can be solved via numerical integration, we have an independent consistency check for D.A. solutions. We find that the procedure can capture key features of flavor evolution over the entire trajectory, even given measurements of neutrino flavor only at the endpoint, and with an assumed known initial flavor distribution. Further, the procedure permits an examination of the sensitivity of flavor evolution to estimates of unknown model parameters, locates degeneracies in parameter space, and can identify the specific measurements required to break those degeneracies.

  • Constraints and prospects on gravitational-wave and neutrino emissions using GW150914
    Phys.Rev. D96 (2017) 083003

    by: de Vries, Krijn D. (Brussels U., IIHE) et al.

    Recently, the LIGO observatory reported the first direct observation of gravitational waves, with a signal consistent with a binary black hole merger. This detection triggered several follow-up searches for coincident emission in electromagnetic waves as well as neutrinos, but no such emission was found. In this article, the implications of the nondetection of counterpart neutrinos are investigated using general arguments. The results are interpreted with a parameter denoting the energy emitted in neutrinos relative to the energy emitted in gravitational waves. The bound on this parameter from the diffuse astrophysical neutrino flux detected by the IceCube Neutrino Observatory is discussed. It is found that, currently, the nondetection of counterpart neutrinos puts a bound comparable to the one from the diffuse astrophysical neutrino flux. This bound is then used to constrain the amount of matter in the black hole binary environment. Finally, the sensitivity to this parameter in future gravitational wave observation runs is investigated. It is shown how the detection of one or more neutrinos from a single merger would strongly constrain the source population and evolution.

  • Can nonstandard interactions jeopardize the hierarchy sensitivity of DUNE ?
    Phys.Rev. D96 (2017) 075023

    by: Deepthi, K.N. (Ahmedabad, Phys. Res. Lab) et al.

    We study the effect of non-standard interactions (NSIs) on the propagation of neutrinos through the Earth matter and how it affects the hierarchy sensitivity of the DUNE experiment. We emphasize on the special case when the diagonal NSI parameter $\epsilon_{ee} = -1$, nullifying the standard matter effect. We show that, if in addition, CP violation is maximal then this gives rise to an exact intrinsic hierarchy degeneracy in the appearance channel, irrespective of the baseline and energy. Introduction of off-diagonal NSI parameter, $\epsilon_{e \tau}$, shifts the position of this degeneracy to a different $\epsilon_{ee}$. Moreover the unknown magnitude and phases of the off-diagonal NSI parameters can give rise to additional degeneracies. Overall, given the current model independent limits on NSI parameters, the hierarchy sensitivity of DUNE can get seriously impacted. However, a more precise knowledge on the NSI parameters, specially $\epsilon_{ee}$, can give rise to an improved sensitivity. Alternatively, if NSI exists in nature, and still DUNE shows hierarchy sensitivity, certain ranges of the NSI parameters can be excluded. Additionally, we briefly discussed the implications of $\epsilon_{ee} = -1$ (in the Earth) on MSW effect in the Sun.

  • One Leptoquark to unify them? Neutrino masses and unification in the light of $(g-2)_\mu$, $R_{D^{(\star)}}$ and $R_K$ anomalies
    Nucl.Phys. B923 (2017) 324-338

    by: Popov, Oleg (UC, Riverside) et al.

    Leptoquarks have been proposed as a possible explanation of anomalies in B¯↦D⁎τν¯ decays, the apparent anomalies in (g−2)μ experiments and a violation of lepton universality. Motivated by this, we examine other motivations of leptoquarks: radiatively induced neutrino masses in the presence of a discrete symmetry that prevents a tree level see-saw mechanism, gauge coupling unification, and vacuum stability at least up to the unification scale. We present a new model for radiatively generating a neutrino mass which can significantly improve gauge coupling unification at one loop. We discuss this, and other models in the light of recent work on flavour anomalies.

  • Mixed Inert Scalar Triplet Dark Matter, Radiative Neutrino Masses and Leptogenesis
    Nucl.Phys. B924 (2017) 279-311

    by: Lu, Wen-Bin (Shanghai Jiaotong U.) et al.

    The neutral component of an inert scalar multiplet with hypercharge can provide a stable dark matter particle when its real and imaginary parts have a splitting mass spectrum. Otherwise, a tree-level dark matter-nucleon scattering mediated by the $Z$ boson will be much above the experimental limit. In this paper we focus on a mixed inert scalar triplet dark matter scenario where a complex scalar triplet with hypercharge can mix with another real scalar triplet without hypercharge through their renormalizable coupling to the standard model Higgs doublet. We consider three specified cases that carry most of the relevant features of the full parameter space: (i) the neutral component of the real triplet dominates the dark matter particle, (ii) the neutral component of the complex triplet dominates the dark matter particle; and (iii) the neutral components of the real and complex triplets equally constitute the dark matter particle. Subject to the dark matter relic abundance and direct detection constraint, we perform a systematic study on the allowed parameter space with particular emphasis on the interplay among triplet-doublet terms and gauge interactions. In the presence of these mixed inert scalar triplets, some heavy Dirac fermions composed of inert fermion doublets can be utilized to generate a tiny Majorana neutrino mass term at one-loop level and realize a successful leptogenesis for explaining the cosmic baryon asymmetry.

  • Probing Majorana Neutrino Textures at DUNE
    Phys.Rev. D96 (2017) 075006

    by: Bora, Kalpana (Gauhati U.) et al.

    We study the possibility of probing different texture zero neutrino mass matrices at the long baseline neutrino experiment DUNE, particularly focusing on its sensitivity to the octant of atmospheric mixing angle θ23 and leptonic Dirac CP phase δcp. Assuming a diagonal charged lepton basis and Majorana nature of light neutrinos, we first classify the possible light neutrino mass matrices with one and two texture zeros and then numerically evaluate the parameter space which satisfies the texture zero conditions. Apart from using the latest global fit 3σ values of neutrino oscillation parameters, we also use the latest bound on the sum of absolute neutrino masses (∑i|mi|) from the Planck mission data and the updated bound on effective neutrino mass Mee from neutrinoless double beta decay (0νββ) experiments to find the allowed Majorana texture zero mass matrices. For the allowed texture zero mass matrices from all these constraints, we then feed the corresponding light neutrino parameter values satisfying the texture zero conditions into the numerical analysis in order to study the capability of DUNE to allow or exclude them once it starts taking data. We find that DUNE will be able to exclude some of these texture zero mass matrices which restrict (θ23-δcp) to a very specific range of values, depending on the values of the parameters that nature has chosen.

  • The Physics of antineutrinos in DUNE and resolution of octant degeneracy
    J.Phys.Conf.Ser. 888 (2017) 012261

    by: Nath, Newton (Ahmedabad, Phys. Res. Lab) et al.

    We study the capability of the DUNE experiment, which will be the first beam based experiment with a wide band flux profile, to uncover the octant of the leptonic mixing angle $\theta_{23}$ (i.e., $\theta_{23}$ is $< 45^\circ$ or $>45^\circ$). In this work, we find that for the DUNE baseline of 1300 km, due to enhanced matter effect, the neutrino and antineutrino probabilities are different which creates a tension in the case of combined runs because of which octant sensitivity also can come from disappearance channel. In view of this, we study the physics of antineutrinos in DUNE and explore the role of antineutrinos run that is required to resolve the octant degeneracy at a certain confidence levels.

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