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  • Radiative Neutrino Mass Generation: Models, Flavour and the LHC

    by: Volkas, Raymond R. (ARC, CoEPP, Melbourne)

    Radiative neutrino mass models and the seesaw models are viewed from the unifying framework of standard model effective operators that explicitly violate lepton number by two units (ΔL = 2). After some comments on naturalness and leptogenesis in the minimal type 1 seesaw model, a full list of minimal renormalisable models that produce mass dimension-7, ΔL = 2 operators at low energies is presented. By way of example, phenomenological bounds from Run 1 LHC and lepton flavour violation data are then placed on one of these models. A possible connection between radiative neutrino mass models and the current flavour anomalies in b → c and b → s transitions is then described.

  • Fermions Masses and Texture Zero

    by: Bhatti, A.Aziz (Punjab U., CHEP)

    The Standard model of particle physics is a very successful theory of strong weak and electromagnetic interactions. This theory is perturbative at sufficiently high energies and renormalizable, it describes these interactions at quantum level. However it has a number of limitations, one being the fact that it has 28 free parameters assuming massive neutrinos. Within the Standard model these parameters can not be explained, however they can be accommodated in the standard theory. Particularly the masses of the fermions are not predicted by the theory. The existence of the neutrino masses can be regarded as the first glimpse of the physics beyond the standard model. we have described the quark and lepton masses and mixings in context of four zero texture (FZT). In the four zero texture case the fermion masses and mixing can be related. We have made some predictions using tribimaximal mixing, the near tribimaximal (TBM) mixing. Our results show that under the TBM the neutrinos have normal, but weak hierarchy. Under near tribimaximal mixing, we find that the neutrino masses in general increase, if the value of solar angle increases from its TBM value and vice versa. It appears that the neutrinos become more and more degenerate for solar angle values higher than TBM value and hierarchical for lower values of solar angle.

  • Implications of Higgs’ Universality for Physics Beyond the Standard Model

    by: Goldman, T. (New Mexico U.) et al.

    We emulate Cabibbo by assuming a kind of universality for fermion mass terms in the Standard Model. We show that this is consistent with all current data and with the concept that deviations from what we term Higgs’ universality are due to corrections from currently unknown physics of nonetheless conventional form. The application to quarks is straightforward, while the application to leptons makes use of the recognition that Dark Matter can provide the “sterile” neutrinos needed for the seesaw mechanism. Requiring agreement with neutrino oscillation results leads to the prediction that the mass eigenstates of the sterile neutrinos are separated by quadratically larger ratios than for the charged fermions. Using consistency with the global fit to LSND-like, short-baseline oscillations to determine the scale of the lowest mass sterile neutrino strongly suggests that the recently observed astrophysical 3.55 keV γ-ray line is also consistent with the mass expected for the second most massive sterile neutrino in our analysis.

  • Dark Matter and Baryogenesis from non-Abelian Gauged Lepton Number

    by: Fornal, Bartosz (UC, San Diego)

    A simple model is constructed based on the gauge symmetry SU(3)c×SU(2)L×U(1)Y × SU(2)l, with only the leptons transforming nontrivially under SU(2)l. The extended symmetry is broken down to the Standard Model gauge group at TeV-scale energies. We show that this model provides a mechanism for baryogenesis via leptogenesis in which the lepton number asymmetry is generated by SU(2)l instantons. The theory also contains a dark matter candidate — the SU(2)l partner of the right-handed neutrino.

  • Neutrinoless Double-Beta Decays: New Insights

    by: Xing, Z.Z. (Liaoning Normal U.) et al.

    We give some new insights into the effective Majorana neutrino mass 〈m〉ee responsible for the neutrinoless double-beta (0v2β) decays. We put forward a three-dimensional way of plotting |〈m〉ee| against the lightest neutrino mass and the Majorana phases, which can provide more information as compared with the two-dimensional one. With the help of such graphs we discover a novel threshold of |〈m〉ee| in terms of the neutrino masses and flavor mixing angles: |〈m〉ee|* = m3 sin2 θ13 in connection with and ρ = π, which can be used to signify observability of the future 0v2β-decay experiments. Fortunately, the possibility of |〈m〉ee| < |〈m〉ee|* turns out to be very small, promising a hopeful prospect for the 0v2β-decay searches.

  • Neutrinos and Cosmological Matter–antimatter Asymmetry: A Minimal Seesaw with Frampton–Glashow–Yanagida Ansatz

    by: Zhang, Jue (Beijing, Inst. High Energy Phys.) et al.

    In light of the latest neutrino data, we revisit a minimal seesaw model with the Frampton–Glashow–Yanagida ansatz. Renormalization-group running effects on neutrino masses and flavor mixing parameters are discussed and found to essentially have no impact on testing such a minimal scenario in low-energy neutrino experiments. However, since renormalization-group running can modify neutrino mixing parameters at high energies, it does affect the leptogenesis mechanism, which is responsible for the observed matter–antimatter asymmetry in our Universe. Furthermore, to ease the conflict between the naturalness argument and the successful leptogenesis, a special regime for resonant leptogenesis is also emphasized.

  • Nonzero θ 13 and CP violation from cobimaximal neutrino mixing matrix
    J.Phys.Conf.Ser. 909 (2017) 012024

    by: Damanik, Asan (Gama Research Ctr., Yogyakarta)

    The nonzero mixing angle θ 13 have been reported and confirmed by many collaborations. If the mixing angle θ 13 is nonzero, then the possiblity of the CP violation existence on neutrino sector become an attractive research subject both from experimental and theoretical sides. We evaluate the power predictions of cobimaximal neutrino mixing matrix on mixing angle θ 13 and CP violation for neutrino sector by determining the Jarlskog invariant as a measure of CP violation.

  • Radiative Dirac neutrino mass, DAMPE dark matter and leptogenesis

    by: Gu, Pei-Hong
    We explain the electron-positron excess reported by the DAMPE collaboration recently in a radiative Dirac seesaw model where a dark $U(1)_X$ gauge symmetry can (i) forbid the tree-level Yukawa couplings of three right-handed neutrinos to the standard model lepton and Higgs doublets, (ii) predict the existence of three dark fermions for the gauge anomaly cancellation, (iii) mediate a testable scattering of the lightest dark fermion off the nucleons. Our model can also accommodate a successful leptogenesis to generate the cosmic baryon asymmetry.

  • Spotlighting the sensitivities of T2HK,T2HKK and DUNE

    by: Chakraborty, Kaustav
    Neutrino oscillation physics has entered the precision era and the potential forthcoming experiments Hyper-Kamiokande and Deep Under-ground Neutrino Experiment (DUNE) are expected to lead this endeavor. In this paper we perform a comprehensive study of the octant, mass hierarchy and CP discovery sensitivities of DUNE, T2HK & T2HKK in their individual capacity and investigate the synergies of the aforementioned experiments with the on going T2K and NO$\nu$A experiments. We present a comparative account of the probabilities at the three baselines and explore in detail the physics issues which can cause the discrepancies in the sensitivities among the different experiments. We also find out the optimal exposure required by these experiments for achieving $5\sigma$ hierarchy and octant sensitivity and to discover CP violation at $3\sigma$ for 60\% values of $\delta_{CP}$. In addition we vary the neutrino-antineutrino runtime ratios for T2HK & T2HKK and check if the sensitivities are affected significantly due to this.

  • Measurement of the Energy-Dependent Neutrino-Nucleon Cross Section Above 10 TeV Using IceCube Showers

    by: Bustamante, Mauricio
    Neutrinos are key to probing the deep structure of matter and the high-energy Universe. Yet, until recently, their interactions had only been measured at laboratory energies up to about 350 GeV. An opportunity to measure their interactions at higher energies opened up with the detection of high-energy neutrinos in IceCube, partially of astrophysical origin. Scattering off matter inside the Earth affects the distribution of their arrival directions --- from this, we extract the neutrino-nucleon cross section at energies from 18 TeV to 2 PeV, in four energy bins, in spite of uncertainties in the neutrino flux. Using six years of public IceCube High-Energy Starting Events, we explicitly show for the first time that the energy dependence of the cross section above 18 TeV agrees with the predicted softer-than-linear dependence, and reaffirm the absence of new physics that would make the cross section rise sharply, up to a center-of-mass energy of ~1 TeV.

  • Discrete Flavour Symmetries, Neutrino Mixing and Leptonic CP Violation

    by: Petcov, S.T.
    The current status of our knowledge of the 3-neutrino mixing parameters and of the CP violation in the lepton sector is summarised. The discrete symmetry approach to understanding the observed pattern of neutrino mixing and the related predictions for neutrino mixing angles and leptonic Dirac CP violation are reviewed.

  • Dirac neutrinos, dark matter stability and flavour predictions from Lepton Quarticity

    by: Centelles Chuliá, Salvador
    We propose to relate dark matter stability to the possible Dirac nature of neutrinos. The idea is illustrated in a simple scheme where small Dirac neutrino masses arise from a type-I seesaw mechanism as a result of a $Z_4$ discrete lepton number symmetry. The latter implies the existence of a viable WIMP dark matter candidate, whose stability arises from the same symmetry which ensures the Diracness of neutrinos. The symmetry groups $\Delta_{27}$ and $A_4$ are then used to extract a rich variety of flavour predictions.

  • A model explaining neutrino masses and the DAMPE cosmic ray electron excess

    by: Fan, Yi-Zhong
    We propose a flavored $U(1)_{e\mu}$ neutrino mass and dark matter (DM) model to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only the first two lepton generations of the Standard Model are charged under the new $U(1)_{e\mu}$ gauge symmetry. A vector-like fermion $\psi$, which is our DM candidate, annihilates into $e^{\pm}$ and $\mu^{\pm}$ via the new gauge boson $Z'$ exchange and accounts for the DAMPE excess. We have found that the data favors a $\psi$ mass around 1.5~TeV and a $Z'$ mass around 2.6~TeV, which can potentially be probed by the next generation lepton colliders and DM direct detection experiments.

  • The λ Mechanism of the 0νββ-Decay Phys. 5 (2017) 57

    by: Šimkovic, Fedor (Comenius U.) et al.

    The λ mechanism (WL − WR exchange) of the neutrinoless double beta decay (0νββ-decay), which has origin in left-right symmetric model with right-handed gauge boson at TeV scale, is investigated. The revisited formalism of the 0νββ-decay, which includes higher order terms of nucleon current, is exploited. The corresponding nuclear matrix elements are calculated within quasiparticle random phase approximation with partial restoration of the isospin symmetry for nuclei of experimental interest. A possibility to distinguish between the conventional light neutrino mass (WL − WL exchange) and λ mechanisms by observation of the 0νββ-decay in several nuclei is discussed. A qualitative comparison of effective lepton number violating couplings associated with these two mechanisms is performed. By making viable assumption about the seesaw type mixing of light and heavy neutrinos with the value of Dirac mass mD within the range 1 MeV < mD < 1 GeV, it is concluded that there is a dominance of the conventional light neutrino mass mechanism in the decay rate.

  • Neutrinoless Double Beta Decay and the Baryon Asymmetry of the Universe

    by: Deppisch, Frank F.
    We discuss the impact of the observation of neutrinoless double beta decay on the washout of lepton number in the early universe. Neutrinoless double beta decay can be triggered by a large number of mechanisms that can be encoded in terms of Standard Model effective operators which violate lepton number by two units. We calculate the contribution of such operators to the rate of neutrinoless double beta decay and correlate it with the washout of lepton number induced by the same operators in the early universe. We find that the observation of a non-standard contribution to neutrinoless double beta decay, i.e. not induced by the standard mass mechanism of light neutrino exchange, would correspond to an efficient washout of lepton number above the electroweak scale for many operators up to mass dimension 11. Combined with Standard Model sphaleron transitions, this would render many baryogenesis mechanisms at higher scales ineffective.

  • Why one neutrino is probably a tachyon: a review of the $3+3$ model and its well-satisfied predictions

    by: Ehrlich, Robert
    A review is given of hypothetical faster-than-light tachyons and the development of the author's $3+3$ model of the neutrino mass states, which includes one tachyonic mass state doublet. Published empirical evidence for the model is summarized, including a new interpretation of the mysterious Mont Blanc neutrino burst from SN 1987A as being due to tachyonic neutrinos having $m^2=-0.38 eV^2.$ This possibility requires an 8 MeV antineutrino line from SN 1987A, which a new dark matter model has been found to support. Furthermore, this dark matter model is supported by several data sets: $\gamma-$rays from the galactic center, and the Kamiokande-II data on the day of SN 1987A.

  • Testing a lepton quarticity flavor theory of neutrino oscillations with the DUNE experiment

    by: Srivastava, Rahul
    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.

  • Heavy Majorana neutrino pair productions at the LHC in minimal U(1) extended Standard Model

    by: Das, Arindam
    In our recent paper [1], we explored a prospect of discovering the heavy Majorana right-handed neutrinos (RHNs) at the future LHC in the context of the minimal non-exotic U(1) extended Standard Model (SM), where a pair of RHNs are created via decay of resonantly produced massive U(1) gauge boson ($Z^{\prime}$). We pointed out that this model can yield a significant enhancement of the branching ratio of the $Z^\prime$ boson to a pair of RHNs, which is crucial for discovering the RHNs under the very severe LHC Run-2 constraint from the search for the $Z^\prime$ boson with dilepton final states. In this paper, we perform a general parameter scan to evaluate the maximum production rate of the same-sign dilepton final states (smoking gun signature of Majorana RHNs production) at the LHC, while reproducing the neutrino oscillation data. We also consider the minimal non-exotic U(1) model with an alternative charge assignment. In this case, we find a further enhancement of the branching ratio of the $Z^\prime$ boson to a pair of RHNs compared to the conventional case, which opens up a possibility of discovering the RHNs even before the $Z^\prime$ boson at the future LHC experiment.

  • Dark neutrino interactions make gravitational waves blue

    by: Ghosh, Subhajit
    New interactions of neutrinos can stop these from free streaming in the early Universe even after the weak decoupling epoch. This results in the enhancement of primordial gravitational wave amplitude on small scales compared to the standard $\Lambda$CDM prediction. In this paper we calculate the effect of dark matter neutrino interactions in CMB tensor $B$-mode spectrum. We show that the effect of new neutrino interactions generates a scale or $\ell$ dependent imprint in the CMB $B$-mode power spectrum at $\ell \gtrsim 100$. In the event that primordial $B$-modes are detected by future experiments, a departure from scale invariance, with a blue spectrum, may not necessarily mean failure of simple inflationary models but instead may be a sign of non-standard interactions of relativistic particles. There is rich information hidden in the CMB $B$-mode spectrum beyond just the tensor to scalar ratio.

  • COHERENT constraints to conventional and exotic neutrino physics

    by: Kosmas, T.S.
    The process of neutral-current coherent elastic neutrino-nucleus scattering (CE$\nu$NS), consistent with the Standard Model (SM) expectation has been recently measured by the COHERENT experiment at the Spallation Neutron Source, Oak Ridge. On the basis of the observed signal and our nuclear calculations for the relevant Cs and I isotopes, the extracted constraints on both conventional and exotic neutrino physics are updated. The present study concentrates on various SM extensions involving vector and tensor non-standard interactions (NSI) as well as neutrino electromagnetic properties with emphasis on the neutrino magnetic moment and the neutrino charge-radius. Furthermore, models addressing a light sterile neutrino state and scenarios with new propagator fields such as vector $Z^\prime$ and scalar bosons are examined, and the corresponding excluded regions by the COHERENT experiment are presented.

  • A simple model to explain the observed muon sector anomalies, small neutrino masses, baryon-genesis and dark-matter

    by: Dhargyal, Lobsang
    Since its inception, no decisive departure from the predictions of Standard Model (SM) has been reported. But recently various experiments have observed few hints of possible departure from SM predictions in lepton flavor universality observables such as $R_{K^{(*)}}$, $P_{5}^{'}$, muon (g-2), $R(D^{(*)})$ etc. Many of these observable where deviation from SM in the range of (2-4)$\sigma$ were observed are related to muon ($\mu$) lepton. So these deviations may be some hint of a possible New Physics (NP) in the muon sector. In this work we extend the SM by introducing two SM singlet heavy charged leptons ($F_{e},\ F_{\mu}$) whose left handed components are charged under a new $U(1)_{F}$ gauge symmetry, one color triplet lepto-quark ($\phi_{Q}$) doublet under $SU(2)_{L}$, one inert Higgs doublet ($\phi_{l}$), three very heavy Majorana neutrinos ($N_{iR}$) and one SM singlet scalar Dark Matter (DM) particle (S), all of which are odd under a $Z_{2}$ discrete symmetry. One more scalar ($\phi$) charged only under the $U(1)_{F}$ whose VEV give masses to the $U(1)_{F}$ gauge boson as well as the heavy leptons. With these new particles, we show that the observed anomalies in the muon sector as well as small neutrino masses, baryon-genesis and DM all can be explained with taking into account all the other experimental and theoretical constrains till date.

  • Solar flares and their associated processes

    by: Boyarkin, O.M.
    The evolution of the solar neutrino flux which is described by the wave function $\Psi^T=(\nu_{eL},\nu_{XL}, \overline{\nu}_{eL}, \overline{\nu}_{XL})$ is examined. Our treatment of the problem holds for any standard model (SM) extensions possessing nonzero dipole magnetic and anapole moments. When the solar neutrino flux moves through the solar flare (SF) region in the preflare period, then it undergoes the additional (compared with the SM) resonance conversions. As a result, the weakening the electron neutrinos flux takes place. On the other hand, existence of the additional resonances lead to appearance of the $\overline{\nu}_{eL}$ and $\overline{\nu}_{XL}$ neutrinos that could be detected by the terrestrial detectors. The hypothesis of the $\nu_e$-induced $\beta$-decays is also discussed. According to it, before the large SF, decreasing the $\beta$-decay rate for some elements takes place. The possible influence of the electron antineutrino flux produced in the superflares on the regime of the hypothetical georeactor is considered.

  • Non-minimal quartic inflation in classically conformal U(1)$_X$ extended Standard Model

    by: Oda, Satsuki
    We propose quartic inflation with non-minimal gravitational coupling in the context of the classically conformal U(1)_X extension of the SM. In this model, the U(1)_X gauge symmetry is radiatively broken through the Coleman-Weinberg (CW) mechanism, by which the U(1)_X gauge boson (Z' boson) and the right-handed neutrinos (RHNs) acquire their masses. We consider their masses in the range of O(10 GeV)-O(10 TeV), which are accessible to high energy collider experiments. The radiative U(1)_X gauge symmetry breaking also generates a negative mass squared for the SM Higgs doublet, and the electroweak symmetry breaking occurs subsequently. We identify the U(1)_X Higgs field with inflaton and calculate the inflationary predictions. Due to the CW mechanism, the inflaton quartic coupling during inflation, which determines the inflationary predictions, is correlated to the U(1)_X gauge coupling. With this correlation, we investigate complementarities between the inflationary predictions and the current constraint from the Z' boson resonance search at the LHC Run-2 as well as the prospect of the search for the Z' boson and the RHNs at the future collider experiments. The radiative U(1)_X gauge symmetry breaking also generates a negative mass squared for the SM Higgs doublet, and the electroweak symmetry breaking occurs subsequently. We identify the U(1)_X Higgs field with inflaton and calculate the inflationary predictions. Due to the Coleman-Weinberg mechanism, the inflaton quartic coupling during inflation, which determines the inflationary predictions, is correlated to the U(1)_X gauge coupling. With this correlation, we investigate complementarities between the inflationary predictions and the current constraint from the Z' boson resonance search at the LHC Run-2 as well as the prospect of the search for the Z' boson and the RHNs at the future collider experiments.

  • IceCube's astrophysical neutrino energy spectrum from CPT violation

    by: Liao, Jiajun
    The 6-year dataset of high-energy starting events (HESE) at IceCube indicates a spectrum of astrophysical neutrinos much softer than expected from the Fermi shock acceleration mechanism. On the other hand, IceCube's up-going muon neutrino dataset and Fermi-LAT's gamma-ray spectrum point to an $E^{-2}$ neutrino spectrum. If the HESE data above 200 TeV are fit with the latter flux, an excess at lower energies ensues, which then suggests a multicomponent spectrum. We show that the HESE dataset can be explained by a single $E^{-2}$ power-law neutrino flux from a muon-damped $p\gamma$ source if neutrino interactions are modified by CPT violation. The low-energy excess is naturally explained by the pile up of events from superluminal neutrino decay, and there is no cutoff at high energies due to the contribution of subluminal antineutrinos. The best-fit scenario with CPT violation also predicts the observation of Glashow resonance events in the near future.

  • Quark-lepton complementarity model based predictions for $\theta_{23}^{PMNS}$ with neutrino mass hierarchy

    by: Sharma, Gazal
    After the successful investigation and confirmation of non zero $\theta_{13}^{PMNS}$ by various experiments, we are standing at a square where we still encounter a number of issues, which are to be settled. In this paper, we have extended our recent work towards a precise prediction of the $\theta_{23}^{PMNS}$ mixing angle, taking into account the neutrino mass hierarchy. We parameterize the non-trivial correlation between quark (CKM) and lepton (PMNS) mixing matrices in quark-lepton complementarity (QLC) model as $V_{c}= U_{CKM}. \psi. U_{PMNS}$, where $\psi$ is a diagonal phase matrix. Monte Carlo simulations are used to estimate the texture of $V_{c}$ and compare the results with the standard Tri-Bi-Maximal (TBM) and Bi-Maximal(BM) structures of neutrino mixing matrix. We have predicted the value of $\theta_{23}^{PMNS} $ for normal and inverted neutrino mass hierarchies. The value of $\theta_{23}^{PMNS}$ obtained for two cases are about $1.3\sigma$ away from each other, implying the better precision can give us a strong hint for the type of neutrino mass hierarchy.

  • GeV-scale hot sterile neutrino oscillations: a numerical solution

    by: Ghiglieri, J.
    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.

  • D meson production asymmetry, unfavoured fragmentation and consequences for prompt atmospheric neutrino production

    by: Maciula, Rafal
    We consider unfavoured light quark/antiquark to $D$ meson fragmentation. We discuss nonperturbative effects for small transverse momenta. The asymmetry for $D^+$ and $D^-$ production measured by the LHCb collaboration provides natural constraints on the parton (quark/antiquark) fragmentation functions. We find that already a fraction of $q/{\bar q} \to D$ fragmentation probability is sufficient to account for the measured asymmetry. We make predictions for similar asymmetry for neutral $D$ mesons. Large $D$-meson production asymmetries are found for large $x_F$ which is related to dominance of light quark/antiquark $q/\bar q \to D$ fragmentation over the standard $c \to D$ fragmentation. As a consequence, prompt atmospheric neutrino flux at high neutrino energies can be much larger than for the conventional $c \to D$ fragmentation. The latter can constitute a sizeable background for the cosmic neutrinos claimed to be observed recently by the IceCube Observatory. Large rapidity-dependent $D^+/D^-$ and $D^0/{\bar D}^0$ asymmetries are predicted for low ($\sqrt{s} =$ 20 - 100 GeV) energies. The $q/\bar q \to D$ fragmentation leads to enhanced production of $D$ mesons at low energies. At $\sqrt{s}$ = 20 GeV the enhancement factor with respect to the conventional contribution is larger than a factor of five. In the considered picture the large-$x_F$ $D$ mesons are produced dominantly via fragmentation of light quarks/antiquarks. Predictions for fixed target $p+^{4}\!\textrm{He}$ collisions relevant for a fixed target LHCb experiment are presented.

  • Neutrinoless double beta-decay and neutrino nonstandard interactions
    Phys.Part.Nucl. 48 (2017) 1023-1025
    Fiz.Elem.Chast.Atom.Yadra 48 (2017)

    by: Šimkovic, F. (Comenius U.) et al.

    The possible amplification of leptons and quarks in exotic scalar interactions in the nuclear medium violates lepton number conservation. This effect results in various neutrino masses that are measured experimentally, on the one hand, in 0νββ-decay and, on the other, in β-decay of tritium and in cosmology.

  • Cosmological bounds on neutrino degeneracy and the Dirac neutrino magnetic moment
    Phys.Part.Nucl. 48 (2017) 1021-1022

    by: Semikoz, V.B. (Troitsk, IZMIRAN)

    The amplification of a seed cosmological magnetic field (CMF) in a hot electroweak plasma of early Universe driven by neutrino degeneracy (asymmetry) is provided by a lower bound on such asymmetries that is in agreement with the known upper (BBN) bound on the electron neutrino asymmetry. Independently of a mechanism for CMF generation one predicts a stringent upper bound on the Dirac neutrino magnetic moment using the lower bound on CMF amplitude found from the Fermi satellite experiment.

  • Generalized tree-level scattering amplitude in a magnetized medium
    Phys.Part.Nucl. 48 (2017) 1000-1001
    Fiz.Elem.Chast.Atom.Yadra 48 (2017)

    by: Kuznetsov, A.V. (Yaroslavl State U.) et al.

    Tree-level two-point jf → j′f′ transitions amplitudes in a constant uniform magnetic field of an arbitrary strength and in charged fermion plasma, for different combinations of scalar, pseudoscalar, vector, and axial-vector vertices are calculated. The obtained results are applied to analysis of the neutrino photoproduction process, γe → $ev\bar v$ , taking account of a possible resonance on the virtual electron in the conditions of dense strongly magentized plasma.

  • Neutrino production of electron–positron pairs in a moderately strong magnetic field
    Phys.Part.Nucl. 48 (2017) 998-999
    Fiz.Elem.Chast.Atom.Yadra 48 (2017)

    by: Kuznetsov, A.V. (Yaroslavl State U.) et al.

    Neutrino production of electron–positron pairs via the processes $v\bar v$ → e$^{−}$ e$^{+}$ and ν → νe$^{−}$ e$^{+}$ in a moderately strong magnetic field is investigated. Under these conditions electrons and positrons can be produced in the states corresponding to excited Landau levels. The results can be used for calculating the efficiency of the electron–positron plasma production by neutrinos in the conditions of the accretion disk around a Kerr black hole.

  • Oscillation characteristics of neutrino in the model with three sterile neutrinos for analysis of the anomalies on small distances
    Phys.Part.Nucl. 48 (2017) 990-992

    by: Khruschov, V.V. (Kurchatov Inst., Moscow) et al.

    In the framework of the model with three sterile neutrinos, the transition probabilities for different flavours of neutrino are calculated and the graphical dependences are obtained, in particular, for the appearance probability of electron neutrino and antineutrino in the muon neutrino and antineutrino jets as a function of distance and other model parameters at their acceptable values and at the neutrino energy less than 50 MeV, as well as a function of a ratio of distance to the neutrino energy. The theoretical results obtained can be used for analysis of the neutrino data related to the anomalies on small distances.

  • Deviations of exact neutrino textures using radiative neutrino masses

    by: Wegman, D.
    The Weinberg operator allows for the construction of radiative Majorana neutrino masses. In this letter, it will be shown that it is possible to construct a one-loop diagram that will be the principal component of the neutrino mass matrix and that will have an exact mixing matrix with $\theta_{13} =0$. The addition of a two-loop diagram, which is naturally suppressed, allows the creation of the correct perturbations that will give a neutrino mixing matrix with entries inside experimental constrains, including the possibility of large CP Dirac phases.

  • Neutrino Mass Priors for Cosmology from Random Matrices

    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.

  • Multi-lepton signatures of additional scalar bosons beyond the Standard Model at the LHC

    by: von Buddenbrock, Stefan
    Following Refs. \cite{vonBuddenbrock:2015ema,Kumar:2016vut,vonBuddenbrock:2016rmr}, in this paper we focus on multi-lepton signatures arising from two new scalar bosons $H$ and $S$ at the Large Hadron Collider (LHC). These two new bosons are an extension to the Standard Model (SM) and interact with the SM Higgs boson, $h$. We consider two production modes for $H$, one being gluon fusion ($gg$F) and the other being in association with top quarks. The $H \to S h$ decay mode is considered, where leptonic final sates are studied. The CP properties of $S$ are characterised by considering effective couplings derived from dimension six operators through $SW^+W^-$ vertices. The nature of the $S$ boson is considered in two separate contexts. Firstly in a simplified model, it is considered to have Higgs-like couplings. Secondly, we consider a heavy neutrino model and its interactions with the $Z, W^\pm$ and $S$ bosons. The predictions of the model are compared both to ATLAS and CMS results at $\sqrt{s} = 8$ and $13$ TeV. Comparisons to the data are made, when appropriate. The compatibility of the data with the parameters obtained in Ref. \cite{vonBuddenbrock:2015ema} is discussed. A number of regions of the phase-space are suggested to the experiments for further exploration.

  • Neutrino Oscillation Measurements Computed in Quantum Field Theory

    by: Kobach, Andrew
    We use an effective quantum field theory formalism that includes simultaneously the source, detector, and neutrino fields, to study neutrino oscillation experiments. The source and detector are treated in the $1/M$ expansion of heavy particle effective field theory, and the neutrinos have energies much larger than the inverse baseline of the experiment. Within certain limits, we recover the standard oscillation formula used by neutrino experiments. We find a different result for the way in which oscillations become damped for very long baselines, compared with the usual discussion in the literature. Our analysis also provides a pedagogical example of a measurement process in quantum mechanics.

  • Constraining the Compressed Top Squark and Chargino along the W Corridor

    by: Cheng, Hsin-Chia
    Studying superpartner production together with a hard initial state radiation (ISR) jet has been a useful strategy for searches of supersymmetry with a compressed spectrum at the Large Hadron Collider (LHC). In the case of the top squark (stop), the ratio of the missing transverse momentum from the lightest neutralinos and the ISR momentum, defined as $\bar{R}_M$, turns out to be an effective variable to distinguish the signal from the backgrounds. It has helped to exclude the stop mass up to 590 GeV along the top corridor where $m_{\tilde{t}} - m_{\tilde{\chi}_1^0} \approx m_t$. On the other hand, the current experimental limit is still rather weak in the $W$ corridor where $m_{\tilde{t}} - m_{\tilde{\chi}_1^0} \approx m_W +m_b$. In this work we extend this strategy to the parameter region around the $W$ corridor by considering the one lepton final state. In this case the kinematic constraints are insufficient to completely determine the neutrino momentum which is required to calculate $\bar{R}_M$. However, the minimum value of $\bar{R}_M$ consistent with the kinematic constraints still provides a useful discriminating variable, allowing the exclusion reach of the stop mass to be extended to $\sim 550$ GeV based on the current 36 fb$^{-1}$ LHC data. The same method can also be applied to the chargino search with $m_{\tilde{\chi}_1^\pm} -m_{\tilde{\chi}_1^0} \approx m_W$ because the analysis does not rely on $b$ jets. It allows an exclusion reach of the chargino mass up to $\sim 300$ GeV with the current data, beyond the limit obtained from the multilepton search.

  • Leptogenesis Constraints on $B-L$ breaking Higgs Boson in TeV Scale Seesaw Models

    by: Dev, P. S. Bhupal
    In the type-I seesaw mechanism for neutrino masses, there exists a $B-L$ symmetry, whose breaking leads to the lepton number violating mass of the heavy Majorana neutrinos. This would imply the existence of a new neutral scalar associated with the $B-L$ symmetry breaking, analogous to the Higgs boson of the Standard Model. If in such models, the heavy neutrino decays are also responsible for the observed baryon asymmetry of the universe via the leptogenesis mechanism, the new seesaw scalar interactions with the heavy neutrinos will induce additional dilution terms for the heavy neutrino and lepton number densities. We make a detailed study of this dilution effect on the lepton asymmetry in three generic classes of seesaw models with TeV-scale $B-L$ symmetry breaking, namely, in an effective theory framework and in scenarios with global or local $U(1)_{B-L}$ symmetry. We find that requiring successful leptogenesis imposes stringent constraints on the mass and couplings of the new scalar in all three cases, especially when it is lighter than the heavy neutrinos. We also discuss the implications of these new constraints and prospects of testing leptogenesis in presence of seesaw scalars at colliders.

  • Measuring the Sterile Neutrino CP Phase at DUNE and T2HK

    by: Choubey, Sandhya
    The CP phases associated with the sterile neutrino cannot be measured in the dedicated short-baseline experiments being built to test the sterile neutrino hypothesis. On the other hand, these phases can be measured in long-baseline experiments, even though the main goal of these experiments is not to test or measure sterile neutrino parameters. In particular, the sterile neutrino phase $\delta_{24}$ affects the charged-current electron appearance data in long-baseline experiment. In this paper we show for the first time how well the sterile neutrino phase $\delta_{24}$ can be measured by the next-generation long-baseline experiments DUNE, T2HK (and T2HKK). We also show the expected precision with which this sterile phase can be measured by combining the DUNE data with data from T2HK or T2HKK. We also present the sensitivity of these experiments to the sterile mixing angles, both by themselves, as well as when DUNE is combined with T2HK or T2HKK.

  • Scalar Quintuplet Minimal Dark Matter with Yukawa Interactions: Perturbative up to Planck Scale

    by: Cai, Chengfeng
    We confront the perturbativity problem in the real scalar quintuplet minimal dark matter model. In the original model, the quintuplet quartic self-coupling inevitably hits a Landau pole at a scale about 10^{14} GeV, far below the Planck scale. In order to push up this Landau pole scale, we extend the model with a fermionic quintuplet and three fermionic singlets which couple to the scalar quintuplet via Yukawa interactions. Involving such Yukawa interactions at a scale about 10^{10} GeV not only can keep all couplings perturbative up to the Planck scale, but also can explain the smallness of neutrino masses via the type-I seesaw mechanism. Furthermore, we identify the parameter regions favored by the condition that perturbativity and vacuum stability are both maintained up to the Planck scale.

  • Charged lepton flavor violating Higgs decays at the CEPC

    by: Qin, Qin
    The Circular Electron-Positron Collider is proposed by the Chinese high energy community to operate at 240 - 250 GeV and produce about one million Higgs bosons. We evaluate the upper bounds on the branching ratios of the charged lepton flavor violating Higgs decays $H\to e^\pm\mu^\mp$, $e^\pm\tau^\mp$ and $\mu^\pm\tau^\mp$ given by expected measurements at the collider, by simulating the signal samples and corresponding major background samples. The results read $\mathcal{B}(H\to e^\pm\mu^\mp) < 1.2\times 10^{-5}$, $\mathcal{B}(H\to e^\pm\tau^\mp) < 1.6\times 10^{-4}$ and $\mathcal{B}(H\to \mu^\pm\tau^\mp) < 1.4\times 10^{-4}$ at 95\% confidence level. We also give the resulting constraints on the Higgs couplings with the corresponding leptons, the new physics cut-off scales in the Standard Model effective field theory, in Randall-Sundrum models and in models with heavy neutrinos.

  • Positivity bound on the imaginary part of the right-chiral tensor coupling \boldmath{$g_R$} in polarized top quark decay

    by: Groote, S.
    We derive a positivity bound on the right-chiral tensor coupling Im $g_R$ in polarized top quark decay by analyzing the angular decay distribution of the three-body polarized top quark decay $t(\uparrow)\to b+\ell^+ +\nu_\ell$ in NLO QCD. We obtain the bound $-0.0420 \le$ Im $g_R \le 0.0420$.

  • Matter density, symmetry breaking, and neutrino oscillation

    by: Mohseni Sadjadi, H.
    A proposal for the neutrino mass, based on neutrino-scalar field interaction, is introduced. The scalar field, in turn, is nonminimally coupled to the Ricci scalar, and hence relates the neutrino mass to the matter density. In a dense region, the scalar field obeys the $Z_2$ symmetry, and the neutrino is massless. In a diluted region, the $Z_2$ symmetry breaks and neutrino acquires mass from the non-vanishing expectation value of the scalar field. We consider this scenario in the framework of a spherical dense object whose outside is a diluted region. In this background, we study the neutrino flavors oscillation, along with the consequences of the theory on oscillation length and MSW effect. This preliminary model may shed some lights on the existing anomalies within the neutrino data, concerning the different oscillating behavior of the neutrinos in regions with different densities.

  • Reaction rates and transport in neutron stars

    by: Schmitt, Andreas
    Understanding signals from neutron stars requires knowledge about the transport inside the star. We review the transport properties and the underlying reaction rates of dense hadronic and quark matter in the crust and the core of neutron stars and point out open problems and future directions.

  • Quantum field theoretical description of neutrino oscillations and reactor antineutrino anomaly
    Phys.Part.Nucl. 48 (2017) 1007-1010

    by: Naumov, D.V. (Dubna, JINR) et al.

    We suggest a possible explanation of the reactor antineutrino anomaly derived from a covariant quantum field-theoretical approach to neutrino oscillations. Some disadvantages of the currently prevailing interpretation of the anomaly, based upon the sterile neutrino hypothesis are pointed out.

  • Quasielastic neutrino–nucleus interactions in the empirical model of running axial mass of the nucleon
    Phys.Part.Nucl. 48 (2017) 995-997
    Fiz.Elem.Chast.Atom.Yadra 48 (2017)

    by: Kuzmin, K.S. (Dubna, JINR) et al.

    In accelerator neutrino experiments, neutrino-mixing parameters are extracted from the counting rates of quasielastic (anti)neutrino scattering on nuclear targets. We discuss the uncertainties of these rates in the model approach with an energy-dependent (or running) axial mass of the nucleon.

  • Can One have Significant Deviations from Leptonic $3\times 3$ Unitarity in the Framework of Type I Seesaw Mechanism?

    by: Agostinho, Nuno Rosa
    We address the question of deviations from $3\times 3$ unitarity of the leptonic mixing matrix showing that, contrary to conventional wisdom, one may have significant deviations from unitarity in the framework of type I seesaw mechanism. In order for this scenario to be feasible, at least one of the heavy neutrinos must have a mass at the TeV scale, while the other two may have much larger masses. We present specific examples where deviations from $3\times 3$ unitarity are sufficiently small to conform to all the present stringent experimental bounds but are sufficiently large to have the potential for being detectable at the next round of experiments.

  • Revisiting the high-scale validity of Type-II seesaw model with novel LHC signature

    by: Ghosh, Dilip Kumar
    The Type-II seesaw model is a well-motivated new physics scenario to address the origin of the neutrino mass issue. We show that this model can easily accommodate an absolutely stable vacuum until the Planck scale, however with strong limit on the exotic scalar masses and the corresponding mixing angle. We examine the model prediction at the current and future high luminosity run of the Large Hadron Collider (LHC) in such high-scale valid region. Specifically, we device the associated and pair production of the charged scalars as a new probe of the model at the LHC. We show that for a particular signal process the model can be tested with $5\sigma$ signal significance even at the present run of the LHC.

  • Can one ever prove that neutrinos are Dirac particles?

    by: Hirsch, Martin
    According to the "Black Box" theorem the experimental confirmation of neutrinoless double beta decay ($0 \nu 2 \beta$) would imply that at least one of the neutrinos is a Majorana particle. However, a null $0 \nu 2 \beta$ signal cannot decide the nature of neutrinos, as it can be suppressed even for Majorana neutrinos. In this letter we argue that if the null $0 \nu 2 \beta$ decay signal is accompanied by a $0 \nu 4 \beta$ quadruple beta decay signal, then at least one neutrino should be a Dirac particle. This argument holds irrespective of the underlying processes leading to such decays.

  • Exploring a Non-Minimal Sterile Neutrino Model Involving Decay at IceCube and Beyond

    by: Moss, Zander
    We study the phenomenology of neutrino decay together with neutrino oscillations in the context of eV-scale sterile neutrinos. We review the formalism of visible neutrino decay in which one of the decay products is a neutrino that potentially can be observed. We apply the formalism developed for decay to the recent sterile neutrino search performed by IceCube with TeV neutrinos. We show that for $\nu_4$ lifetime $\tau_4/m_4 \lesssim 10^{-16} {\rm eV^{-1}s}$, the interpretation of the high-energy IceCube analysis can be significantly changed.

  • CP violations in $A_4$ symmetry model with two Higgs singlets

    by: Nguyen, T. Phong
    We study a seesaw model with $A_4$ flavor symmetry with two Higgs singlets and it's physics phenomenological consequences. After symmetry breaking, the model leads to the neutrino mixing matrix that satisfies the current data of neutrino oscillation experiments. We then study how the low energy CP violation parameter, $J_{CP}$, associate with the Dirac CP violation phase $\delta$. We also study the high energy CP violation associate with the decay of heavy right handed neutrino in leptogenesis process in order to explain the observed baryon asymmetry of the Universe, $\eta_B$. Numerically, we find a correlation between $J_{CP}$ and $\eta_B$. It is shown that our prediction for $J_{CP}$, and hence for the Dirac CP violating phase $\delta$, for some high energy's fixed parameters can be constrained by the current data of $\eta_B$.

  • A radiative seesaw model with higher order terms under an alternative $U(1)_{B-L}$

    by: Nomura, Takaaki
    We propose a model based on an alternative $U(1)_{B-L}$ gauge symmetry with 5 dimensional operators in the Lagrangian, and we construct the neutrino masses at one-loop level, and discuss lepton flavor violations, dark matter, and the effective number of neutrino species due to two massless particles in our model. Then we search allowed region to satisfy the current experimental data of neutrino oscillation and lepton flavor violations without conflict of several constraints such as stability of dark matter and the effective number of neutrino species, depending on normal hierarchy and inverted one.

  • Probing a Four Flavour vis-a-vis Three Flavour Neutrino Mixing for UHE Neutrino Signals at a 1 ${\rm Km}^2$ Detector

    by: Pandey, Madhurima
    We consider a four flavour scenario for the neutrinos where an extra sterile neutrino is introduced with the three families of active neutrinos and study the deviation from three flavour scenario in the ultra high energy (UHE) regime. We calculate the possible muon and shower yields at a 1 Km$^2$ detector such as ICECUBE for these neutrinos from distant UHE sources namely Gamma Ray Bursts (GRBs) etc. Similar estimations for muon and shower yields are also obtained for three flavour case. Comparing the two results we find considerable differences of the yields for these two cases. This can be useful for probing the existence of a fourth sterile component using UHE neutrino flux.

  • Polarization Transfer in Weak Pion Production off the Nucleon

    by: Graczyk, Krzysztof M.
    Polarization transfer (PT) observables in the single pion production induced by the charged current interaction of the neutrino with the nucleon are examined. The polarization components of the final nucleon and the charged lepton are calculated within two models for the pion production. It is demonstrated that the PT observables, the degree of polarization and the polarization components of outgoing fermions, are sensitive on assumptions about the nonresonant background model. In particular it is shown that the normal components of the polarization of the outgoing nucleon and the lepton are determined by the interference between the resonant (RES) and nonresonant (NB) amplitudes. Moreover the sign of the normal component of the polarization of the charged lepton is fixed by the relative sign between the RES and the NB amplitudes.

  • Challenges posed by non-standard neutrino interactions in the determination of $\delta_{CP}$ at DUNE

    by: Deepthi, K.N.
    One of the primary objectives of Deep Underground Neutrino Experiment (DUNE) is to discover the leptonic CP violation and to identify it's source. In this context, we study the impact of non-standard neutrino interactions (NSIs) on observing the CP violation signal at DUNE. We explore the impact of various parameter degeneracies introduced by non-zero NSI and identify which of these can influence the CP violation sensitivity and CP precision of DUNE, by considering NSI both in data and in theory. In particular, we study how the CP sensitivity of DUNE is affected because of the intrinsic hierarchy degeneracy which occurs when the diagonal NSI parameter $\epsilon_{ee}=-1$ and $\delta_{CP}= \pm 90^{\circ}$.

  • Search for Boosted Dark Matter Interacting With Electrons in Super-Kamiokande

    by: Kachulis, C. (Yokohama Natl. U.) et al.

    A search for boosted dark matter using 161.9 kiloton-years of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic Center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic Center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay.

  • Evidence of Neutrino Enhanced Clustering in a Complete Sample of Sloan Survey Clusters, Implying $\sum m_{\nu}=0.11\pm0.03eV$

    by: Emami, Raizeh
    The clustering amplitude of 7143 clusters from the Sloan Digital Sky Survey (SDSS) is found to increase linearly with cluster mass, closely agreeing with the Gaussian random field hypothesis for structure formation. In detail, the observed correlation length exceeds pure cold dark matter (CDM) simulation predictions by $\simeq 6\%$, for the standard Planck-based values of the cosmological parameters. We show this excess is naturally accounted for by free streaming of light neutrinos, which opposes gravitational growth, so that clusters formed at fixed mass are fewer and hence more biased than for a pure CDM density field. An enhancement in the cluster bias by $7\%$ matches the observations, corresponding to a total neutrino mass, $\sum m_{\nu}=(0.11\pm0.03)eV$, for the standard relic neutrino density. If ongoing laboratory experiments favor a normal neutrino mass hierarchy, then we may infer a somewhat larger total mass than the minimum oscillation based value, $\sum m_{\nu} \simeq 0.056eV$, with $95\%$ confidence. Much higher precision can be achieved by applying our method to the more numerous galaxy groups present in the SDSS, for which we predict an appreciable clustering enhancement by neutrinos.

  • Gravitational Leptogenesis and Reheating

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

    Gravitational leptogenesis is a model of baryogenesis in which the matter-antimatter asymmetry of the universe arises through the standard model lepton-number gravitational anomaly. In this scenario, chiral gravitational waves source standard model neutrino helicity during the inflationary epoch. Since the standard model does not accommodate neutrino flavor oscillation data, it must be extended to provide nonzero neutrino masses. The origin of neutrino mass is presently unknown, and standard model neutrinos could be either Dirac or Majorana fermions. We point out that gravitational leptogenesis can be accommodated in either mass scenario. However, in the case where the light neutrinos are Majorana particles, there is an inherent channel for the washout of lepton-number during post-inflationary reheating. For Majorana neutrinos with the simplest model of reheating, we find that washout can be avoided if the equation of state of the universe during reheating is that of radiation and the standard model is not thermalized until below $T \simeq 1 \times 10^{12}$ GeV.

  • Exclusive neutrino-production of a charmed vector meson and transversity gluon GPDs

    by: Pire, B.
    We calculate at the leading order in $\alpha_s$ the QCD amplitude for exclusive neutrino production of a $D^*$ or $D_s^*$ charmed vector meson on a nucleon. We work in the framework of the collinear QCD approach where generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions. We include $O(m_c)$ terms in the coefficient functions and $O(m_D)$ term in the definition of heavy meson distribution amplitudes. The show that the analysis of the angular distribution of the decay $D_{(s)}^*\to D_{(s)} \pi$ allows to access the transversity gluon GPDs.

  • Stimulated X-rays in resonant atom Majorana mixing

    by: Segarra, A.
    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 short-lived excited state, as well as the ground state of the daughter atom. Their natural population inversion is most appropriate for exploiting the bosonic nature of the observed X-rays by means of stimulating X-ray beams. 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 in a facility like European XFEL.

  • Spin-flavor oscillations of ultrahigh-energy cosmic neutrinos in interstellar space: The role of neutrino magnetic moments
    Phys.Rev. D96 (2017) 103017

    by: Kurashvili, Podist (NCBJ, Swierk) et al.

    A theoretical analysis of possible influence of neutrino magnetic moments on the propagation of ultrahigh-energy cosmic neutrinos in the interstellar space is carried out under the assumption of two-neutrino mixing. The exact solution of the effective equation for neutrino evolution in the presence of a magnetic field and matter is obtained, which accounts for four neutrino species corresponding to two different flavor states with positive and negative helicities. Using most stringent astrophysical bounds on the putative neutrino magnetic moment, probabilities of neutrino flavor and spin oscillations are calculated on the basis of the obtained exact solution. Specific patterns of spin-flavor oscillations are determined for neutrino-energy values characteristic of, respectively, the cosmogenic neutrinos, the Greisen-Zatsepin-Kuz'min (GZK) cutoff, and well above the cutoff.

  • Progress in high-energy cosmic ray physics
    Prog.Part.Nucl.Phys. 98 (2018) 85-118

    by: Mollerach, S. (Centro Atomico Bariloche) et al.

    We review some of the recent progress in our knowledge about high-energy cosmic rays, with an emphasis on the interpretation of the different observational results. We discuss the effects that are relevant to shape the cosmic ray spectrum and the explanations proposed to account for its features and for the observed changes in composition. The physics of air-showers is summarized and we also present the results obtained on the proton–air cross section and on the muon content of the showers. We discuss the cosmic ray propagation through magnetic fields, the effects of diffusion and of magnetic lensing, the cosmic ray interactions with background radiation fields and the production of secondary neutrinos and photons. We also consider the cosmic ray anisotropies, both at large and small angular scales, presenting the results obtained from the TeV up to the highest energies and discuss the models proposed to explain their origin.

  • Nuclear medium effects in muonic neutrino interaction with energies from 0.2 GeV to 1.5 GeV
    Phys.Rev. C96 (2017) 054606

    by: Vargas, D. (Santa Cruz U., DCET) et al.

    Nuclear reactions induced by muon neutrinos with energies from 0.2 to 1.5 GeV in the Monte Carlo calculation framework in the intranuclear cascade model are studied. This study was done by comparing the available experimental data and theoretical values of total cross section, and the energy distribution of emitted lepton energy in the reaction muon neutrino nucleus, using the targets C12, O16, Al27, Ar40, Fe56, and Pb208. A phenomenological model of primary neutrino-nucleon interaction gives good agreement between our theoretical inclusive neutrino nucleus cross section and the available experimental data. Some interesting results on the behavior of the cross section as function of 1p-1n and higher contributions are also sketched. The previous results on the fraction of fake events in available experiments in C12 were expanded for the set of studied nuclei. With the increase of mass targets, the nuclear effects in the cross sections were observed and the importance of taking into account fake events in the reactions was noted.

  • Majorana neutrino signals at Belle-II and ILC
    Nucl.Phys. B925 (2017) 186-194

    by: Yue, Chong-Xing (Liaoning Normal U.) et al.

    For some theoretical and experimental considerations, the relatively light Majorana neutrinos at the GeV scale have been attracting some interest. In this article we consider a scenario with only one Majorana neutrino N , negligible mixing with the active neutrinos νL , where the Majorana neutrino interactions could be described in a model independent approach based on an effective theory. Under such a framework, we particularly study the feasibility of observing the N with mass in the range 0–30 GeV via the process e+e−→νN→γ+E̸ in the future Belle-II and ILC experiments. The results show that it is unpromising for Belle-II to observe the signal, while ILC may easily make a discovery for the Majorana neutrino.

  • Multimessenger tests of the weak equivalence principle from GW170817 and its electromagnetic counterparts
    JCAP 1711 (2017) 035

    by: Wei, Jun-Jie (Purple Mountain Observ.) et al.

    The coincident detection of a gravitational-wave (GW) event GW170817 with electromagnetic (EM) signals (e.g., a short gamma-ray burst SGRB 170817A or a macronova) from a binary neutron star merger within the nearby galaxy NGC 4933 provides a new, multimessenger test of the weak equivalence principle (WEP), extending the WEP test with GWs and photons. Assuming that the arrival time delay between the GW signals from GW170817 and the photons from SGRB 170817A or the macronova is mainly attributed to the gravitational potential of the Milky Way, we demonstrate that the strict upper limits on the deviation from the WEP are Δγ < 1.4 × 10−3 for GW170817/macronova and Δγ < 5.9 × 10−8 for GW170817/SGRB 170817A. A much more severe constraint on the WEP accuracy can be achieved (~ 0.9 × 10−10) for GW170817/SGRB 170817A when we consider the gravitational potential of the Virgo Cluster, rather than the Milky Way's gravity. This provides the tightest limit to date on the WEP through the relative differential variations of the γ parameter for two different species of particles. Compared with other multimessenger (photons and neutrinos) results, our limit is 7 orders of magnitude tighter than that placed by the neutrinos and photons from supernova 1987A, and is almost as good as or is an improvement of 6 orders of magnitude over the limits obtained by the low-significance neutrinos correlated with GRBs and a blazar flare.

  • Neutrino oscillations: the rise of the PMNS paradigm
    Prog.Part.Nucl.Phys. 98 (2018) 1-54

    by: Giganti, Claudio (Paris U., VI-VII) et al.

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

  • New Physics effect on $B_c \to J/\psi \tau\bar\nu$ in relation to the $R_{D^{(*)}}$ anomaly
    Phys.Lett. B776 (2018) 5-9

    by: Watanabe, Ryoutaro (Montreal U.)

    We study possible new physics (NP) effects on Bc→J/ψτν¯ , which has been recently measured at LHCb as the ratio of RJ/ψ=B(Bc→J/ψτν¯)/B(Bc→J/ψμν¯) . Combining it with the long-standing RD(⁎) measurements, in which the discrepancy with the prediction of the standard model is present, we find possible solutions to the anomaly by several NP types. Then, we see that adding the RJ/ψ measurement does not improve NP fit to data, but the NP scenarios still give better χ2 than the SM. We also investigate indirect NP constraints from the lifetime of Bc and NP predictions on the τ longitudinal polarization in B¯→D⁎τν¯ .

  • Freeze-out of baryon number in low-scale leptogenesis
    JCAP 1711 (2017) 030

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

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

  • Neutrino vs. Antineutrino Oscillation Parameters at DUNE and Hyper-Kamiokande
    Phys.Rev. D96 (2017) 095018

    by: de Gouvêa, André (Northwestern U.) et al.

    Testing, in a nontrivial, model-independent way, the hypothesis that the three-massive-neutrinos paradigm properly describes nature is among the main goals of the current and the next generation of neutrino oscillation experiments. In the coming decade, the DUNE and Hyper-Kamiokande experiments will be able to study the oscillation of both neutrinos and antineutrinos with unprecedented precision. We explore the ability of these experiments, and combinations of them, to determine whether the parameters that govern these oscillations are the same for neutrinos and antineutrinos, as prescribed by the CPT-theorem. We find that both DUNE and Hyper-Kamiokande will be sensitive to unexplored levels of leptonic CPT-violation. Assuming the parameters for neutrino and antineutrino oscillations are unrelated, we discuss the ability of these experiments to determine the neutrino and antineutrino mass-hierarchies, atmospheric-mixing octants, and CP-odd phases, three key milestones of the experimental neutrino physics program. Additionally, if the CPT-symmetry is violated in nature in a way that is consistent with all present neutrino and antineutrino oscillation data, we find that DUNE and Hyper-Kamiokande have the potential to ultimately establish leptonic CPT-invariance violation.

  • Sterile neutrinos or flux uncertainties? — Status of the reactor anti-neutrino anomaly
    JHEP 1711 (2017) 099

    by: Dentler, Mona (Mainz U.) et al.

    The ∼ 3σ discrepancy between the predicted and observed reactor anti-neutrino flux, known as the reactor anti-neutrino anomaly, continues to intrigue. The recent discovery of an unexpected bump in the reactor anti-neutrino spectrum, as well as indications that the flux deficit is different for different fission isotopes seems to disfavour the explanation of the anomaly in terms of sterile neutrino oscillations. We critically review this conclusion in view of all available data on electron (anti)neutrino disappearance. We find that the sterile neutrino hypothesis cannot be rejected based on global data and is only mildly disfavored compared to an individual rescaling of neutrino fluxes from different fission isotopes. The main reason for this is the presence of spectral features in recent data from the NEOS and DANSS experiments. If state-of-the-art predictions for reactor fluxes are taken at face value, sterile neutrino oscillations allow a consistent description of global data with a significance close to 3σ relative to the no-oscillation case. Even if reactor fluxes and spectra are left free in the fit, a 2σ hint in favour of sterile neutrinos remains, with allowed parameter regions consistent with an explanation of the anomaly in terms of oscillations.

  • Towards the minimal seesaw model via CP violation of neutrinos
    JHEP 1711 (2017) 201

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

    We study the minimal seesaw model, where two right-handed Majorana neutrinos are introduced, focusing on the CP violating phase. In addition, we take the trimaximal mixing pattern for the neutrino flavor where the charged lepton mass matrix is diagonal. Owing to this symmetric framework, the 3 × 2 Dirac neutrino mass matrix is given in terms of a few parameters. It is found that the observation of the CP violating phase determines the flavor structure of the Dirac neutrino mass matrix in the minimal seesaw model. New minimal Dirac neutrino mass matrices are presented in the case of TM$_{1}$, which is given by the additional 2-3 family mixing to the tri-bimaximal mixing basis in the normal hierarchy of neutrino masses. Our model includes the Littlest seesaw model by King et al. as one of the specific cases. Furthermore, it is remarked that our 3 × 2 Dirac neutrino mass matrix is reproduced by introducing gauge singlet flavons with the specific alignments of the VEV’s. These alignments are derived from the residual symmetry of S$_{4}$ group.

  • Phenomenological Analysis of an $\mathrm{E}_{6}$-inspired Seesaw Model
    Phys.Rev. D96 (2017) 095016

    by: Ellis, Joshua P. (ARC, CoEPP, Melbourne) et al.

    We analyze the phenomenology of a model of neutrino masses inspired by unification in E6 in which the exotic neutrinos can be present at low scales. The model introduces vector-like isosinglet down-type quarks, vector-like isodoublet leptons, neutrino singlets and two Z′ bosons. The seesaw mechanism can be achieved with exotic neutrino masses as low as 100 GeV and Yukawa couplings of order 10-3. We find that the lightest Z′ boson mass is required to be above 2.8 TeV, the exotic quark masses are required to be above 1.3 TeV (810 GeV) if they are collider stable (promptly decaying), and the exotic lepton mass bounds remain at the LEP value of 102 GeV. The model also presents a type-II two-Higgs-doublet model (2HDM) along with two heavy singlet scalars. The 2HDM naturally has the alignment limit enforced thanks to the large vacuum expectation values of the exotic scalars, thereby avoiding most constraints.

  • Generalized parton distributions from charged current meson production in $ep$ experiments
    Phys.Rev. D96 (2017) 096006

    by: Siddikov, Marat (CCTVal, Valparaiso) et al.

    We suggest that generalized parton distributions (GPDs) can be probed in the charged current meson production process, ep→νeπ-p. In contrast to pion photoproduction, this process is sensitive to the unpolarized GPDs H, E, and for this reason has a very small contamination by higher twist and Bethe-Heitler type contributions. Since all produced hadrons are charged, we expect that the kinematics of this process could be reconstructed from experiment. We estimated the cross sections in the kinematics of upgraded 12 GeV Jefferson Laboratory experiments and found that thanks to large luminosity the process can be measured with reasonable statistics.

  • Unified Scenario for Composite Right-Handed Neutrinos and Dark Matter
    Phys.Rev. D96 (2017) 115003

    by: Davoudiasl, Hooman (Brookhaven Natl. Lab.) et al.

    We entertain the possibility that neutrino masses and dark matter (DM) originate from a common composite dark sector. A minimal effective theory can be constructed based on a dark $SU(3)_D$ interaction with three flavors of massless dark quarks; electroweak symmetry breaking gives masses to the dark quarks. By assigning a $\mathbb Z_2$ charge to one flavor, a stable "dark kaon" can provide a good thermal relic DM candidate. We find that "dark neutrons" may be identified as right handed Dirac neutrinos. Some level of "neutron-anti-neutron" oscillation in the dark sector can then result in non-zero Majorana masses for light Standard Model neutrinos. A simple ultraviolet completion is presented, involving additional heavy $SU(3)_D$-charged particles with electroweak and lepton Yukawa couplings. At our benchmark point, there are "dark pions" that are much lighter than the Higgs and we expect spectacular collider signals arising from the UV framework. This includes the decay of the Higgs boson to $\tau \tau \ell \ell'$, where $\ell$($\ell'$) can be any lepton, with displaced vertices. We discuss the observational signatures of this UV framework in dark matter searches and primordial gravitational wave experiments; the latter signature is potentially correlated with the $H \to \tau \tau \ell \ell'$ decay.

  • Neutrinos in Large Extra Dimensions and Short-Baseline $\nu_e$ Appearance
    Phys.Rev. D96 (2017) 095014

    by: Carena, Marcela (Chicago U., EFI) et al.

    We show that, in the presence of bulk masses, sterile neutrinos propagating in large extra dimensions (LED) can induce electron-neutrino appearance effects. This is in contrast to what happens in the standard LED scenario, and hence LED models with explicit bulk masses have the potential to address the MiniBooNE and LSND appearance results as well as the reactor and Gallium anomalies. A special feature in our scenario is that the mixing of the first Kaluza-Klein modes to active neutrinos can be suppressed, making the contribution of heavier sterile neutrinos to oscillations relatively more important. We study the implications of this neutrino mass generation mechanism for current and future neutrino oscillation experiments and show that the Short Baseline Neutrino Program at Fermilab will be able to efficiently probe such a scenario. In addition, this framework leads to massive Dirac neutrinos and thus precludes any signal in neutrinoless double beta decay experiments.

  • The $\mu-\tau$ reflection symmetry of Dirac neutrinos and its breaking effect via quantum corrections
    JHEP 1711 (2017) 135

    by: Xing, Zhi-zhong (Beijing, Inst. High Energy Phys.) et al.

    Given the Dirac neutrino mass term, we explore the constraint conditions which allow the corresponding mass matrix to be invariant under the \mu-\tau reflection transformation, leading us to the phenomenologically favored predictions \theta_{23} = \pi/4 and \delta = 3\pi/2 in the standard parametrization of the 3\times 3 lepton flavor mixing matrix. If such a flavor symmetry is realized at a superhigh energy scale \Lambda_{\mu\tau}, we investigate how it is spontaneously broken via the one-loop renormalization-group equations (RGEs) running from \Lambda_{\mu\tau} down to the Fermi scale \Lambda_{\rm F}. Such quantum corrections to the neutrino masses and flavor mixing parameters are derived, and an analytical link is established between the Jarlskog invariants of CP violation at \Lambda_{\mu\tau} and \Lambda_{\rm F}. Some numerical examples are also presented in both the minimal supersymmetric standard model and the type-II two-Higgs-doublet model, to illustrate how the octant of \theta_{23}, the quadrant of \delta and the neutrino mass ordering are correlated with one another as a result of the RGE-induced \mu-\tau reflection symmetry breaking effects.

  • LHC Run I Bounds on Minimal Lepton Flavour Violation in Type-III See-saw: A Case Study
    JHEP 1711 (2017) 118

    by: Agostinho, Nuno Rosa (Barcelona U.) et al.

    We study the bounds on minimal lepton flavour violation in the context of Type-III see-saw imposed by LHC Run I search for events which contain two charged leptons (either electron or muons of equal or opposite sign), two jets from a hadronically decaying $W$ boson and large missing transverse momentum. In this scenario the flavour structure of the couplings of the triplet fermions to the Standard Model leptons can be reconstructed from the neutrino mass matrix and lepton number violation is very suppressed. We find that using the information on charge and flavour of the leptons in the above final state it is possible to unambiguously rule out this scenario with triplet masses lighter than 300 GeV at 95% CL. The same analysis allows to exclude triplet masses masses up to 480 GeV at 95% CL for normal ordering of neutrino masses and specific values of a Majorana CP phase currently undetermined by neutrino physics.

  • Fundamental physics from future weak-lensing calibrated Sunyaev-Zel’dovich galaxy cluster counts
    Phys.Rev. D96 (2017) 103525

    by: Madhavacheril, Mathew S. (Princeton U., Astrophys. Sci. Dept.) et al.

    Future high-resolution measurements of the cosmic microwave background (CMB) will produce catalogs of tens of thousands of galaxy clusters through the thermal Sunyaev-Zel’dovich (tSZ) effect. We forecast how well different configurations of a CMB Stage-4 experiment can constrain cosmological parameters, in particular, the amplitude of structure as a function of redshift σ8(z), the sum of neutrino masses Σmν, and the dark energy equation of state w(z). A key element of this effort is calibrating the tSZ scaling relation by measuring the lensing signal around clusters. We examine how the mass calibration from future optical surveys like the Large Synoptic Survey Telescope (LSST) compares with a purely internal calibration using lensing of the CMB itself. We find that, due to its high-redshift leverage, internal calibration gives constraints on cosmological parameters comparable to the optical calibration, and can be used as a cross-check of systematics in the optical measurement. We also show that in contrast to the constraints using the CMB lensing power spectrum, lensing-calibrated tSZ cluster counts can detect a minimal Σmν at the 3–5σ level even when the dark energy equation of state is freed up.

  • Decoherence, matter effect, and neutrino hierarchy signature in long baseline experiments
    Phys.Rev. D96 (2017) 093009

    by: Coelho, João A.B. (Tufts U.) et al.

    Environmental decoherence of oscillating neutrinos of strength Γ=(2.3±1.1)×10-23  GeV can explain how maximal θ23 mixing observed at 295 km by T2K appears to be nonmaximal at longer baselines. As shown recently by R. Oliveira, the Mikheyev-Smirnov-Wolfenstein matter effect for neutrinos is altered by decoherence: in normal (inverted) mass hierarchy, a resonant enhancement of νμ(ν¯μ)→νe(ν¯e) occurs for 6
  • Reactor and atmospheric neutrino mixing angles’ correlation as a probe for new physics
    Phys.Rev. D96 (2017) 095021

    by: Pasquini, Pedro (Campinas State U.)

    We perform a simulation on the DUNE experiment to probe the capability of future neutrino long-baseline experiments to constrain the parameter space of high-energy models by using the correlation between the atmospheric and reactor mixing angles. As an example, we analyze the tetrahedral flavor symmetry model, which predicts a strong relation between the nonzero value of θ13 and a deviation of θ23 from maximality. We show that in this case, the model can realistically be excluded by more than 3σ for most of the parameter space. We also study the octant degeneracy at DUNE and its impact on the sensitivity of such models.

  • COHERENT constraints on nonstandard neutrino interactions
    Phys.Lett. B775 (2017) 54-57

    by: Liao, Jiajun (U. Hawaii, Honolulu) et al.

    Coherent elastic neutrino-nucleus scattering consistent with the standard model has been observed by the COHERENT experiment. We study nonstandard neutrino interactions using the detected spectrum. For the case in which the nonstandard interactions (NSI) are induced by a vector mediator lighter than 50 MeV, we obtain constraints on the coupling of the mediator. For a heavier mediator, we find that degeneracies between the NSI parameters severely weaken the constraints. However, these degeneracies do not affect COHERENT constraints on the effective NSI parameters for matter propagation in the Earth.

  • Mapping the dominant regions of the phase space associated with $c\bar c$ production relevant for the prompt atmospheric neutrino flux
    Phys.Rev. D96 (2017) 094026

    by: Goncalves, Victor P. (Pelotas U.) et al.

    We present a detailed mapping of the dominant kinematical domains contributing to the prompt atmospheric neutrino flux at high neutrino energies by studying their sensitivity to the cuts on several kinematical variables crucial for charm production in cosmic ray scattering in the atmosphere. This includes the maximal center-of-mass energy for proton-proton scattering, the longitudinal momentum fractions of partons in the projectile (cosmic ray) and target (nucleus of the atmosphere), the Feynman xF variable, and the transverse momentum of charm quark/antiquark. We find that the production of neutrinos with energies larger than Eν>107  GeV is particularly sensitive to the c.m. energies larger than the ones at the LHC and to the longitudinal momentum fractions in the projectile 10-8
  • Neutrino mass with large $SU(2)_L$ multiplet fields
    Phys.Rev. D96 (2017) 095017

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

    We propose an extension of the standard model introducing large SU(2)L multiplet fields which are quartet and septet scalars and quintet Majorana fermions. These multiplets can induce the neutrino masses via interactions with the SU(2) doublet leptons. We then find the neutrino masses are suppressed by a small vacuum expectation value of the quartet/septet and an inverse of the quintet fermion mass, relaxing the Yukawa hierarchies among the standard model fermions. We also discuss collider physics at the Large Hadron Collider, considering the production of charged particles in these multiplets, and due to the effects of violating the custodial symmetry, some specific signatures can be found. Then, we discuss the detectability of these signals.

  • $Z\gamma$ production at NNLO including anomalous couplings
    JHEP 1711 (2017) 150

    by: Campbell, John M. (Fermilab) et al.

    In this paper we present a next-to-next-to-leading order (NNLO) QCD calculation of the processes $pp\rightarrow l^+l^-\gamma$ and $pp\rightarrow \nu\bar\nu\gamma$ that we have implemented in MCFM. Our calculation includes QCD corrections at NNLO both for the Standard Model (SM) and additionally in the presence of $Z\gamma\gamma$ and $ZZ\gamma$ anomalous couplings. We compare our implementation, obtained using the jettiness slicing approach, with a previous SM calculation and find broad agreement. Focusing on the sensitivity of our results to the slicing parameter, we show that using our setup we are able to compute NNLO cross sections with numerical uncertainties of about $0.1\%$, which is small compared to residual scale uncertainties of a few percent. We study potential improvements using two different jettiness definitions and the inclusion of power corrections. At $\sqrt{s}=13$ TeV we present phenomenological results and consider $Z\gamma$ as a background to $H\to Z\gamma$ production. We find that, with typical cuts, the inclusion of NNLO corrections represents a small effect and loosens the extraction of limits on anomalous couplings by about $10\%$.

  • What measurements of neutrino neutral current events can reveal
    JHEP 1711 (2017) 202

    by: Gandhi, Raj (Harish-Chandra Res. Inst.) et al.

    We show that neutral current (NC) measurements at neutrino detectors can play a valuable role in the search for new physics. Such measurements have certain intrinsic features and advantages that can fruitfully be combined with the usual well-studied charged lepton detection channels in order to probe the presence of new interactions or new light states. In addition to the fact that NC events are immune to uncertainties in standard model neutrino mixing and mass parameters, they can have small matter effects and superior rates since all three flavours participate. We also show, as a general feature, that NC measurements provide access to different combinations of CP phases and mixing parameters compared to CC measurements at both long and short baseline experiments. Using the Deep Underground Neutrino Experiment (DUNE) as an illustrative setting, we demonstrate the capability of NC measurements to break degeneracies arising in CC measurements, allowing us, in principle, to distinguish between new physics that violates three flavour unitarity and that which does not. Finally, we show that NC measurements can enable us to restrict new physics parameters that are not easily constrained by CC measurements.

  • Structure of Right-Handed Neutrino Mass Matrix
    Phys.Rev. D96 (2017) 095005

    by: Koide, Yoshio (Osaka U.)

    Recently, Nishiura and the author proposed a unified quark-lepton mass matrix model under a family symmetry U(3)×U(3)′. The model can give excellent parameter fitting to the observed quark and neutrino data. The model has a reasonable basis as far as the quark sector, but, in the neutrino sector, the form of the right-handed neutrino mass matrix MR does not have a theoretical basis; that is, it was nothing but a phenomenological assumption. In this paper, it is pointed out that the form of MR is originated in the structure of Majorana mass matrix (4×4 matrix) for the left-handed fields ((νL)i,(νRc)i,(NL)α,(NRc)α) where νi (i=1, 2, 3) and Nα (α=1, 2, 3) are U(3)-family and U(3)′-family triplets, respectively.

  • Measuring the neutron star compactness and binding energy with supernova neutrinos
    JCAP 1711 (2017) 036

    by: Gallo Rosso, Andrea (Gran Sasso) et al.

    We investigate the precision with which a neutron star gravitational binding energy can be measured through the supernova neutrino signal, without assuming any prior such as the energy equipartition hypothesis, mean energies hierarchy or constraints on the pinching parameters that characterize the neutrino spectra. We consider water Cherenkov detectors and prove that combining inverse beta decay with elastic scattering on electrons is sufficient to reach 11% precision on the neutron star gravitational binding energy already with Super-Kamiokande. The inclusion of neutral current events on oxygen in the analysis does not improve the precision significantly, due to theoretical uncertainties. We examine the possible impact on the conclusion of further theoretical input and of higher statistics. We discuss the implications of our findings on the properties of the newly formed neutron star, in particular concerning the assessment of the compactness or mass-radius relation.

  • Limiting neutrino magnetic moments with Borexino Phase-II solar neutrino data
    Phys.Rev. D96 (2017) 091103

    by: Agostini, M. (GSSI, Aquila) et al.

    A search for the solar neutrino effective magnetic moment has been performed using data from 1291.5 days exposure during the second phase of the Borexino experiment. No significant deviations from the expected shape of the electron recoil spectrum from solar neutrinos have been found, and a new upper limit on the effective neutrino magnetic moment of μνeff<2.8×10-11 μB at 90% C.L. has been set using constraints on the sum of the solar neutrino fluxes implied by the radiochemical gallium experiments. Using the limit for the effective neutrino moment, new limits for the magnetic moments of the neutrino flavor states, and for the elements of the neutrino magnetic moments matrix for Dirac and Majorana neutrinos, are derived.

  • Double-Cascade Events from New Physics in Icecube
    Phys.Rev.Lett. 119 (2017) 201804

    by: Coloma, Pilar (Fermilab) et al.

    A variety of new physics models allows for neutrinos to up-scatter into heavier states. If the incident neutrino is energetic enough, the heavy neutrino may travel some distance before decaying. In this work, we consider the atmospheric neutrino flux as a source of such events. At IceCube, this would lead to a “double-bang” (DB) event topology, similar to what is predicted to occur for tau neutrinos at ultrahigh energies. The DB event topology has an extremely low background rate from coincident atmospheric cascades, making this a distinctive signature of new physics. Our results indicate that IceCube should already be able to derive new competitive constraints on models with GeV-scale sterile neutrinos using existing data.

  • Cosmology and CPT violating neutrinos
    Eur.Phys.J. C77 (2017) 766

    by: Barenboim, Gabriela (Valencia U.) et al.

    The combination charge conjugation–parity–time reversal (CPT) is a fundamental symmetry in our current understanding of nature. As such, testing CPT violation is a strongly motivated path to explore new physics. In this paper we study CPT violation in the neutrino sector, giving for the first time a bound, for a fundamental particle, in the CPT violating particle-antiparticle gravitational mass difference. We argue that cosmology is nowadays the only data sensitive to CPT violation for the neutrino–antineutrino mass splitting and we use the latest data release from Planck combined with the current baryonic-acoustic-oscillation measurement to perform a full cosmological analysis. To show the potential of the future experiments we also show the results for Euclid, a next generation large scale structure experiment.

  • Radiative Left-Right Dirac Neutrino Mass
    Phys.Lett. B776 (2018) 54-57

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

    We consider the conventional left-right gauge extension of the standard model of quarks and leptons without a scalar bidoublet. We study systematically how one-loop radiative Dirac neutrino masses may be obtained. In addition to two well-known cases from almost 30 years ago, we find two new scenarios with verifiable predictions.

  • Clockwork seesaw mechanisms
    Phys.Lett. B776 (2018) 222-226

    by: Park, Seong Chan (IPAP, Seoul) et al.

    We propose new mechanisms for small neutrino masses based on clockwork mechanism. The Standard Model neutrinos and lepton number violating operators communicate through the zero mode of clockwork gears, one of the two couplings of the zero mode is exponentially suppressed by clockwork mechanism. Including all known examples for the clockwork realization of the neutrino masses, different types of models are realized depending on the profile and chirality of the zero mode fermion. Each type of realization would have phenomenologically distinctive features with the accompanying heavy neutrinos.

  • Signatures of Compact Halos of Sterile-Neutrino Dark Matter
    Phys.Rev. D96 (2017) 103020

    by: Kuhnel, Florian (Royal Inst. Tech., Stockholm) et al.

    We investigate compact halos of sterile-neutrino dark matter and examine observable signatures with respect to neutrino and photon emission. Primarily, we consider two cases: primordial black-hole halos and ultracompact minihalos. In both cases, we find that there exists a broad range of possible parameter choices such that detection in the near future with x-ray and gamma-ray telescopes might be well possible. In fact, for energies above 10 TeV, the neutrino telescope IceCube would be a splendid detection machine for such macroscopic dark-matter candidates.

  • Neutrino mass ordering and \mu-\tau reflection symmetry breaking
    Chin.Phys. C41 (2017) 123103

    by: Xing, Zhi-zhong (Beijing, Inst. High Energy Phys.) et al.

    If the neutrino mass spectrum turns out to be m^{}_3 < m^{}_1 < m^{}_2, one may choose to relabel it as m^{\prime}_1 < m^{\prime}_2 < m^{\prime}_3 such that all the masses of fundamental fermions with the same electrical charges are in order. In this case the columns of the 3\times 3 lepton flavor mixing matrix U should be reordered accordingly, and the resulting pattern U^\prime may involve one or two large mixing angles in the standard parametrization or its variations. Since the Majorana neutrino mass matrix keeps unchanged in such a mass relabeling, a possible \mu-\tau reflection symmetry is respected in this connection and its breaking effects are model-independently constrained at the 3\sigma level by using current experimental data.

  • Neutrino mass generation and leptogenesis via pseudo-Nambu-Goldstone Higgs portal
    Phys.Rev. D96 (2017) 095015

    by: Alanne, Tommi (Southern Denmark U., CP3-Origins) et al.

    We consider an extension of the Standard Model with the global symmetry-breaking pattern SO(5)/SO(4), where the Higgs boson arises as a pseudo-Nambu-Goldstone boson. The scalar content of the theory consists of a Standard-Model-like Higgs field and an extra real scalar field. The flavor sector of the model is extended by two right-handed neutrinos compatible with the observed light-neutrino phenomenology, and we find that the correct vacuum alignment determines the mass of the heavier neutrino eigenstate to be around 80 TeV. The new singlet-scalar state generates dynamically a Majorana mass term for the heavy-neutrino states. We show how the model leads to the correct baryon asymmetry of the Universe via leptogenesis in the case of two degenerate or hierarchical heavy neutrinos.

  • A Search for Low-energy Neutrinos Correlated with Gravitational Wave Events GW 150914, GW 151226, and GW 170104 with the Borexino Detector
    Astrophys.J. 850 (2017) 21

    by: Agostini, M. (GSSI, Aquila) et al.

    We present the results of a low-energy neutrino search using the Borexino detector in coincidence with the gravitational wave (GW) events GW 150914, GW 151226, and GW 170104. We searched for correlated neutrino events with visible energies greater than 250 keV within a time window of ±500 s centered around the GW detection time. A total of five candidates were found for all three GW events combined. This is consistent with the expected number of solar neutrino and background events. As a result, we have obtained the best current upper limits on all flavor neutrino () fluence associated with GW events, in the neutrino energy range 0.5–5.0 MeV.

  • Neutrino signal from pair-instability supernovae
    Phys.Rev. D96 (2017) 103008

    by: Wright, Warren P. (North Carolina State U.) et al.

    A very massive star with a carbon-oxygen core in the range of 64  M⊙
  • Constraining Neutrino Masses, the Cosmological Constant and BSM Physics from the Weak Gravity Conjecture
    JHEP 1711 (2017) 066

    by: Ibanez, Luis E. (Madrid, IFT) et al.

    It is known that there are AdS vacua obtained from compactifying the SM to 2 or 3 dimensions. The existence of such vacua depends on the value of neutrino masses through the Casimir effect. Using the Weak Gravity Conjecture, it has been recently argued by Ooguri and Vafa that such vacua are incompatible with the SM embedding into a consistent theory of quantum gravity. We study the limits obtained for both the cosmological constant Λ$_{4}$ and neutrino masses from the absence of such dangerous 3D and 2D SM AdS vacua. One interesting implication is that Λ$_{4}$ is bounded to be larger than a scale of order m$_{ν}^{4}$ , as observed experimentally. Interestingly, this is the first argument implying a non-vanishing Λ$_{4}$ only on the basis of particle physics, with no cosmological input. Conversely, the observed Λ$_{4}$ implies strong constraints on neutrino masses in the SM and also for some BSM extensions including extra Weyl or Dirac spinors, gravitinos and axions. The upper bounds obtained for neutrino masses imply (for fixed neutrino Yukawa and Λ$_{4}$) the existence of upper bounds on the EW scale. In the case of massive Majorana neutrinos with a see-saw mechanism associated to a large scale M ≃ 10$^{10 − 14}$ GeV and Y$_{ν1}$ ≃ 10$^{−3}$, one obtains that the EW scale cannot exceed M$_{EW}$ ≲ 10$^{2}$ − 10$^{4}$ GeV. From this point of view, the delicate fine-tuning required to get a small EW scale would be a mirage, since parameters yielding higher EW scales would be in the swampland and would not count as possible consistent theories. This would bring a new perspective into the issue of the EW hierarchy.

  • Vector Boson Fusion versus Gluon Fusion
    Phys.Rev. D96 (2017) 096009

    by: Chan, Chen-Hsun (Taiwan, Natl. Tsing Hua U.) et al.

    Vector-boson fusion (VBF) is a clean probe of the electroweak-symmetry breaking (EWSB), which inevitably suffers from some level of contamination due to the gluon fusion (ggF). In addition to the jet variables used in the current experimental analysis, we analyze a few more jet-shape variables defined by the girth and integrated jet shape. Taking H→WW*→eνμν and H→γγ as examples, we perform the analysis with a new technique of the two-step boosted-decision-tree method, which significantly reduces the contamination of the ggF in the VBF sample, thus, providing a clean environment in probing the EWSB sector.

  • High energy neutrinos from the Sun
    Astropart.Phys. 97 (2018) 63-68

    by: Masip, M. (CAFPE, Granada)

    The Sun is a main source of high energy neutrinos. These neutrinos appear as secondary particles after the Sun absorbs high-energy cosmic rays, that find there a low-density environment (much thinner than our atmosphere) where most secondary pions, kaons and muons can decay before they lose energy. The main uncertainty in a calculation of the solar neutrino flux is due to the effects of the magnetic fields on the absorption rate of charged cosmic rays. We use recent data from HAWC on the cosmic-ray shadow of the Sun to estimate this rate. We evaluate the solar neutrino flux and show that at 1 TeV it is over ten times larger than the atmospheric one at zenith θz=30∘/150∘ . The flux that we obtain has a distinct spectrum and flavor composition: it is harder and richer in antineutrinos and tau/electron neutrinos than the atmospheric background. This solar flux could be detected in current and upcoming neutrino telescopes. KM3NeT, in particular, looks very promising: it will see the Sun high in the sky (the atmospheric flux is lower there than near the horizon) and expects a very good angular resolution (the Sun’s radius is just 0.27°).

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