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  • A new mechanism of sterile neutrino dark matter production

    by: Herms, Johannes
    We consider a scenario where the dark matter candidate is a sterile neutrino with sizable self-interactions, described by a dimension-six operator, and with negligible interactions with the Standard Model. The relic abundance is set by the freeze-out of 4-to-2 annihilations in the dark sector plasma and reproduces the observed dark matter abundance when the sterile neutrino mass is in the range $\sim 300\,{\rm keV} - 100\,\,{\rm GeV}$. The feeble interactions with the Standard Model may lead to observable signals from dark matter decay. Furthermore, the self-interactions can affect the formation of small scale structures. We also implement this mechanism in a concrete model where the sterile neutrino self-interaction is due to the exchange of a singlet scalar, and we discuss the relevance of the scalar portal interactions for constructing a complete thermal history of the dark sector.

  • Supernova Neutrino Neutrino Astronomy

    by: Brdar, Vedran (MPIK Heidelberg) et al.

    Modern neutrino facilities will be able to detect a large number of neutrinos from the next Galactic supernova. We investigate the viability of the triangulation method to locate a core-collapse supernova by employing the neutrino arrival time differences at various detectors. We perform detailed numerical fits in order to determine the uncertainties of these time differences for the cases when the core collapses into a neutron star or a black hole. We provide a global picture by combining all the relevant current and future neutrino detectors. Our findings indicate that in the scenario of a neutron star formation, supernova can be located with precision of 1.5 and 3.5 degrees in declination and right ascension, respectively. For the black hole scenario, sub-degree precision can be reached.

  • Dirac neutrino mixings from hidden $\mu-\tau$ symmetry

    by: Terrazas, Edgar R. Luna
    We explore masses and mixings for Dirac neutrinos in models where lepton number is conserved, under the guidance of a hidden, but broken, $\mu-\tau$ exchange symmetry, that makes itself evident in the squared hermitian mass matrix. We study the parameter space in the most general theory as allowed by current neutrino oscillation experiment data. By using a general parameterization of the mass matrix which contains only observable parameters we stablish that the amount of breaking of the symmetry is in the range of the atmospheric mass scale, without regard to the neutrino hierarchy, the absolute neutrino mass and the Dirac CP phase. An estimate of the invisible branching ratio for a Higgs boson decaying into Dirac neutrinos, $H\rightarrow\nu\overline{\nu}$ , is given and compared to recent measurements in this context.

  • Fully Constrained Majorana Neutrino Mass Matrices Using $\Sigma(72\times 3)$
    Eur.Phys.J. C78 (2018) 74

    by: Krishnan, R. (Warwick U.) et al.

    In 2002, two neutrino mixing ansatze having trimaximally-mixed middle ($\nu_2$) columns, namely tri-chi-maximal mixing ($\text{T}\chi\text{M}$) and tri-phi-maximal mixing ($\text{T}\phi\text{M}$), were proposed. In 2012, it was shown that $\text{T}\chi\text{M}$ with $\chi=\pm \frac{\pi}{16}$ as well as $\text{T}\phi\text{M}$ with $\phi = \pm \frac{\pi}{16}$ leads to the solution, $\sin^2 \theta_{13} = \frac{2}{3} \sin^2 \frac{\pi}{16}$, consistent with the latest measurements of the reactor mixing angle, $\theta_{13}$. To obtain $\text{T}\chi\text{M}_{(\chi=\pm \frac{\pi}{16})}$ and $\text{T}\phi\text{M}_{(\phi=\pm \frac{\pi}{16})}$, the type~I see-saw framework with fully constrained Majorana neutrino mass matrices was utilised. These mass matrices also resulted in the neutrino mass ratios, $m_1:m_2:m_3=\frac{\left(2+\sqrt{2}\right)}{1+\sqrt{2(2+\sqrt{2})}}:1:\frac{\left(2+\sqrt{2}\right)}{-1+\sqrt{2(2+\sqrt{2})}}$. In this paper we construct a flavour model based on the discrete group $\Sigma(72\times 3)$ and obtain the aforementioned results. A Majorana neutrino mass matrix (a symmetric $3\times 3$ matrix with 6 complex degrees of freedom) is conveniently mapped into a flavon field transforming as the complex 6 dimensional representation of $\Sigma(72\times 3)$. Specific vacuum alignments of the flavons are used to arrive at the desired mass matrices.

  • A Sterile Neutrino Origin for the Upward Directed Cosmic Ray Shower Detected by ANITA

    by: Cherry, John F.
    The ANITA balloon experiment has observed an EeV cascade event at an angle below the horizon that renders any Standard Model (SM) interpretation unlikely as the Earth is significantly opaque to all SM particles at such energies. In this paper, we study a sterile neutrino interpretation of this event, calculating the angular event distribution of cascades and the relative sensitivities of several experiments to a cascade initiated by an EeV sterile neutrino. We find that ANITA is uniquely sensitive to this type of upward directed cascade signal and canonical ultrahigh energy cosmic ray (UHECR) models can produce a reprocessed EeV sterile neutrino flux at sufficient levels to accommodate the ANITA event.

  • Exploring the Potential of Short-Baseline Physics at Fermilab

    by: Miranda, O.G.
    We study the capabilities of the short baseline neutrino program at Fermilab to probe the unitarity of the lepton mixing matrix. We find the sensitivity to be slightly better than the current one. Motivated by the future DUNE experiment, we have also analyzed the potential of an extra liquid Argon near detector in the LBNF beamline. Adding such a near detector to the DUNE setup will substantially improve the current sensitivity on non-unitarity. This would help to remove CP degeneracies due to the new complex phase present in the neutrino mixing matrix. We also comment on the sensitivity of this setup to light sterile neutrinos for various configurations.

  • Status of the semileptonic $B$ decays and muon g-2 in general 2HDMs with right-handed neutrinos

    by: Iguro, Syuhei
    In this paper, we study the extended Standard Model (SM) with an extra Higgs doublet and right-handed neutrinos. If the symmetry to distinguish the two Higgs doublets is not assigned, flavor changing neutral currents (FCNCs) involving the scalars are predicted even at the tree level. We investigate the constraints on the FCNCs at the one-loop level, and especially study the semileptonic $B$ meson decays, e.g. $B \to D^{(*)} \tau \nu$ and $B \to K^{(*)} ll$ processes, where the SM predictions are more than $2 \sigma$ away from the experimental results. We also consider the flavor-violating couplings involving right-handed neutrinos and discuss if the parameters to explain the excesses of the semileptonic $B$ decays can resolve the discrepancy in the the anomalous muon magnetic moment. Based on the analysis, we propose the smoking-gun signals of our model at the LHC.

  • Impact of medium modification of the nucleon weak and electromagnetic form factors on the neutrino mean free path in dense matter

    by: Hutauruk, Parada T.P.
    Impact of the in-medium modified nucleon weak and electromagnetic form factors on the neutrino mean free path in dense matter is studied by considering both the weak and electromagnetic interactions of neutrinos with the constituents of the matter. A relativistic mean field model and the quark-meson coupling model are respectively adopted for the in-medium effective nucleon mass and nucleon form factors. We find that the cross sections of neutrino scattering in cold nuclear medium decreases when the in-medium modification of the nucleon weak and electromagnetic form factors are taken into account. This reduction results in the enhancement of the neutrino mean free path, in particular, at the baryon density of around a few times the normal nuclear matter density. The enhancement of the neutrino mean free path is estimated to be about 10-40% compared with the values obtained without the medium modification of the nucleon form factors, which enhances the cooling of neutron stars.

  • Solar Neutrinos as a Signal and Background in Direct-Detection Experiments Searching for Sub-GeV Dark Matter With Electron Recoils

    by: Essig, Rouven
    Direct-detection experiments sensitive to low-energy electron recoils from sub-GeV dark matter (DM) interactions will also be sensitive to solar neutrinos via coherent neutrino-nucleus scattering (CNS), since the recoiling nucleus can produce a small ionization signal. Solar neutrinos constitute both an interesting signal in their own right and a potential background to a DM search that cannot be controlled or reduced by improved shielding, material purification and handling, or improved detector design. We explore these two possibilities in detail for semiconductor (Si and Ge) and Xe targets, considering several possibilities for the unmeasured ionization efficiency at low energies. For DM-electron-scattering searches, neutrinos start being an important background for exposures larger than ~1-10 kg-years in Si and Ge, and for exposures larger than ~0.1-1 kg-year in Xe. For the absorption of bosonic DM (dark photons and axion-like particles) by electrons, neutrinos are most relevant for masses below ~1 keV and again slightly more important in Xe. Treating the neutrinos as a signal, we find that the CNS of B-8 neutrinos can be observed with ~2 sigma significance with exposures of ~2, 7, and 20 kg-years in Xe, Ge, and Si, respectively, assuming there are no other backgrounds. We give an example for how this would constrain non-standard neutrino interactions. Neutrino components at lower energy can only be detected if the ionization efficiency is sufficiently large. In this case, observing pep neutrinos via CNS requires exposures ~10-100 kg-years in Si or Ge (~1000 kg-years in Xe), and observing CNO neutrinos would require an order of magnitude more exposure. Only Si could potentially detect Be-7 neutrinos. These measurements would allow for a direct measurement of the electron-neutrino survival probability over a wide energy range.

  • Type II Seesaw and tau lepton at the HL-LHC, HE-LHC and FCC-hh

    by: Li, Tong
    The tau lepton plays important role in distinguishing neutrino mass patterns and determining the chirality nature in heavy scalar mediated neutrino mass models, in the light of the neutrino oscillation experiments and its polarization measurement. We investigate the lepton flavor signatures with tau lepton at LHC upgrades, i.e. HL-LHC, HE-LHC and FCC-hh, through leptonic processes from doubly charged Higgs in the Type II Seesaw. We find that for the channel with one tau lepton in final states, the accessible doubly charged Higgs mass at HL-LHC can reach 655 GeV and 695 GeV for the neutrino mass patterns of normal hierarchy (NH) and inverted hierarchy (IH) respectively, with the luminosity of 3000 fb$^{-1}$. Higher masses, 975-1930 GeV for NH and 1035-2070 GeV for IH, can be achieved at HE-LHC and FCC-hh.

  • Review: Long-baseline oscillation experiments as a tool to probe High Energy Models

    by: Pasquini, Pedro
    We review the current status of neutrino oscillation experiments, mainly focussed on T2(H)K, NO$\nu$A and DUNE. Their capability to probe high energy physics is found in the precision measurement of the CP phase and $\theta_{23}$. In general, neutrino mass models predicts correlations among the mixing angles that can be used to scan and shrink down its parameter space. We updated previous analysis and presents a list of models that contain such structure.

  • Renormalization-Group Equations of Neutrino Masses and Flavor Mixing Parameters in Matter

    by: Xing, Zhi-zhong
    We borrow the general idea of renormalization-group equations (RGEs) to understand how neutrino masses and flavor mixing parameters evolve when neutrinos propagate in a medium, highlighting a meaningful possibility that the genuine flavor quantities in vacuum can be extrapolated from their matter-corrected counterparts to be measured in some realistic neutrino oscillation experiments. Taking the matter parameter $a \equiv 2\sqrt{2} \ G^{}_{\rm F} N^{}_e E$ to be an arbitrary scale-like variable with $N^{}_e$ being the net electron number density and $E$ being the neutrino beam energy, we derive a complete set of differential equations for the effective neutrino mixing matrix $V$ and the effective neutrino masses $\widetilde{m}^{}_i$ (for $i = 1, 2, 3$) without any {\it a priori} phase convention or assumption. In the standard parametrization of $V$ the RGEs for $\{\widetilde{\theta}^{}_{12}, \widetilde{\theta}^{}_{13}, \widetilde{\theta}^{}_{23}, \widetilde{\delta}\}$ in matter are presented. We demonstrate some useful differential invariants which retain the same form from vacuum to matter, including the well-known Naumov and Toshev relations. The RGEs of the partial $\mu$-$\tau$ asymmetries, the off-diagonal asymmetries and the sides of unitarity triangles of $V$ are also obtained as a by-product.

  • Right-Handed Neutrinos: DM and LFV $vs$ Collider
    Nuovo Cim. C40 (2017) 165

    by: Chekkal, Meziane
    In a class of neutrino mass models with a lepton flavor violation (LFV) Yukawa interaction term that involves a heavy right handed neutrino, a charged scalar and a charged lepton, we investigate at the ILC@500 GeV the possibility of observing news physics. These models can address neutrino mass and dark matter without being in conflict with different LFV constraints. By imposing DM relic density and LFV constraints, we recast the analysis done by L3 collaboration at LEP-II of monophoton searches on our space parameter and look for new physics in such channels like monophoton and $S S(\gamma)$, where we give different cuts and show the predicted distributions. We show also that using polarized beams could improve the statistical significance.

  • Proceedings, 31st Rencontres de Physique de La Vallée d'Aoste (La Thuile): La Thuile, Aosta , Italy, March 5-11, 2017
    Nuovo Cim. C40 (2018)

  • Neutrino masses in a model with one single basic neutrino

    by: Wang, Wen-ge
    We propose a model, in which there is only one basic species of neutrino. The three experimentally observed species of neutrino, namely, electron neutrino, muon neutrino, and tauon neutrino, are interpreted as composites of the basic neutrino and other particles. We study mass eigenstates of neutrino and derive approximate expressions for them. These approximate expressions predict a ratio of neutrino-mass difference, which is about half of the experimental result.

  • Linear stability analysis of collective neutrino oscillations without spurious modes
    Phys.Rev. D97 (2018) 023024

    by: Morinaga, Taiki (Waseda U.) et al.

    Collective neutrino oscillations are induced by the presence of neutrinos themselves. As such, they are intrinsically nonlinear phenomena and are much more complex than linear counterparts such as the vacuum or Mikheyev-Smirnov-Wolfenstein oscillations. They obey integro-differential equations, for which it is also very challenging to obtain numerical solutions. If one focuses on the onset of collective oscillations, on the other hand, the equations can be linearized and the technique of linear analysis can be employed. Unfortunately, however, it is well known that such an analysis, when applied with discretizations of continuous angular distributions, suffers from the appearance of so-called spurious modes: unphysical eigenmodes of the discretized linear equations. In this paper, we analyze in detail the origin of these unphysical modes and present a simple solution to this annoying problem. We find that the spurious modes originate from the artificial production of pole singularities instead of a branch cut on the Riemann surface by the discretizations. The branching point singularities on the Riemann surface for the original nondiscretized equations can be recovered by approximating the angular distributions with polynomials and then performing the integrals analytically. We demonstrate for some examples that this simple prescription does remove the spurious modes. We also propose an even simpler method: a piecewise linear approximation to the angular distribution. It is shown that the same methodology is applicable to the multienergy case as well as to the dispersion relation approach that was proposed very recently.

  • Decay of standard model-like Higgs boson $h\rightarrow \mu\tau$ in a 3-3-1 model with inverse seesaw neutrino masses

    by: Nguyen, T. Phong
    By adding new gauge singlets of neutral leptons, improved versions of the 3-3-1 models with right-handed neutrinos have been introduced recently to explain recent experimental data of neutrino oscillation through the inverse seesaw mechanism. We will prove that these models predict promising signals of lepton flavor violating decays of the standard model like-Higgs boson $h^0_1\rightarrow \mu\tau,e\tau$, which are suppressed in the original versions. One-loop contributions to these decay amplitudes are introduced in the unitary gauge. Based on numerical investigation, we find that the branching ratios decays $h^0_1\rightarrow\mu\tau,e\tau$ can reach values of $10^{-5}$ in the regions of the parameter space satisfying the current experimental data of the decay $\mu\rightarrow e\gamma$. The value of $10^{-4}$ appears when Yukawa couplings of leptons are close to the perturbative limit. Interesting properties of these regions of the parameter space are discussed.

  • Trimaximal mixing with a texture zero

    by: Gautam, Radha Raman
    We analyze neutrino mass matrices having one texture zero, assuming that the neutrino mixing matrix has either its first (TM$_1$) or second (TM$_2$) column identical to that of the tribimaximal mixing matrix. We found that all the six possible one texture zero neutrino mass matrices are compatible with the present neutrino oscillation data when combined TM$_1$ or TM$_2$ mixing. These textures have interesting predictions for the presently unknown parameters such as the effective Majorana neutrino mass, the Dirac CP violating phase and the neutrino mass scale. We also present a way to theoretically realize some of these textures using $A_4$ symmetry within the framework of type-I+II seesaw mechanism.

  • Lepton-Number-Charged Scalars and Neutrino Beamstrahlung

    by: Berryman, Jeffrey M.
    Experimentally, baryon number minus lepton number, $B-L$, appears to be a good global symmetry of nature. We explore the consequences of the existence of gauge-singlet scalar fields charged under $B-L$ -- dubbed lepton-number-charged scalars, LeNCS -- and postulate that these couple to the standard model degrees of freedom in such a way that $B-L$ is conserved even at the non-renormalizable level. In this framework, neutrinos are Dirac fermions. Including only the lowest mass-dimension effective operators, some of the LeNCS couple predominantly to neutrinos and may be produced in terrestrial neutrino experiments. We examine several existing constraints from particle physics, astrophysics, and cosmology to the existence of a LeNCS carrying $B-L$ charge equal to two, and discuss the emission of LeNCS's via "neutrino beamstrahlung," which occurs every once in a while when neutrinos scatter off of ordinary matter. We identify regions of the parameter space where existing and future neutrino experiments, including the Deep Underground Neutrino Experiment, are at the frontier of searches for such new phenomena.

  • Electric Dipole Moments in the Minimal Scotogenic Model

    by: Abada, Asmaa (Orsay, LPT) et al.

    In this work we consider a minimal version of the scotogenic model capable of accounting for an electron electric dipole moment within experimental sensitivity reach in addition to providing a dark matter candidate and radiatively generating neutrino masses. The Standard Model is minimally extended by two sterile fermions and one inert scalar doublet, both having odd parity, while the Standard Model particles have an even parity, imposed by a Z2 symmetry. The neutrino Yukawa couplings provide additional sources of CP violation, and thus a possible impact on electric dipole moments of charged leptons. This model provides two possible dark matter candidates (one bosonic and one fermionic) and our results show that, independently of the ordering of the generated light neutrino spectrum, one can have sizeable electron electron electric dipole moment within ACME sensitivity reach in the case of fermionic dark matter candidate.

  • Can an unbroken flavour symmetry provide an approximate description of lepton masses and mixing?

    by: Reyimuaji, Y. (ICTP, Trieste) et al.

    We provide a complete answer to the following question: what are the flavour groups and representations providing, in the symmetric limit, an approximate description of lepton masses and mixings? We assume that neutrinos masses are described by the Weinberg operator. We show that the pattern of lepton masses and mixings only depends on the dimension, type (real, pseudoreal, complex), and equivalence of the irreducible components of the flavour representation, and we find only six viable cases. In all cases the neutrinos are either anarchical or have an inverted hierarchical spectrum. In the context of SU(5) unification, only the anarchical option is allowed. Therefore, if the hint of a normal hierarchical spectrum were confirmed, we would conclude (under the above assumption) that symmetry breaking effects must play a primary role in the understanding of neutrino flavour observables. In order to obtain the above results, we develop a simple algorithm to determine the form of the lepton masses and mixings directly from the structure of the decomposition of the flavour representation in irreducible components, without the need to specify the form of the lepton mass matrices.

  • Three Neutrino Oscillations in Matter

    by: Ioannisian, Ara
    Following similar approaches in the past, the Schrodinger equation for three neutrino propagation in matter of constant density is solved analytically by two successive diagonalizations of 2x2 matrices. The final result for the oscillation probabilities is obtained directly in the conventional parametric form as in the vacuum but with explicit simple modification of two mixing angles ($\theta_{12}$ and $\theta_{13}$) and mass eigenvalues.

  • A topological approach to Neutrino masses by using exotic smoothness

    by: Asselmeyer-Maluga, T.
    In this paper, we will consider a cosmological model with two topological transitions of the space. The smooth 4-dimensional spacetime of the model admits topological transitions of its 3-dimensional slices. The whole approach is inspired by a class of exotic smoothness structure on $S^{3}\times\mathbb{R}$. In particular, this class of smoothness structures induces two topological transitions. Then, we are able to calculate the energy scales as associated to these topological transitions. For the first transition we will get the value of the GUT scale and the energy of the second transition is at the electroweak scale. The topology of of the exotic $S^{3}\times\mathbb{R}$ determines both, the energy of the scales by certain topological invariants, and the existence of the right-handed sterile neutrino. It is the input for the seesaw mechanism. Secondly, based on this model, we are able to calculate the Higgs and neutrino masses which are in a very good agreement with experiments. Finally, we give certain hints, again based on topology, why there are three generations of neutrinos and an asymmetry between neutrinos and anti-neutrinos. Furthermore we will identify a discrete symmetry group, the dihedral group, as acting on the generations.

  • Cosmologically Viable Low-energy Supersymmetry Breaking

    by: Hook, Anson (Maryland Center for Fundamental Physics, Department of Physics, University of Maryland) et al.

    A recent cosmological bound on the gravitino mass, $m_{3/2}<4.7$ eV, together with LHC results on the Higgs mass and direct searches, excludes minimal gauge mediation with high reheating temperatures. We discuss a minimal, vector-mediated model which incorporates the seesaw mechanism for neutrino masses, allows for thermal leptogenesis, ameliorates the $\mu$ problem, and achieves the observed Higgs mass and a gravitino as light as $1$-$2$ eV.

  • $ \mu-\tau $ Reflection Symmetry Embedded in Minimal Seesaw

    by: Nath, Newton
    We embed $\mu-\tau$ reflection symmetry into the minimal seesaw formalism, where two right-handed neutrinos are added to the Standard Model of particle physics. Assuming that both the left- and right-handed neutrino fields transform under $\mu-\tau$ reflection symmetry, we obtain the required forms of the neutrino Dirac mass matrix and the Majorana mass matrix for the right-handed neutrinos. To investigate the neutrino phenomenology at low energies, we first consider the breaking of $\mu-\tau$ reflection symmetry due to the renormalization group running, and then systematically study various breaking schemes by introducing explicit breaking terms at high energies.

  • Towards an effective theory of collective oscillations: Neutrino conversion in a neutrino flux

    by: Hansen, Rasmus S.L.
    Collective oscillations of supernova neutrinos above the neutrino sphere can be completely described by the propagation of individual neutrinos in external potentials and are in this sense a linear phenomenon. An effective theory of collective oscillations can be developed based on certain assumptions about time dependence of these potentials. General conditions for strong flavor transformations are formulated and these transformations can be interpreted as parametric resonance effects induced by periodic modulations of the potentials. A simplified and solvable example has been studied, where a probe neutrino is propagating in a flux of collinear neutrinos, such that $\nu \nu-$ interactions in the flux are absent. Properties of the parametric resonance are studied, and it is shown that integrations over energies and emission points of the flux neutrinos suppress modulations of the potentials and therefore strong transformations. The transformations are also suppressed by changes in densities of background neutrinos and electrons.

  • Neutrino masses in a conformal multi-Higgs-doublet model

    by: Fink, Manuel
    We construct a conformal version of a general multi-Higgs-doublet model with additional right-handed neutrino gauge-singlets. Assuming a minimal extension of the scalar sector by a real singlet field, we show that the resulting model achieves the same attractive properties as the non-conformal theory, combining the seesaw mechanism and higher-order mass production to generate naturally light neutrino masses. Starting with dimensionless couplings only, all masses and energy scales in the theory (including the heavy Majorana masses and the electroweak scale) are obtained from dimensional transmutation via the Coleman-Weinberg mechanism. A characteristic feature of the conformal model is the appearance of the scalon in the scalar spectrum.The mass of this particle, which can be expressed in terms of the masses of the other particles in the theory, is produced at the one-loop level. We establish a connection between the large seesaw scale and a suppression of the scalon interactions. The positivity condition for the squared scalon mass requires sufficiently large masses of the additional Higgs bosons balancing the contributions of the heavy neutrinos.

  • Theoretical Aspects of the Quantum Neutrino

    by: Parke, Stephen
    In this summary of my talk I will review the following the following three theoretical aspects of the quantum neutrino: current status, why we need precision measurements and neutrino oscillations amplitudes.

  • Neutrinos, supernovae, and the origin of the heavy elements
    Sci.China Phys.Mech.Astron. 61 (2018) 049501

    by: Qian, YongZhong (Minnesota U.)

    Stars of ~8-100 solar masses end their lives as core-collapse supernovae (SNe). In the process they emit a powerful burst of neutrinos, produce a variety of elements, and leave behind either a neutron star or a black hole. The wide mass range for SN progenitors results in diverse neutrino signals, explosion energies, and nucleosynthesis products. A major mechanism to produce nuclei heavier than iron is rapid neutron capture, or the r process. This process may be connected to SNe in several ways. A brief review is presented on current understanding of neutrino emission, explosion, and nucleosynthesis of SNe.

  • Neutrino motion and spin oscillations in magnetic field and matter currents

    by: Popov, Artem
    A brief review of a neutrino oscillations effect in an external magnetic field and matter currents is given. An ultra-relativistic neutrino propagation in moving external media is investigated. We have found a new spin operator which commutes with the corresponding Hamiltonian, exact wave functions and energy spectrum are obtained.

  • Neutrino quantum decoherence due to entanglement with magnetic field
    PoS (EPS-HEP 2017) 645

    by: Stankevich, Konstantin
    The phenomena of neutrino oscillations emerges due to coherent superposition of different neutrino states. The entanglement of neutrinos with its environment can lead to a suppression of neutrino oscillations. The master equation for neutrino evolution in a magnetic field is derived taking into account the entanglement with a magnetic field.

  • On possible application of spin light of neutrino in astrophysics

    by: Grigoriev, Alexander
    The $ spin $ $ light$ $ of $ $neutrino $ ($SL\nu$) is a phenomenon of electromagnetic radiation by a massive neutrino moving in external media that is originated owing to neutrino magnetic moment. In this short paper we note on the importance of this effect in the light of its connection with the neutrino magnetic moment, recap its basic properties in dense matter and give some general criteria for its best efficiency in nature. On this basis we propose a set of possible astrophysical environments where the $SL\nu$ can be manifested in principle.

  • Neutrino electromagnetic properties: a window to new physics - II

    by: Studenikin, Alexander
    There is merely a short note on the selected issues of neutrino electromagnetic properties with focus on effects of new physics. The meaning of "new physics" is twofold: 1) a massive neutrino have nonzero electromagnetic properties that can be considered as manifestation of new physics beyond the Standard Model, and 2) in studies of neutrinos electromagnetic interactions new effects are predicted that can lead to new phenomena accessible for observations.

  • Constraints on the sum of the neutrino masses in dynamical dark energy models with $w(z) \geq -1$ are tighter than those obtained in $\Lambda$CDM

    by: Vagnozzi, Sunny
    We explore cosmological constraints on the sum of the three active neutrino masses $M_{\nu}$ in the context of dynamical dark energy (DDE) models with equation of state (EoS) parametrized as a function of redshift $z$ by $w(z)=w_0+w_a\,z/(1+z)$, and satisfying $w(z)\geq-1$ for all $z$. We perform a Bayesian analysis and show that, within these models, the bounds on $M_{\nu}$ \textit{do not degrade} with respect to those obtained in the $\Lambda$CDM case; in fact the bounds are slightly tighter, despite the enlarged parameter space. We explain our results based on the observation that, for fixed choices of $w_0\,,w_a$ such that $w(z)\geq-1$ (but not $w=-1$ for all $z$), the upper limit on $M_{\nu}$ is tighter than the $\Lambda$CDM limit because of the well-known degeneracy between $w$ and $M_{\nu}$. The Bayesian analysis we have carried out then integrates over the possible values of $w_0$-$w_a$ such that $w(z)\geq-1$, all of which correspond to tighter limits on $M_{\nu}$ than the $\Lambda$CDM limit. We find a 95\% confidence level (C.L.) upper bound of $M_{\nu}<0.13\,\mathrm{eV}$. This bound can be compared with $M_{\nu}<0.16\,\mathrm{eV}$ at 95\%~C.L., obtained within the $\Lambda$CDM model, and $M_{\nu}<0.41\,\mathrm{eV}$ at 95\%~C.L., obtained in a DDE model with arbitrary EoS (which allows values of $w < -1$). Contrary to the results derived for DDE models with arbitrary EoS, we find that a dark energy component with $w(z)\geq-1$ is unable to alleviate the tension between high-redshift observables and direct measurements of the Hubble constant $H_0$. Finally, in light of the results of this analysis, we also discuss the implications for DDE models of a possible determination of the neutrino mass hierarchy by laboratory searches. (abstract abridged)

  • Hadronization via gravitational confinement
    J.Phys.Conf.Ser. 936 (2017) 012078

    by: Vayenas, C.G. (Patras U.) et al.

    We analyze baryogenesis using a Bohr-type rotating neutrino model in which the strong force is modeled as the gravitational force between ultrarelativistic neutrinos. The kinetic energy plus rest energy of these neutrinos constitutes the rest energy of the gravitationally confined composite neutrino structure. In this work we derive a simple expression for the gravitational mass of the rotating neutrinos in terms of their rest mass and their total energy. It is found, both analytically and graphically, that when the gravitational mass reaches the Planck mass, then the relativistic mass of the neutrinos equals the effective mass of u and d quarks. The model contains no adjustable parameters and leads to semiquantitative (within 1%) agreement with the masses of baryons. It also shows that hadronization is easier to achieve with light particles such as neutrinos rather than with heavier particles. The model can also be extended by considering ultrarelavivistic rotating positron or electron-neutrino pairs, triplets or quartets whose mass is found to match within 2% those of W±, Z° and H° bosons.

  • QED Plasma at High Temperature

    by: Masood, Samina S.
    We demonstrate that the early universe behaved as a relativistic QED (Quantum Electrodynamics) plasma around the nucleosynthesis time while the temperature of the universe was below the neutrino decoupling temperature in the early universe. QED coupling constant becomes a temperature dependent parameter due to the radiative corrections to vacuum polarization in the early universe at nucleosynthesis temperature. Renormalization scheme of QED is used to calculate the effective parameters of relativistic plasma in the early universe. Renormalization constants of QED serve as effective parameters of the theory and are used to determine the behavior of matter. We explicitly compute the parameters of QED plasma such as Debye length and the plasma frequency as a function of temperature. Light is slowed down and trapped due to bending in such a medium and the frequency of electromagnetic radiation becomes a function of temperature as well.

  • Matter-neutrino resonance in a multi-angle neutrino bulb model

    by: Vlasenko, A.
    Simulations of neutrino flavor evolution in compact merger environments have shown that neutrino flavor, and hence nucleosynthesis, can be strongly affected by the presence of matter-neutrino resonances (MNRs), where there is a cancelation between the matter and the neutrino potential. Simulations performed thus far follow flavor evolution along a single neutrino trajectory, but self-consistency requires all trajectories to be treated simultaneously, and it has not been known whether MNR phenomena would still occur in multi-angle models. In this paper, we present the first fully multi-angle calculations of MNR. We find that familiar MNR phenomena, where neutrinos transform to a greater extent than anti-neutrinos and a feedback mechanism maintains the cancellation between the matter and neutrino potential, still occurs for a subset of angular bins, although the flavor transformation is not as efficient as in the single-angle case. In addition, we find other types of flavor transformation that are not seen in single-angle simulations. These flavor transformation phenomena appear to be robust and are present for a wide range of model parameters, as long as an MNR is present. Although computational constraints currently limit us to models with spherical symmetry, our results suggest that the presence of an MNR generally leads to large-scale neutrino flavor evolution in multi-angle systems.

  • Charged Lepton Flavor Violation in a class of Radiative Neutrino Mass Generation Models

    by: Chowdhury, Talal Ahmed
    We investigate charged lepton flavor violating processes $\mu\rightarrow e \gamma$, $\mu\rightarrow e e \overline{e}$ and $\mu-e$ conversion in nuclei for a class of three-loop radiative neutrino mass generation models with electroweak multiplets of increasing order. We find that, because of certain cancellations among various one-loop diagrams which give the dipole and non-dipole contributions in effective $\mu e \gamma$ vertex and Z-penguin contribution in effective $\mu e Z$ vertex, the flavor violating processes $\mu\rightarrow e\gamma$ and $\mu-e$ conversion in nuclei become highly suppressed compared to $\mu\rightarrow e e \overline{e}$ process. Therefore, the observation of such pattern in LFV processes may reveal the radiative mechanism behind neutrino mass generation.

  • Majorana neutrino and the vacuum of Bogoliubov quasiparticle

    by: Fujikawa, Kazuo
    The Lagrangian of the seesaw mechanism is C violating but the same Lagrangian when re-written in terms of Majorana neutrinos is manifestly C invariant. To resolve this puzzling feature, a relativistic analogue of Bogoliubov transformation, which preserves CP but explicitly breaks C and P separately, was introduced together with the notions of a Bogoliubov quasiparticle and an analogue of the energy gap in BCS theory. The idea of Majorana neutrino as Bogoliubov quasiparticle was then suggested. In this paper, we study the vacuum structure of the Bogoliubov quasiparticle which becomes heavy by absorbing the C-breaking. By treating an infinitesimally small C violating term as an analogue of the chiral symmetry breaking nucleon mass in the model of Nambu and Jona-Lasinio, we construct an explicit form of the vacuum of the Bogoliubov quasiparticle which defines Majorana neutrinos in seesaw mechanism. The vacuum of the Bogoliubov quasiparticle thus constructed has an analogous condensate structure as the vacuum of the quasiparticle (nucleon) in the Nambu--Jona-Lasinio model.

  • Neutrino-nucleon scattering in the neutrino-sphere

    by: Bedaque, Paulo F.
    We calculate the differential scattering rate for thermal neutrinos in a hot and dilute gas of interacting neutrons using linear response theory. The dynamical structure factors for density and spin fluctuations of the strongly interacting neutron matter, expected in the neutrino decoupling regions of supernovae and neutron star mergers, are calculated in the virial expansion for the first time. Correlations due to nucleon-nucleon interactions are taken into account using a pseudo-potential that reproduces measured nucleon-nucleon phase shifts, and we find that attractive s-wave interactions enhance the density response and suppress the spin response of neutron matter. The net effect of neutron correlations is to strongly suppress backscattering. Moreover, we find nearly exact scaling laws for the response functions, valid for the range $T = 5 - 10$ MeV and q < 30 MeV, allowing us to obtain analytic results for the dynamic structure factors at second-order in the fugacity of the neutron gas. We find that the modification of scattering rates depends on the energy and momentum exchanged, implying that dynamical structure factors are essential to describe neutrino decoupling in supernovae and neutron star mergers.

  • The next-to-leading order QCD and electroweak corrections to the Higgs-strahlung processes

    by: Obul, Pazilet
    In this paper we calculate the total and fiducial cross sections as well as differential distributions for the Higgs-strahlung or VH process $p p \to VH \to l\nu_l/l^- l^+ + H$, (V = W or Z ) including QCD and electro-weak corrections up to next-to-leading order by using the before and after reweighting photon PDFs of NNPDF2.3qed,NNPDF3.0qed, MRST2004qed, CT14QEDinc, and LUXqed at the LHC with 13 TeV and Higgs-boson mass $\ M_{H}=125$ GeV. The predictions from the various photon PDFs before and after reweighting against each other are in good agreement. The photon PDF uncertainties of the photon induced cross sections decrease significantly with the reweighting-PDFs.

  • The longitudinal leading-twist distribution amplitude of $J/\psi$ meson within background field theory

    by: Fu, Hai-Bing
    We make a detailed study on the $J/\psi$ meson longitudinal leading-twist distribution amplitude $\phi_{2;J/\psi}^\|$ by using the QCD sum rules within the background field theory. By keeping all the non-perturbative condensates up to dimension-six, we obtain accurate QCD sum rules for the moments $\langle\xi_{n;J/\psi}^\|\rangle$. The first three ones are $\langle\xi_{2;J/\psi}^\|\rangle=0.083(12)$, $\langle\xi_{4;J/\psi}^\|\rangle=0.015(5)$ and $\langle\xi_{6;J/\psi}^\|\rangle=0.003(2)$, leading to a single peaked behavior for $\phi_{2;J/\psi}^\|$ which is sharper than the previous ones around the region of $x\sim0.5$. As an application, we adopt the QCD light-cone sum rules to calculate the $B_c$ meson semileptonic decay $B_c^+ \to J/\psi \ell^+ \nu_\ell$. We obtain $\Gamma(B_c^+ \to J/\psi \ell^+ \nu_\ell) = (89.67^{+24.76}_{-19.06}) \times 10^{-15}~{\rm GeV}$ and $\Re(J/\psi \ell^+ \nu_\ell) = 0.217^{+0.069}_{-0.057}$, which agree with the next-to-leading order pQCD prediction and the new CDF measurement within errors.

  • Self-interacting dark matter constraints in a thick dark disk scenario

    by: Vattis, Kyriakos (Brown U.) et al.

    A thick dark matter disk is predicted in cold dark matter simulations as the outcome of the interaction between accreted satellites and the stellar disk in Milky Way sized halos. We study the effects of a self-interacting thick dark disk on the energetic neutrino flux from the Sun. We find that for particle masses between 100 GeV and 1 TeV and dark matter annihilation to heavy leptons either the self-interaction may not be strong enough to solve the small scale structure motivation or a dark disk cannot be present in the Milky Way.

  • Top quark modelling in POWHEG BOX
    ZU TH 03/18

    by: Ježo, Tomáš
    We review recent theoretical improvements of Monte Carlo event generators for top-quark pair production and decay at the LHC based on the POWHEG method. We present an event generator that implements spin correlations and off-shell effects in top-decay chains described in terms of exact matrix elements for $pp\to \ell^+\nu_{\ell}\, l^-\bar{\nu}_{l} \,b \,\bar b$ at order $\alpha^4 \alpha_s^2$, including full NLO QCD corrections and interference effects with single-top and non-resonant topologies yielding to the same final state. We then compare its predictions to previous generators that implement NLO corrections only in the top-pair production dynamics. We consider the mass distributions of the $Wj_{\rm B}$ and $\ell j_{\rm B}$ systems, proxies for direct top-mass determinations, and jet-vetoed cross section, a probe of the $Wt$ single top contribution.

  • Addendum to "Compact Perturbative Expressions for Neutrino Oscillations in Matter"

    by: Denton, Peter B. (Bohr Inst.) et al.

    In this paper we rewrite the neutrino mixing angles and mass squared differences in matter given, in our original paper, in a notation that is more conventional for the reader. Replacing the usual neutrino mixing angles and mass squared differences in the expressions for the vacuum oscillation probabilities with these matter mixing angles and mass squared differences gives an excellent approximation to the oscillation probabilities in matter. Comparisons for T2K, NOvA, T2HKK and DUNE are also given for neutrinos and anti-neutrinos, disappearance and appearance channels, normal ordering and inverted ordering.

  • Probing the Seesaw Mechanism and Leptogenesis with the International Linear Collider

    by: Antusch, Stefan
    We investigate the potential of the International Linear Collider (ILC) to probe the mechanisms of neutrino mass generation and leptogenesis within the minimal seesaw model. Our results can also be used as an estimate for the potential of a Compact Linear Collider (CLIC). We find that heavy sterile neutrinos that simultaneously explain both, the observed light neutrino oscillations and the baryon asymmetry of the universe, can be found in displaced vertex searches at ILC. We further study the precision at which the flavour-dependent active-sterile mixing angles can be measured. The measurement of the ratios of these mixing angles, and potentially also of the heavy neutrino mass splitting, can test whether minimal type I seesaw models are the origin of the light neutrino masses, and it can be a first step towards probing leptogenesis as the mechanism of baryogenesis. Our results show that the ILC can be used as a discovery machine for New Physics in feebly coupled sectors that can address fundamental questions in particle physics and cosmology.

  • Model-Independent $\bar\nu_{e}$ Short-Baseline Oscillations from Reactor Spectral Ratios

    by: Gariazzo, S.
    We consider the ratio of the spectra measured in the DANSS neutrino experiment at 12.7 and 10.7~m from a nuclear reactor. These data give a new model-independent indication in favor of short-baseline $\bar\nu_{e}$ oscillations which reinforce the model-independent indication found in the late 2016 in the NEOS experiment. The combined analysis of the NEOS and DANSS spectral ratios in the framework of 3+1 active-sterile neutrino mixing favor short-baseline $\bar\nu_{e}$ oscillations with a statistical significance of $3.7\sigma$. The two mixing parameters $\sin^{2}2\vartheta_{ee}$ and $\Delta{m}^{2}_{41}$ are constrained at $2\sigma$ in a narrow-$\Delta{m}^{2}_{41}$ island at $\Delta{m}^2_{41} \simeq 1.3 \, \text{eV}^2$, with $ \sin^{2}2\vartheta_{ee} = 0.049 \pm 0.023 $ ($2\sigma$). We discuss the implications of the model-independent NEOS+DANSS analysis for the reactor and Gallium anomalies. The NEOS+DANSS model-independent determination of short-baseline $\bar\nu_{e}$ oscillations allows us to analyze the reactor rates without assumptions on the values of the main reactor antineutrino fluxes and the data of the Gallium source experiments with free detector efficiencies. The corrections to the reactor neutrino fluxes and the Gallium detector efficiencies are obtained from the fit of the data. In particular, we confirm the indication in favor of the need for a recalculation of the $^{235}\text{U}$ reactor antineutrino flux found in previous studies assuming the absence of neutrino oscillations.

  • Galaxy Formation in Sterile Neutrino Dark Matter Models
    Astrophys.J. 854 (2018) 1

    by: Menci, N. (Rome Observ.) et al.

    We investigate galaxy formation in models with dark matter (DM) constituted by sterile neutrinos. Given their large parameter space, defined by the combinations of sterile neutrino mass $m_{\nu}$ and mixing parameter $\sin^2(2\theta)$ with active neutrinos, we focus on models with $m_{\nu}=7$ keV, consistent with the tentative 3.5 keV line detected in several X-ray spectra of clusters and galaxies. We consider i) two resonant production models with $\sin^2(2\theta)=5\,10^{-11}$ and $\sin^2(2\theta)=2\,10^{-10}$, to cover the range of mixing parameter consistent with the 3.5 keV line; ii) two scalar-decay models, representative of the two possible cases characterizing such a scenario: a freeze-in and a freeze-out case. We also consider thermal Warm Dark Matter with particle mass $m_X=3$ keV. Using a semi-analytic model, we compare the predictions for the different DM scenarios with a wide set of observables. We find that comparing the predicted evolution of the stellar mass function, the abundance of satellites of Milky Way-like galaxies, and the global star formation history of galaxies with observations does not allow to disentangle the effects of the baryonic physics from those related to the different DM models. On the other hand, the distribution of the stellar-to-halo mass ratios, the abundance of faint galaxies in the UV luminosity function at $z\gtrsim 6$, and the specific star formation and age distribution of local, low-mass galaxies constitute potential probes for the considered DM scenarios. We discuss how next observations with upcoming facilities will enable to rule out or to strongly support DM models based on sterile neutrinos.

  • On the mass and thermodynamics of the Higgs boson
    Physica A492 (2018) 737-746

    by: Fokas, A.S. (Cambridge U., DAMTP) et al.

    In two recent works we have shown that the masses of the W ± and Z o bosons can be computed from first principles by modeling these bosons as bound relativistic gravitationally confined rotational states consisting of e ±–νe pairs in the case of W ± bosons and of a e+–νe–e− triplet in the case of the Z o boson. Here, we present similar calculations for the Higgs boson which we model as a bound rotational state consisting of a positron, an electron, a neutrino and an antineutrino. The model contains no adjustable parameters and the computed boson mass of 125.7 GeV/c 2 , is in very good agreement with the experimental value of 125.1 ± 1 GeV/c 2 . The thermodynamics and potential connection of this particle with the Higgs field are also briefly addressed.

  • Texture zeros and hierarchical masses from flavour (mis)alignment
    Nucl.Phys. B928 (2018) 535-554

    by: Hollik, Wolfgang G. (DESY) et al.

    We introduce an unconventional interpretation of the fermion mass matrix elements. As the full rotational freedom of the gauge-kinetic terms renders a set of infinite bases called weak bases, basis-dependent structures as mass matrices are unphysical. Matrix invariants, on the other hand, provide a set of basis-independent objects which are of more relevance. We employ one of these invariants to give a new parametrization of the mass matrices. By virtue of it, one gains control over its implicit implications on several mass matrix structures. The key element is the trace invariant which resembles the equation of a hypersphere with a radius equal to the Frobenius norm of the mass matrix. With the concepts of alignment or misalignment we can identify texture zeros with certain alignments whereas Froggatt-Nielsen structures in the matrix elements are governed by misalignment. This method allows further insights of traditional approaches to the underlying flavour geometry.

  • Leptogenesis from Heavy Right-Handed Neutrinos in CPT Violating Backgrounds
    Eur.Phys.J. C78 (2018) 113

    by: Bossingham, Thomas (King's Coll. London) et al.

    We discuss leptogenesis in a model with heavy right-handed Majorana neutrinos propagating in a constant but otherwise generic CPT-violating axial time-like background (which could be motivated by string theory considerations). At temperatures much higher than the temperature of the electroweak phase transition we solve analytically but approximately (using Pade approximants) the corresponding Boltzmann equations, which describe lepton asymmetry generation due to the tree-level decays of the heavy neutrinos into standard model leptons. These leptons are effectively massless at such temperatures. The current work completes in a rigorous way a preliminary treatment of the same system, by some of the present authors. In this earlier work, lepton asymmetry was crudely estimated considering the decay of a right-handed neutrino at rest. Our present analysis includes thermal momentum modes for the heavy neutrino and this leads to a total lepton asymmetry which is bigger by a factor of two as compared to the previous estimate. Nevertheless, our current and preliminary results for the freezeout are found to be in agreement (within a 12.5% uncertainty). Our analysis depends on a novel use of Pade approximants to solve the Boltzmann equations and may be more widely useful in cosmology.

  • Radiative neutrino masses from order-4 CP symmetry
    JHEP 1802 (2018) 025

    by: Ivanov, Igor P. (Lisbon, CFTP)

    Generalized CP symmetry of order 4 (CP4) is surprisingly powerful in shaping scalar and quark sectors of multi-Higgs models. Here, we extend this framework to the neutrino sector. We build two simple Majorana neutrino mass models with unbroken CP4, which are analogous to Ma's scotogenic model. Both models use three Higgs doublets and two or three right-handed (RH) neutrinos. The minimal CP4 symmetric scotogenic model uses only two RH neutrinos, leads to three non-zero light neutrino masses, and contains a built-in mechanism to further suppress them via phase alignment. With three RH neutrinos, one generates a type I seesaw mass matrix of rank 1, which is then corrected by the same scotogenic mechanism, naturally leading to two mass scales for neutrino masses. These minimal CP4-based constructions emerge as a primer for introducing additional symmetry structures and exploring their phenomenological consequences.

  • Scalar dark matter, Type II Seesaw and the DAMPE cosmic ray $e^+ + e^-$ excess
    Phys.Lett. B779 (2018) 130-135

    by: Li, Tong (ARC, CoEPP, Melbourne) et al.

    The DArk Matter Particle Explorer (DAMPE) has reported a measurement of the flux of high energy cosmic ray electrons plus positrons (CREs) in the energy range between $25$ GeV and $4.6$ TeV. With unprecedented high energy resolution, the DAMPE data exhibit an excess of the CREs flux at an energy of around $1.4$ TeV. In this letter, we discuss how the observed excess can be understood in a minimal framework where the Standard Model (SM) is supplemented by a stable SM singlet scalar as dark matter (DM) and type II seesaw for generating the neutrino mass matrix. In our framework, a pair of DM particles annihilates into a pair of the SM SU(2) triplet scalars ($\Delta$s) in type II seesaw, and the subsequent $\Delta$ decays create the primary source of the excessive CREs around $1.4$ TeV. The lepton flavor structure of the primary source of CREs has a direct relationship with the neutrino oscillation data. We find that the DM interpretation of the DAMPE excess determines the pattern of neutrino mass spectrum to be the inverted hierarchy type, taking into account the constraints from the Fermi-LAT observations of dwarf spheroidal galaxies.

  • Testing a lepton quarticity flavor theory of neutrino oscillations with the DUNE experiment
    Phys.Lett. B778 (2018) 459-463

    by: Srivastava, Rahul (Valencia U., IFIC) et al.

    Oscillation studies play a central role in elucidating at least some aspects of the flavor problem. Here we examine the status of the predictions of a lepton quarticity flavor theory of neutrino oscillations against the existing global sample of oscillation data. By performing quantitative simulations we also determine the potential of the upcoming DUNE experiment in narrowing down the currently ill-measured oscillation parameters $\theta_{23}$ and $\delta_{\text{CP}}$. We present the expected improved sensitivity on these parameters for different assumptions.

  • Lepton universality violation and right-handed currents in $b \to c \tau \nu$
    Phys.Lett. B779 (2018) 52-57

    by: He, Xiao-Gang (Taiwan, Natl. Taiwan U.) et al.

    We consider the recent LHCb result for $B_c\to J/\psi \tau \nu$ in conjunction with the existing anomalies in $R(D)$ and $R(D^\star)$ within the framework of a right-handed current with enhanced couplings to the third generation. The model predicts a linear relation between the observables and their SM values in terms of two combinations of parameters. The strong constraints from $b\to s \gamma$ on $W-W^\prime$ mixing effectively remove one of the combinations of parameters resulting in an approximate proportionality between all three observables and their SM values. To accommodate the current averages for $R(D)$ and $R(D^\star)$, the $W^\prime$ mass should be near 1 TeV, and possibly accessible to direct searches at the LHC. In this scenario we find that $R(J/\psi)$ is enhanced by about 20\% with respect to its SM value and about 1.5$\sigma$ below the central value of the LHCb measurement. The predicted $d\Gamma/dq^2$ distribution for $B\to D(D^\star) \tau \nu$ is in agreement with the measurement and the model satisfies the constraint from the $B_c$ lifetime.

  • GeV-scale hot sterile neutrino oscillations: a numerical solution
    JHEP 1802 (2018) 078

    by: Ghiglieri, J. (CERN) et al.

    The scenario of baryogenesis through GeV-scale sterile neutrino oscillations is governed by non-linear differential equations for the time evolution of a sterile neutrino density matrix and Standard Model lepton and baryon asymmetries. By employing up-to-date rate coefficients and a non-perturbatively estimated Chern-Simons diffusion rate, we present a numerical solution of this system, incorporating the full momentum and helicity dependences of the density matrix. The density matrix deviates significantly from kinetic equilibrium, with the IR modes equilibrating much faster than the UV modes. For equivalent input parameters, our final results differ moderately (~50%) from recent benchmarks in the literature. The possibility of producing an observable baryon asymmetry is nevertheless confirmed. We illustrate the dependence of the baryon asymmetry on the sterile neutrino mass splitting and on the CP-violating phase measurable in active neutrino oscillation experiments.

  • Neutrino Mass Priors for Cosmology from Random Matrices
    Phys.Rev. D97 (2018) 043510

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

    Cosmological measurements of structure are placing increasingly strong constraints on the sum of the neutrino masses, $\Sigma m_\nu$, through Bayesian inference. Because these constraints depend on the choice for the prior probability $\pi(\Sigma m_\nu)$, we argue that this prior should be motivated by fundamental physical principles rather than the ad hoc choices that are common in the literature. The first step in this direction is to specify the prior directly at the level of the neutrino mass matrix $M_\nu$, since this is the parameter appearing in the Lagrangian of the particle physics theory. Thus by specifying a probability distribution over $M_\nu$, and by including the known squared mass splittings, we predict a theoretical probability distribution over $\Sigma m_\nu$ that we interpret as a Bayesian prior probability $\pi(\Sigma m_\nu)$. We find that $\pi(\Sigma m_\nu)$ peaks close to the smallest $\Sigma m_\nu$ allowed by the measured mass splittings, roughly $0.06 \, {\rm eV}$ ($0.1 \, {\rm eV}$) for normal (inverted) ordering, due to the phenomenon of eigenvalue repulsion in random matrices. We consider three models for neutrino mass generation: Dirac, Majorana, and Majorana via the seesaw mechanism; differences in the predicted priors $\pi(\Sigma m_\nu)$ allow for the possibility of having indications about the physical origin of neutrino masses once sufficient experimental sensitivity is achieved. We present fitting functions for $\pi(\Sigma m_\nu)$, which provide a simple means for applying these priors to cosmological constraints on the neutrino masses or marginalizing over their impact on other cosmological parameters.

  • Gravitational Leptogenesis, Reheating, and Models of Neutrino Mass
    Phys.Rev. D97 (2018) 043511

    by: Adshead, Peter (Illinois U., Urbana) et al.

    Gravitational leptogenesis refers to a class of baryogenesis models in which the matter-antimatter asymmetry of the universe arises through the standard model lepton-number gravitational anomaly. In these models chiral gravitational waves source a lepton asymmetry in standard model neutrinos during the inflationary epoch. We point out that gravitational leptogenesis can be successful in either the Dirac or Majorana neutrino mass scenario. In the Dirac mass scenario, gravitational leptogenesis predicts a relic abundance of sterile neutrinos that remain out of equilibrium, and the lepton asymmetry carried by the standard model sector is unchanged. In the Majorana mass scenario, the neutrinos participate in lepton-number-violating interactions that threaten to washout the lepton asymmetry during post-inflationary reheating. However, we show that a complete (exponential) washout of the lepton asymmetry is prevented if the lepton-number-violating interactions go out of equilibrium before all of the standard model Yukawa interactions come into equilibrium. The baryon and lepton asymmetries carried by right-chiral quarks and leptons are sequestered from the lepton-number violation, and the washout processes only suppress the predicted baryon asymmetry by a factor of $\varepsilon_{\rm w.o.} = \pm O(0.1)$. The sign of $\varepsilon_{\rm w.o.}$ depends on the model parameters in such a way that a future measurement of the primordial gravitational wave chirality would constrain the scale of lepton-number violation (heavy Majorana neutrino mass).

  • Neutrino CP violation and sign of baryon asymmetry in the minimal seesaw model
    Phys.Lett. B778 (2018) 6-16

    by: Shimizu, Yusuke (Hiroshima U.) et al.

    We discuss the correlation between the CP violating Dirac phase of the lepton mixing matrix and the cosmological baryon asymmetry based on the leptogenesis in the minimal seesaw model with two right-handed Majorana neutrinos and the trimaximal mixing for neutrino flavors. The sign of the CP violating Dirac phase at low energy is fixed by the observed cosmological baryon asymmetry since there is only one phase parameter in the model. According to the recent T2K and NO ν A data of the CP violation, the Dirac neutrino mass matrix of our model is fixed only for the normal hierarchy of neutrino masses.

  • Accelerator and reactor complementarity in coherent neutrino scattering
    Phys.Rev. D97 (2018) 035009

    by: Dent, James B. (Sam Houston State U.) et al.

    We study the complementarity between accelerator and reactor coherent elastic neutrino-nucleus elastic scattering (CE$\nu$NS) experiments for constraining new physics in the form of non-standard neutrino interactions (NSI). Firstly, considering just data from the recent observation by the COHERENT experiment, we explore interpretive degeneracies that emerge when activating either two or four unknown NSI parameters. Next, we demonstrate that simultaneous treatment of reactor and accelerator experiments, each employing at least two distinct target materials, can break a degeneracy between up and down flavor-diagonal NSI terms that survives analysis of neutrino oscillation experiments. Considering four flavor-diagonal ($ee/\mu\mu$) up and down-type NSI parameters, we find that all terms can be measured with high local precision (to a width as small as $\sim$5\% in Fermi units) by next-generation experiments, although discrete reflection ambiguities persist.

  • Single pion production in neutrino-nucleon Interactions
    Phys.Rev. D97 (2018) 013002

    by: Kabirnezhad, Monireh (NCBJ, Swierk)

    This work represents an extension of the single pion production model proposed by Rein [Z. Phys. C 35, 43 (1987).ZPCFD20170-973910.1007/BF01561054]. The model consists of resonant pion production and nonresonant background contributions coming from three Born diagrams in the helicity basis. The new work includes lepton mass effects, and nonresonance interaction is described by five diagrams based on a nonlinear σ model. This work provides a full kinematic description of single pion production in the neutrino-nucleon interactions, including resonant and nonresonant interactions in the helicity basis, in order to study the interference effect.

  • Non-standard interactions and neutrinos from dark matter annihilation in the Sun
    JCAP 1802 (2018) 001

    by: Demidov, S.V. (Moscow, INR)

    We perform an analysis of the influence of non-standard neutrino interactions (NSI) on neutrino signal from dark matter annihilations in the Sun. Taking experimentally allowed benchmark values for the matter NSI parameters we show that the evolution of such neutrinos with energies at GeV scale can be considerably modified. We simulate propagation of neutrinos from the Sun to the Earth for realistic dark matter annihilation channels and find that the matter NSI can results in at least 30% correction to the signal rate of muon track events at neutrino telescopes. At the same time electron neutrino flux from dark matter annihilation in the Sun can be changed by a factor of few.

  • Explaining the 3.5 keV X-ray Line in a ${L_{\mu}-L_{\tau}}$ Extension of the Inert Doublet Model
    JCAP 1802 (2018) 002

    by: Biswas, Anirban (Harish-Chandra Res. Inst.) et al.

    We explain the existence of neutrino masses and their flavour structure, dark matter relic abundance and the observed 3.5 keV X-ray line within the framework of a gauged U(1)Lμ − Lτ extension of the "scotogenic" model. In the U(1)Lμ − Lτ symmetric limit, two of the RH neutrinos are degenerate in mass, while the third is heavier. The U(1)Lμ − Lτ symmetry is broken spontaneously. Firstly, this breaks the μ−τ symmetry in the light neutrino sector. Secondly, this results in mild splitting of the two degenerate RH neutrinos, with their mass difference given in terms of the U(1)Lμ − Lτ breaking parameter. Finally, we get a massive Zμτ gauge boson. Due to the added Z2 symmetry under which the RH neutrinos and the inert doublet are odd, the canonical Type-I seesaw is forbidden and the tiny neutrino masses are generated radiatively at one loop. The same Z2 symmetry also ensures that the lightest RH neutrino is stable and the other two can only decay into the lightest one. This makes the two nearly-degenerate lighter neutrinos a two-component dark matter, which in our model are produced by the freeze-in mechanism via the decay of the Zμτ gauge boson in the early universe. We show that the next-to-lightest RH neutrino has a very long lifetime and decays into the lightest one at the present epoch explaining the observed 3.5 keV line.

  • Neutrino propagation in binary neutron star mergers in presence of nonstandard interactions
    Phys.Rev. D97 (2018) 023014

    by: Chatelain, Amélie (APC, Paris) et al.

    We explore the impact of nonstandard interactions on neutrino propagation in accretion disks around binary neutron star merger remnants. We show flavor evolution can be significantly modified even for values of the nonstandard couplings well below current bounds. We demonstrate the occurrence of inner resonances as synchronized MSW phenomena and show that intricate conversion patterns might appear depending on the nonstandard interaction parameters. We discuss the possible implications for nucleosynthesis.

  • Texture Zero Neutrino Models and Their Connection with Resonant Leptogenesis
    Nucl.Phys. B929 (2018) 21-57

    by: Achelashvili, Avtandil (Ilia State U.) et al.

    Within the low scale resonant leptogenesis scenario, the cosmological CP asymmetry may arise by radiative corrections through the charged lepton Yukawa couplings. While in some cases, as one expects, decisive role is played by the $\lambda_{\tau }$ coupling, we show that in specific neutrino textures only by inclusion of the $\lambda_{\mu }$ the cosmological CP violation is generated at 1-loop level. With the purpose to relate the cosmological CP violation to the leptonic CP phase $\delta $, we consider an extension of MSSM with two right handed neutrinos (RHN), which are degenerate in mass at high scales. Together with this, we first consider two texture zero 3x2 Dirac Yukawa matrices of neutrinos. These via see-saw generated neutrino mass matrices augmented by single $\Delta L=2$ dimension five (d=5) operator give predictive neutrino sectors with calculable CP asymmetries. The latter is generated through $\lambda_{\mu , \tau }$ coupling(s) at 1-loop level. Detailed analysis of the leptogenesis is performed. We also revise some one texture zero Dirac Yukawa matrices, considered earlier, and show that addition of a single $\Delta L=2$, d=5 entry in the neutrino mass matrices, together with newly computed 1-loop corrections to the CP asymmetries, give nice accommodation of the neutrino sector and desirable amount of the baryon asymmetry via the resonant leptogenesis even for rather low RHN masses (~few TeV - $10^7$ GeV).

  • Left-handed and right-handed U(1) gauge symmetry
    JHEP 1801 (2018) 099

    by: Nomura, Takaaki (Korea Inst. Advanced Study, Seoul) et al.

    We propose a model with the left-handed and right-handed continuous Abelian gauge symmetry, U(1)$_{L}$ × U(1)$_{R}$ . Then three right-handed neutrinos are naturally required to achieve U(1)$_{R}$ anomaly cancellations, while several mirror fermions are also needed to do U(1)$_{L}$ anomaly cancellations. Then we formulate the model, and discuss its testability of the new gauge interactions at collider physics such as the large hadron collider (LHC) and the international linear collider (ILC). In particular, we can investigate chiral structure of the interactions by the analysis of forward-backward asymmetry based on polarized beam at the ILC.

  • Detecting a heavy neutrino electric dipole moment at the LHC
    Phys.Lett. B777 (2018) 246-249

    by: Sher, Marc (William-Mary Coll.) et al.

    The milliQan Collaboration has proposed to search for millicharged particles by looking for very weakly ionizing tracks in a detector installed in a cavern near the CMS experiment at the LHC. We note that another form of exotica can also yield weakly ionizing tracks. If a heavy neutrino has an electric dipole moment (EDM), then the milliQan experiment may be sensitive to it as well. In particular, writing the general dimension-5 operator for an EDM with a scale of a TeV and a one-loop factor, one finds a potential EDM as high as a few times 10 −17 e-cm, and models exist where it is an order of magnitude higher. Redoing the Bethe calculation of ionization energy loss for an EDM, it is found that the milliQan detector is sensitive to EDMs as small as 10 −17 e-cm. Using the production cross-section and analyzing the acceptance of the milliQan detector, we find the expected 95% exclusion and 3 σ sensitivity over the range of neutrino masses from 5–1000 GeV for integrated luminosities of 300 and 3000 fb −1 at the LHC.

  • LHC signals of radiatively-induced neutrino masses and implications for the Zee-Babu model
    Phys.Lett. B779 (2018) 107-116

    by: Alcaide, Julien (Valencia U.) et al.

    Contrary to the see-saw models, extended Higgs sectors leading to radiatively-induced neutrino masses do require the extra particles to be at the TeV scale. However, these new states have often exotic decays, to which experimental LHC searches performed so far, focused on scalars decaying into pairs of same-sign leptons, are not sensitive. In this paper we show that their experimental signatures can start to be tested with current LHC data if dedicated multi-region analyses correlating different observables are used. We also provide high-accuracy estimations of the complicated Standard Model backgrounds involved. For the case of the Zee-Babu model, we show that regions not yet constrained by neutrino data and low-energy experiments can be already probed, while most of the parameter space could be excluded at the 95 % C.L. in a high-luminosity phase of the LHC.

  • Massive charged-current coefficient functions in deep-inelastic scattering at NNLO and impact on strange-quark distributions
    JHEP 1802 (2018) 026

    by: Gao, Jun (Shanghai Jiaotong U., INPAC)

    We present details on calculation of next-to-next-to-leading order QCD corrections to massive charged-current coefficient functions in deep-inelastic scattering. Especially we focus on the application to charm-quark production in neutrino scattering on fixed target that can be measured via the dimuon final state. We construct a fast interface to the calculation so for any parton distributions the cross sections can be evaluated within milliseconds by using the pre-generated interpolation grids. We discuss agreements of various theoretical predicitons with the NuTeV and CCFR dimuon data and the impact of the results on determination of the strange-quark distributions.

  • Average CsI neutron density distribution from COHERENT data
    Phys.Rev.Lett. 120 (2018) 072501

    by: Cadeddu, M. (Cagliari U.) et al.

    Using the coherent elastic neutrino-nucleus scattering data of the COHERENT experiment, we determine for the first time the average neutron rms radius of $^{133}\text{Cs}$ and $^{127}\text{I}$. We obtain the practically model-independent value $ R_{n} = 5.5 {}^{+0.9}_{-1.1} \, \text{fm} $ using the symmetrized Fermi and Helm form factors. We also point out that the COHERENT data show a $2.3\sigma$ evidence of the nuclear structure suppression of the full coherence.

  • Higgs production at future e$^{+}$e$^{−}$ colliders in the Georgi-Machacek model
    JHEP 1802 (2018) 007

    by: Li, Bin (Nankai U.) et al.

    We study how the dominant single and double SM-like Higgs ($h$) production at future $e^+e^-$ colliders is modified in the Georgi-Machacek (GM) model. On imposing theoretical, indirect and direct constraints, significant deviations of $h$-couplings from their SM values are still possible; for instance, the Higgs-gauge coupling coupling can be corrected by a factor $\kappa_{hVV}\in[0.93,1.15]$ in the allowed parameter space. For the Higgs-strahlung $e^+e^-\to hZ$ and vector boson fusion processes $e^+e^-\to h\nu\bar{\nu},~he^+e^-$, the cross section could increase by $32\%$ or decrease by $13\%$. In the case of associated production with a top quark pair $e^+e^-\to ht\bar{t}$, the cross section can be enhanced up to several times when the custodial triplet scalar $H_3^0$ is resonantly produced. In the meanwhile, the double Higgs production $e^+e^-\to hhZ~(hh\nu\bar{\nu})$ can be maximally enhanced by one order of magnitude at the resonant $H_{1,3}^0$ production. We also include exclusion limits expected from future LHC runs at higher energy and luminosity and discuss their further constraints on the relevant model parameters. We find that the GM model can result in likely measurable deviations of Higgs production from the SM at future $e^+e^-$ colliders.

  • Fast Neutrino Flavor Conversion as Oscillations in a Quartic Potential
    Phys.Rev. D97 (2018) 023017

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

    Neutrinos in dense environments undergo collective pair conversions νeν¯e↔νxν¯x, where x is a nonelectron 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 μ=2GFnν, which can far exceed the usual neutrino oscillation frequency ω=Δm2/(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 μ but seeded by slower subleading effects.

  • Non-standard neutrino self-interactions in a supernova and fast flavor conversions
    Phys.Rev. D97 (2018) 043011

    by: Dighe, Amol (Tata Inst.) et al.

    We study the effects of non-standard self-interactions (NSSI) of neutrinos streaming out of a core-collapse supernova. We show that with NSSI, the standard linear stability analysis gives rise to linearly as well as exponentially growing solutions. For a two-box spectrum, we demonstrate analytically that flavor-preserving NSSI lead to a suppression of bipolar collective oscillations. In the intersecting four-beam model, we show that flavor-violating NSSI can lead to fast oscillations even when the angle between the neutrino and antineutrino beams is obtuse, which is forbidden in the Standard Model. This leads to the new possibility of fast oscillations in a two-beam system with opposing neutrino-antineutrino fluxes, even in the absence of any spatial inhomogeneities. Finally, we solve the full non-linear equations of motion in the four-beam model numerically, and explore the interplay of fast and slow flavor conversions in the long-time behavior, in the presence of NSSI.

  • Same Sign versus Opposite Sign Dileptons as a Probe of Low Scale Seesaw Mechanisms
    Phys.Rev. D97 (2018) 015018

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

    We calculate the ratio $R_{\ell\ell}$ of same sign (SS) to opposite sign (OS) dileptons in type I and generalized inverse seesaw models and show that it can be anywhere between 0 and 1 depending on the detailed texture of the right-handed neutrino mass matrix. Measurement of $R_{\ell\ell}$ in hadron colliders can therefore provide a way to probe the nature of seesaw mechanism and also to distinguish between the two types of seesaw mechanisms. We work within the framework of left-right symmetric model as an example. We emphasize that coherence of the final states in the $W_R$ decay is crucial for this discussion and it requires the right-handed neutrinos to be highly degenerate. We isolate the range of parameters in the model where this effect is observable at the LHC and future colliders.

  • Strange mechanics of the neutrino flavor pendulum
    Phys.Rev. D97 (2018) 023020

    by: Johns, Lucas (UC, San Diego) et al.

    We identify in the flavor transformation of astrophysical neutrinos a new class of phenomena, a common outcome of which is the suppression of flavor conversion. Appealing to the equivalence between a bipolar neutrino system and a gyroscopic pendulum, we find that these phenomena have rather striking interpretations in the mechanical picture: in one instance, the gyroscopic pendulum initially precesses in one direction, then comes to a halt and begins to precess in the opposite direction—a counterintuitive behavior that we analogize to the motion of a toy known as a rattleback. We analyze these behaviors in the early Universe, wherein a chance connection to sterile neutrino dark matter emerges, and we briefly suggest how they might manifest in compact-object environments.

  • Probing sterile neutrinos in the framework of inverse seesaw mechanism through leptoquark productions
    Phys.Rev. D97 (2018) 015024

    by: Das, Debottam (Bhubaneswar, Inst. Phys.) et al.

    We consider an extension of the standard model (SM) augmented by two neutral singlet fermions per generation and a leptoquark. In order to generate the light neutrino masses and mixing, we incorporate inverse seesaw mechanism. The right-handed neutrino production in this model is significantly larger than the conventional inverse seesaw scenario. We analyze the different collider signatures of this model and find that the final states associated with three or more leptons, multijet and at least one b-tagged and (or) τ-tagged jet can probe larger RH neutrino mass scale. We have also proposed a same-sign dilepton signal region associated with multiple jets and missing energy that can be used to distinguish the present scenario from the usual inverse seesaw extended SM.

  • From high-scale leptogenesis to low-scale one-loop neutrino mass generation
    Nucl.Phys. B927 (2018) 184-195

    by: Zhou, Hang (Shanghai Jiaotong U.) et al.

    We show that a high-scale leptogenesis can be consistent with a low-scale one-loop neutrino mass generation. Our models are based on the SU(3)_c\times SU(2)_L\times U(1)_Y\times U(1)_{B-L} gauge groups. Except a complex singlet scalar for the U(1)_{B-L} symmetry breaking, the other new scalars and fermions (one scalar doublet, two or more real scalar singlets/triplets and three right-handed neutrinos) are odd under an unbroken Z_2 discrete symmetry. The real scalar decays can produce an asymmetry stored in the new scalar doublet which subsequently decays into the standard model lepton doublets and the right-handed neutrinos. The lepton asymmetry in the standard model leptons then can be partially converted to a baryon asymmetry by the sphaleron processes. By integrating out the heavy scalar singlets/triplets, we can realize an effective theory to radiatively generate the small neutrino masses at the TeV scale. Furthermore, the lightest right-handed neutrino can serve as a dark matter candidate.

  • Expanding the Reach of Heavy Neutrino Searches at the LHC
    Phys.Lett. B778 (2018) 94-100

    by: Flórez, Andrés (Andes U., Bogota) et al.

    The observation of neutrino oscillations establishes that neutrinos have non-zero mass and provides one of the more compelling arguments for physics beyond the standard model (SM) of particle physics. We present a feasibility study to search for hypothetical Majorana neutrinos ( N ) with TeV scale masses, predicted by extensions of the SM to explain the small but non-zero SM neutrino mass, using vector boson fusion (VBF) processes at the 13 TeV LHC. In the context of the minimal Type-I seesaw mechanism (mTISM), the VBF production cross-section of a lepton ( ℓ ) and associated heavy Majorana neutrino ( Nℓ ) surpasses that of the Drell–Yan process at approximately mNℓ=1.4TeV . We consider second and third-generation heavy neutrino ( Nμ or Nτ , where ℓ = muon ( μ ) or tau ( τ ) leptons) production through VBF processes, with subsequent Nμ and Nτ decays to a lepton and two jets, as benchmark cases to show the effectiveness of the VBF topology for Nℓ searches at the 13 TeV LHC. The requirement of a dilepton pair combined with four jets, two of which are identified as VBF jets with large separation in pseudorapidity and a TeV scale dijet mass, is effective at reducing the SM background. These criteria may provide expected exclusion bounds, at 95% confidence level, of mNℓ<1.7 (2.4) TeV, assuming 100 (1000) fb−1 of 13 TeV data from the LHC and mixing |VℓNℓ|2=1 . The use of the VBF topology to search for mNℓ increases the discovery reach at the LHC, with expected significances greater than 5 σ (3 σ ) for Nℓ masses up to 1.7 (2.05) TeV using 1000fb−1 of 13 TeV data from the LHC.

  • Sterile neutrinos and B–L symmetry
    Phys.Lett. B777 (2018) 381-387

    by: Fileviez Perez, Pavel (Case Western Reserve U.) et al.

    We revisit the relation between the neutrino masses and the spontaneous breaking of the B-L gauge symmetry. We discuss the main scenarios for Dirac and Majorana neutrinos and point out two simple mechanisms for neutrino masses. In this context the neutrino masses can be generated either at tree level or at quantum level and one predicts the existence of very light sterile neutrinos with masses below the eV scale. The predictions for lepton number violating processes such as mu to e and mu to e gamma are discussed in detail. The impact from the cosmological constraints on the effective number of relativistic degree of freedom is investigated.

  • The Dark Sequential Z' Portal: Collider and Direct Detection Experiments
    Phys.Rev. D97 (2018) 043009

    by: Arcadi, Giorgio (Heidelberg, Max Planck Inst.) et al.

    We revisit the status of a Majorana fermion as a dark matter candidate when a sequential Z' gauge boson dictates the dark matter phenomenology. Direct dark matter detection signatures rise from dark matter-nucleus scatterings at bubble chamber and liquid xenon detectors, and from the flux of neutrinos from the Sun measured by the IceCube experiment, which is governed by the spin-dependent dark matter-nucleus scattering. On the collider side, LHC searches for dilepton and mono-jet + missing energy signals play an important role. The relic density and perturbativity requirements are also addressed. By exploiting the dark matter complementarity we outline the region of parameter space where one can successfully have a Majorana dark matter particle in light of current and planned experimental sensitivities.

  • Phenomenology of the gauge symmetry for right-handed fermions
    Eur.Phys.J. C78 (2018) 103

    by: Chao, Wei (Beijing Normal U.)

    In this paper we investigate the phenomenology of the U(1) gauge symmetry for right-handed fermions, where three right-handed neutrinos are introduced for anomalies cancellation. Constraints on the new gauge boson $Z_{\mathbf{R}}$ arising from $Z-Z^\prime$ mixing as well as the upper bound of $Z^\prime$ production cross section in di-lepton channel at the LHC are presented. We further study the neutrino mass generation and the phenomenology of $Z_{\mathbf{R}}$-portal dark matter in this model. The lightest right-handed neutrino can be the cold dark matter candidate stabilized by a $Z_2$ flavor symmetry. Our results show that active neutrino masses can be generated via the modified type-II seesaw mechanism; right-handed neutrino dark matter is available only for its mass at near the resonant regime of the SM Higgs and/or the new bosons; constraint from the dilepton search at the LHC is stronger than that from the $Z-Z^\prime$ mixing only for $g_\mathbf{R}<0.121$, where $g_\mathbf{R}$ is the new gauge coupling.

  • Multi-angle calculation of the matter-neutrino resonance near an accretion disk
    JCAP 1802 (2018) 010

    by: Shalgar, Shashank (Los Alamos Natl. Lab., Theor. Div.)

    We perform a numerical study of the matter-neutrino resonance in a multi-angle calculation in the vicinity of an accretion disk. We assume thermally distributed neutrino and anti-neutrino fields emitted by two-dimensional disk that is homogeneous and isotropic; the electrons are assumed to be at constant density. We compare the the result of this computation to that obtained using single-angle approximation. We investigate the robustness of matter-neutrino resonance in environment surrounding accretion disks by progressively relaxing the single angle approximation. We find that the multi-angle results in the present simplified model do not support a robust resonance mechanism as suggested by the single angle treatment. We also discuss the context under which matter-neutrino resonance may be important in future studies.

  • Cobimaximal neutrino mixing from $S_3 \times Z_2$
    Phys.Lett. B777 (2018) 332-334

    by: Ma, Ernest (Hong Kong U. Sci. Tech.)

    It has recently been shown that the phenomenologically successful pattern of cobimaximal neutrino mixing ( θ13≠0 , θ23=π/4 , and δCP=±π/2 ) may be achieved in the context of the non-Abelian discrete symmetry A4 . In this paper, the same goal is achieved with S3×Z2 . The residual lepton Z3 triality in the case of A4 is replaced here by Z2×Z2 . The associated phenomenology of the scalar sector is discussed.

  • Minimal realization of right-handed gauge symmetry
    Phys.Rev. D97 (2018) 015015

    by: Nomura, Takaaki (Korea Inst. Advanced Study, Seoul) et al.

    We propose a minimally extended gauge symmetry model with U(1)R, where only the right-handed fermions have nonzero charges in the fermion sector. To achieve both anomaly cancellations and minimality, three right-handed neutrinos are naturally required, and the standard model Higgs has to have nonzero charge under this symmetry. Then we find that its breaking scale(Λ) is restricted by precise measurement of neutral gauge boson in the standard model; therefore, O(10) TeV≲Λ. We also discuss its testability of the new gauge boson and discrimination of U(1)R model from U(1)B-L one at collider physics such as LHC and ILC.

  • Interpreting the $R_{K^{(*)}}$ anomaly in the colored Zee–Babu model
    Nucl.Phys. B928 (2018) 435-447

    by: Guo, Shu-Yuan (Nankai U.) et al.

    We consider the feasibility of interpreting the $R_{K^{(*)}}$ anomaly in the colored Zee-Babu model. The model generates neutrino masses at two loops with the help of a scalar leptoquark $S\sim(3,3,-\frac{1}{3})$ and a scalar diquark $\omega\sim(6,1,-\frac{2}{3})$, and contributes to the transition $b\to s\ell\ell$ via the exchange of a leptoquark $S$ at tree level. Under constraints from lepton flavor violating (LFV) and flavor changing neutral current (FCNC) processes, and direct collider searches for heavy particles, we acquire certain parameter space that can accommodate the $R_{K^{(*)}}$ anomaly for both normal (NH) and inverted (IH) hierarchies of neutrino masses. We further examine the LFV decays of the $B$ meson, and find its strong correlation with the neutrino mass hierarchy, i.e., $\text{Br}(B^+ \to K^+ \mu^\pm\tau^\mp)\gtrsim\text{Br}(B^+ \to K^+ \mu^\pm e^\mp)\approx\text{Br}(B^+ \to K^+ \tau^\pm e^\mp)$ for NH, while $\text{Br}(B^+ \to K^+ \mu^\pm \tau^\mp)\ll\text{Br}(B^+ \to K^+ \mu^\pm e^\mp)\approx\text{Br}(B^+ \to K^+ \tau^\pm e^\mp)$ for IH. Among these decays, only $B^+ \to K^+ \mu^\pm e^\mp$ in the case of NH is promising at the LHCb RUN II, while for IH all LFV decays are hard to detect in the near future.

  • Stimulated transitions in resonant atom Majorana mixing
    JHEP 1802 (2018) 017

    by: Bernabeu, Jose (Valencia U.) et al.

    Massive neutrinos demand to ask whether they are Dirac or Majorana particles. Majorana neutrinos are an irrefutable proof of physics beyond the Standard Model. Neutrinoless double electron capture is not a process but a virtual $\Delta L = 2$ mixing between a parent $^AZ$ atom and a daughter $^A(Z-2)$ excited atom with two electron holes. As a mixing between two neutral atoms and the observable signal in terms of emitted two-hole X-rays, the strategy, experimental signature and background are different from neutrinoless double beta decay. The mixing is resonantly enhanced for almost degeneracy and, under these conditions, there is no irreducible background from the standard two-neutrino channel. We reconstruct the natural time history of a nominally stable parent atom since its production either by nature or in the laboratory. After the time periods of atom oscillations and the decay of the short-lived daughter atom, at observable times the relevant "stationary" states are the mixed metastable long-lived state and the non-orthogonal short-lived excited state, as well as the ground state of the daughter atom. We find that they have a natural population inversion which is most appropriate for exploiting the bosonic nature of the observed atomic transitions radiation. Among different observables of the atom Majorana mixing, we include the enhanced rate of stimulated X-ray emission from the long-lived metastable state by a high-intensity X-ray beam: a gain factor of 100 can be envisaged at current XFEL facilities. On the other hand, the historical population of the daughter atom ground state can be probed by exciting it with a current pulsed optical laser, showing the characteristic absorption lines: the whole population can be excited in a shorter time than typical pulse duration.

  • Toward a unified interpretation of quark and lepton mixing from flavor and CP symmetries
    JHEP 1802 (2018) 038

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

    We discussed the scenario that a discrete flavor group combined with CP symmetry is broken to $Z_2\times CP$ in both neutrino and charged lepton sectors. All lepton mixing angles and CP violation phases are predicted to depend on two free parameters $\theta_{l}$ and $\theta_{\nu}$ varying in the range of $[0, \pi)$. As an example, we comprehensively study the lepton mixing patterns which can be derived from the flavor group $\Delta(6n^2)$ and CP symmetry. Three kinds of phenomenologically viable lepton mixing matrices are obtained up to row and column permutations. We further extend this approach to the quark sector. The precisely measured quark mixing angles and CP invariant can be accommodated for certain values of the free parameters $\theta_{u}$ and $\theta_{d}$. A simultaneous description of quark and lepton flavor mixing structures can be achieved from a common flavor group $\Delta(6n^2)$ and CP, and accordingly the smallest value of the group index $n$ is $n=7$.

  • Fuzzy dark matter and nonstandard neutrino interactions
    Phys.Rev. D97 (2018) 043001

    by: Brdar, Vedran (Mainz U.) et al.

    We discuss novel ways in which neutrino oscillation experiments can probe dark matter. In particular, we focus on interactions between neutrinos and ultra-light ("fuzzy") dark matter particles with masses of order $10^{-22}$ eV. It has been shown previously that such dark matter candidates are phenomenologically successful and might help ameliorate the tension between predicted and observed small scale structures in the Universe. We argue that coherent forward scattering of neutrinos on fuzzy dark matter particles can significantly alter neutrino oscillation probabilities. These effects could be observable in current and future experiments. We set new limits on fuzzy dark matter interacting with neutrinos using T2K and solar neutrino data, and we estimate the sensitivity of reactor neutrino experiments and of future long-baseline accelerator experiments. These results are based on detailed simulations in GLoBES. We allow the dark matter particle to be either a scalar or a vector boson. In the latter case, we find potentially interesting connections to models addressing various $B$ physics anomalies.

  • Dark Energy from pNGB Mediated Dirac Neutrino Condensate
    Nucl.Phys. B928 (2018) 258-267

    by: Dey, Ujjal Kumar (Indian Inst. Tech., Kharagpur) et al.

    We consider an extension of the Standard Model that provide an unified description of eV scale neutrino mass and dark energy. An explicit model is presented by augmenting the Standard Model with an $SU(2)_L$ doublet scalar, a singlet scalar and a right handed neutrino where all of them are assumed to be charged under a global $U(1)_X$ symmetry. A light pseudo-Nambu-Goldstone Boson, associated with the spontaneously broken $U(1)_{X}$ symmetry, acts as a mediator of an attractive force leading to a Dirac neutrino condensate, with large correlation length, and a non-zero gap in the right range providing a cosmologically feasible dark energy scenario. The neutrino mass is generated through the usual Dirac seesaw mechanism. Parameter space, reproducing viable dark energy scenario while having neutrino mass in the right ballpark, is presented.

  • A study of invisible neutrino decay at DUNE and its effects on $\theta_{23}$ measurement
    JHEP 1802 (2018) 055

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

    We study the consequences of invisible decay of neutrinos in the context of the DUNE experiment. We assume that the third mass eigenstate is unstable and decays to a light sterile neutrino and a scalar or a pseudo-scalar. We consider DUNE running in 5 years neutrino and 5 years antineutrino mode and a detector volume of 40 kt. We obtain the expected sensitivity on the rest-frame life-time τ$_{3}$ normalized to the mass m$_{3}$ as τ$_{3}$/m$_{3}$ > 4.50 × 10$^{−11}$ s/eV at 90% C.L. for a normal hierarchical mass spectrum. We also find that DUNE can discover neutrino decay for τ$_{3}$/m$_{3}$ > 4.27 × 10$^{−11}$ s/eV at 90% C.L. In addition, for an unstable ν$_{3}$ with an illustrative value of τ$_{3}$/m$_{3}$ = 1.2 × 10$^{−11}$ s/eV, the no decay case could get disfavoured at the 3σ C.L. At 90% C.L. the expected precision range for this true value is obtained as 1.71 × 10$^{−11}$ > τ$_{3}$/m$_{3}$ > 9.29 × 10$^{−12}$ in units of s/eV. We also study the correlation between a non-zero τ$_{3}$/m$_{3}$ and standard oscillation parameters and find an interesting correlation in the appearance and disappearance channels with the mixing angle θ$_{23}$. This alters the octant sensitivity of DUNE, favorably (unfavorably) for true θ$_{23}$ in the lower (higher) octant. The effect of a decaying neutrino does not alter the hierarchy or CP violation discovery sensitivity of DUNE in a discernible way.

  • Lepton CP violation in a $\nu$2HDM with flavor
    Phys.Rev. D97 (2018) 035003

    by: Barradas-Guevara, E. (Puebla U., Mexico) et al.

    In this work we propose an extension to the Standard Model in which we consider a type-III two-Higgs-doublet model (2HDM) plus massive neutrinos and the horizontal flavor symmetry S3 (ν2HDM⊗S3). In the above framework and with the explicit breaking of flavor symmetry S3, the Yukawa matrices in the flavor-adapted basis are represented by means of a matrix with two texture zeros. Also, the active neutrinos are considered as Majorana particles and their masses are generated through the type-I seesaw mechanism. The unitary matrices that diagonalize the mass matrices, as well as the flavor-mixing matrices, are expressed in terms of fermion mass ratios. Consequently, in the mass basis the entries of the Yukawa matrices naturally acquire the form of the so-called Cheng-Sher ansatz. For the leptonic sector of ν2HDM⊗S3, we compare, through a χ2 likelihood test, the theoretical expressions of the flavor-mixing angles with the masses and flavor-mixing leptons current experimental data. The results obtained in this χ2 analysis are in very good agreement with the current experimental data. We also obtain allowed value ranges for the “Dirac-like” phase factor, as well as for the two Majorana phase factors. Furthermore, we study the phenomenological implications of these numerical values of the CP-violation phases on the neutrinoless double-beta decay, and for long baseline neutrino oscillation experiments such as T2K, NOνA, and DUNE.

  • Electron Electric Dipole Moment in Mirror Fermion Model with Electroweak Scale Non-sterile Right-handed Neutrinos
    Nucl.Phys. B928 (2018) 21-37

    by: Chang, Chia-Feng (Taiwan, Natl. Taiwan U.) et al.

    The electric dipole moment of the electron is studied in detail in an extended mirror fermion model with the following unique features of (a) right-handed neutrinos are non-sterile and have masses at the electroweak scale, and (b) a horizontal symmetry of the tetrahedral group is used in the lepton and scalar sectors. We study the constraint on the parameter space of the model imposed by the latest ACME experimental limit on electron electric dipole moment. Other low energy experimental observables such as the anomalous magnetic dipole moment of the muon, charged lepton flavor violating processes like muon decays into electron plus photon and muon-to-electron conversion in titanium, gold and lead are also considered in our analysis for comparison. In addition to the well-known CP violating Dirac and Majorana phases in the neutrino mixing matrix, the dependence of additional phases of the new Yukawa couplings in the model is studied in detail for all these low energy observables.

  • Neutrinoless double beta decay in left-right symmetric models with a universal seesaw mechanism
    Phys.Rev. D97 (2018) 035005

    by: Deppisch, Frank F. (U. Coll. London) et al.

    We discuss a class of left-right symmetric theories with a universal seesaw mechanism for fermion masses and mixing and the implications for neutrinoless double beta (0νββ) decay where neutrino masses are governed by natural type-II seesaw dominance. The scalar sector consists of left- and right-handed Higgs doublets and triplets, while the conventional Higgs bidoublet is absent in this scenario. We use the Higgs doublets to implement the left-right and the electroweak symmetry breaking. On the other hand, the Higgs triplets with induced vacuum expectation values can give Majorana masses to light and heavy neutrinos and mediate 0νββ decay. In the absence of the Dirac mass terms for the neutrinos, this framework can naturally realize type-II seesaw dominance even if the right-handed neutrinos have masses of a few TeV. We study the implications of this framework in the context of 0νββ decay.

  • On the non-detection of Glashow resonance in IceCube
    JHEAp 18 (2018) 1-4

    by: Sahu, Sarira (Mexico U., ICN) et al.

    Electron anti-neutrinos at the Glashow resonance (GR, at $E_{\bar \nu_e} \sim 6.3$ PeV) have an enhanced probability to be detected. With three neutrinos detected by IceCube in the (1-2) PeV energy range at present, one would expect that about 1 GR $\bar\nu_e$ should have been detected. The high-energy $\sim 8.7$ PeV muon neutrino detected by IceCube may not be a GR event. If so, the expected detection number of the GR $\bar\nu_e$ would be $\sim 90$, then one would have a "missing Glashow-resonance problem". This would suggest (1) that $p\gamma$ interaction rather than $pp$ interaction is the dominant channel to produce the observed IceCube high-energy neutrinos; (2) that multi-pion $p\gamma$ interactions are suppressed; and (3) that the magnetic field and photon energy density in the $p\gamma$ emission region is such that significant $\mu^+$ cooling occurs before decaying, yet $\pi^+$'s essentially do not cool before decaying.

  • Lepton flavor violation and scalar dark matter in a radiative model of neutrino masses
    Eur.Phys.J. C78 (2018) 88

    by: Esch, Sonja (Munster U., ITP) et al.

    We consider a simple extension of the Standard Model that can account for the dark matter and explain the existence of neutrino masses. The model includes a vector-like doublet of SU(2), a singlet fermion, and two scalar singlets, all of them odd under a new Z$_2$ symmetry. Neutrino masses are generated radiatively by one-loop processes involving the new fields, while the dark matter candidate is the lightest neutral particle among them. We focus specifically on the case where the dark matter particle is one of the scalars and its relic density is determined by its Yukawa interactions. The phenomenology of this setup, including neutrino masses, dark matter and lepton flavor violation, is analyzed in some detail. We find that the dark matter mass must be below $500$ GeV to satisfy the relic density constraint. Lepton flavor violating processes are shown to provide the most promising way to test this scenario. Future $\mu\to 3e$ and $\mu$-$e$ conversion experiments, in particular, have the potential to probe the entire viable parameter space of this model.

  • An $S_4$ model inspired from self-complementary neutrino mixing
    J.Phys. G45 (2018) 035004

    by: Zhang, Xinyi (Shanghai Jiaotong U., INPAC)

    We build an $S_4$ model for neutrino masses and mixings based on the self-complementary (SC) neutrino mixing pattern. The SC mixing is constructed from the self-complementarity relation plus $\delta_{\rm CP}=-\frac{\pi}{2}$. We elaborately construct the model at a percent level of accuracy to reproduce the structure given by the SC mixing. After performing a numerical study on the model's parameter space, we find that in the case of normal ordering, the model can give predictions on the observables that are compatible with their $3\sigma$ ranges, and give predictions for the not-yet observed quantities like the lightest neutrino mass $m_1\in [0.003,0.010]$ eV and the Dirac CP violating phase $\delta_{\rm CP}\in[256.72^\circ,283.33^\circ]$.

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