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  • Lepton Flavor Violation in a $Z^\prime$ model for the $b \to s$ anomalies

    by: Rocha-Moran, Paulina
    In recent years, several observables associated to semileptonic $b \to s$ processes have been found to depart from their predicted values in the Standard Model, including a few tantalizing hints of lepton flavor universality violation. In this work we consider an existing model with a massive $Z^\prime$ boson that addresses the anomalies in $b \to s$ transitions and extend it with a non-trivial embedding of neutrino masses. We analyze lepton flavor violating effects, induced by the non-universal interaction associated to the $b \to s$ anomalies and by the new physics associated to the neutrino mass generation, and determine the expected ranges for the most relevant observables.

  • General Neutrino Interactions at the DUNE Near Detector

    by: Bischer, Ingolf
    We consider the effect of general neutrino interactions (scalar, vector, pseudoscalar, axial vector and tensor) in neutrino-electron scattering at the DUNE near detector. Those interactions can be associated with heavy new physics and their effect is to cause distortions in the recoil spectrum of the electrons. We show that for some cases energy scales up to 9 TeV are accessible after a 5 year run and that current bounds on interaction parameters can be improved by up to an order of magnitude. The full set of general interactions includes the usually considered neutrino-electron non-standard matter interactions, and the near detector will give limits comparable but complementary to the ones from the analysis of neutrino oscillations in the far detector.

  • Lorentz violation from gamma-ray burst neutrinos
    APS Physics 1 (2018) 62

    by: Huang, Yanqi (Peking U.) et al.

    The Lorentz violation~(LV) effect of ultra-relativistic particles can be tested by gamma-ray burst~(GRB) neutrinos and photons. The IceCube Collaboration has observed plenty of ultra-high energy neutrinos, including four events of PeV scale neutrinos. Recent studies suggested a possible energy dependent speed variation of GRB neutrinos in a similar way to that of GRB photons. Here we find that all four events of PeV neutrinos with associated GRB candidates can satisfy a regularity found from TeV neutrinos about a linear form correlation between the observed time difference and the LV factor. Such regularity indicates a Lorentz violation scale $E_{\rm LV}=(6.5\pm 0.4)\times10^{17}~{\rm GeV}$, which is comparable with that determined by GRB photons. We also suggest that neutrinos and anti-neutrinos can be superluminal and subluminal respectively due to opposite signs of LV correction.

  • A New Era in the Quest for Dark Matter

    by: Bertone, Gianfranco
    There is a growing sense of `crisis' in the dark matter community, due to the absence of evidence for the most popular candidates such as weakly interacting massive particles, axions, and sterile neutrinos, despite the enormous effort that has gone into searching for these particles. Here, we discuss what we have learned about the nature of dark matter from past experiments, and the implications for planned dark matter searches in the next decade. We argue that diversifying the experimental effort, incorporating astronomical surveys and gravitational wave observations, is our best hope to make progress on the dark matter problem.

  • $\Delta \left( 27\right)$ flavor singlet-triplet Higgs model for fermion masses and mixings

    by: Cárcamo Hernández, A.E. (Santa Maria U., Valparaiso) et al.

    We propose a multiscalar singlet extension of the singlet-triplet Higgs model consistent with the low energy fermion flavor data. Our model is based on the $\Delta \left( 27\right) $ family symmetry, which is supplemented with the $Z_{16}\times Z_{24}$ discrete group. The observed hierarchy of the SM charged fermion masses and quark mixing angles arises from the breaking of the $\Delta \left( 27\right) \times Z_{16}\times Z_{24}$ discrete group, whereas the light active neutrino masses are generated from a type-II seesaw mechanism mediated by the neutral component of the $SU(2)_{L}$ scalar triplet. The model symmetries lead to the extended Gatto-Sartori-Tonin relations between the quark masses and mixing angles.

  • Flavor Energy uncertainty relations for neutrino oscillations in quantum field theory

    by: Blasone, Massimo (Salerno U.) et al.

    In the context of quantum field theory, we derive flavor energy uncertainty relations for neutrino oscillations. By identifying the non conserved flavor charges with the clock observables, we arrive at the Mandelstam Tamm version of time energy uncertainty relations. In the ultrarelativistic limit these relations yield the well known condition for neutrino oscillations. Ensuing non relativistic corrections to the latter are explicitly evaluated. The analogy among flavor states and unstable particles and a novel interpretation of our uncertainty relations, based on the unitary inequivalence of Fock spaces for flavor and massive neutrinos, are also discussed.

  • Flavor of cosmic neutrinos preserved by ultralight dark matter

    by: Farzan, Yasaman (IPM, Tehran) et al.

    Within the standard propagation scenario, the flavor ratios of high-energy cosmic neutrinos at neutrino telescopes are expected to be around the democratic benchmark resulting from hadronic sources, $\left( 1 : 1 : 1 \right)_\oplus$. We show how the coupling of neutrinos to an ultralight dark matter complex scalar field would induce an effective neutrino mass that could lead to adiabatic neutrino propagation. This would result in the preservation at the detector of the production flavor composition of neutrinos at sources. This effect could lead to flavor ratios at detectors well outside the range predicted by the standard scenario of averaged oscillations. We also present an electroweak-invariant model that would lead to the required effective interaction between neutrinos and dark matter.

  • Exploring the ultra-light to sub-MeV dark matter window with atomic clocks and co-magnetometers

    by: Alonso, Rodrigo (CERN) et al.

    Particle dark matter could have a mass anywhere from that of ultralight candidates, $m_\chi\sim 10^{-21}\,$eV, to scales well above the GeV. Conventional laboratory searches are sensitive to a range of masses close to the weak scale, while new techniques are required to explore candidates outside this realm. In particular lighter candidates are difficult to detect due to their small momentum. Here we study two experimental set-ups which {\it do not require transfer of momentum} to detect dark matter: atomic clocks and co-magnetometers. These experiments probe dark matter that couples to the spin of matter via the very precise measurement of the energy difference between atomic states of different angular momenta. This coupling is possible (even natural) in most dark matter models, and we translate the current experimental sensitivity into implications for different dark matter models. It is found that the constraints from current atomic clocks and co-magnetometers can be competitive in the mass range $m_\chi\sim 10^{-21}-10^3\,$eV, depending on the model. We also comment on the (negligible) effect of different astrophysical neutrino backgrounds.

  • Unitarity Bounds of Astrophysical Neutrinos

    by: Ahlers, Markus (Bohr Inst.) et al.

    The flavor composition of astrophysical neutrinos observed at neutrino telescopes is related to the initial composition at their sources via oscillation-averaged flavor transitions. If the time evolution of the neutrino flavor states is unitary, the probability of neutrinos changing flavor is solely determined by the unitary mixing matrix that relates the neutrino flavor and propagation eigenstates. In this paper we derive general bounds on the flavor composition of TeV-PeV astrophysical neutrinos based on unitarity constraints. These bounds are useful for studying the flavor composition of high-energy neutrinos, where energy-dependent non-standard flavor mixing can dominate over the standard mixing observed in accelerator, reactor, and atmospheric neutrino oscillations.

  • MiniBooNE, MINOS+ and IceCube data imply a baroque neutrino sector

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

    The 4.8$\sigma$ anomaly in MiniBooNE data cannot be reconciled with MINOS+ and IceCube data within the vanilla framework of neutrino oscillations involving an eV-mass sterile neutrino. We show that a consistent picture can be drawn if charged-current and neutral-current nonstandard neutrino interactions are at work in the 3+1 neutrino scheme. It appears that either the neutrino sector is more elaborate than usually envisioned, or one or more datasets needs revision.

  • Higgs Criticality in a Viable Motivated Model

    by: Salvio, Alberto (CERN)

    An extension of the Standard Model with three right-handed neutrinos and a simple invisible axion model can account for all experimentally confirmed signals of new physics (neutrino oscillations, dark matter and baryon asymmetry) in addition to solving the strong CP problem, stabilizing the electroweak vacuum and satisfying all current observational bounds. We show that this model can also implement critical Higgs inflation, which corresponds to the frontier between stability and metastability of the electroweak vacuum. This leads to a value of the non-minimal coupling between the Higgs and the Ricci scalar that is much lower than the one usually quoted in Higgs inflation away from criticality. Then, an advantage is that the scale of perturbative unitarity breaking on flat spacetime can be very close to the Planck mass, where anyhow new physics is required. The higher dimensional operators are under control in this inflationary setup. The dependence of the cutoff on the Higgs background is also taken into account as appropriate when the Higgs is identified with the inflaton. Furthermore, critical Higgs inflation enjoys a robust inflationary attractor that makes it an appealing setup for the early universe. In the proposed model, unlike in the Standard Model, critical Higgs inflation can be realized without any tension with the observed quantities, such as the top mass and the strong coupling.

  • On the capture rates of big bang neutrinos by nuclei within the Dirac and Majorana hypotheses

    by: Roulet, Esteban (Centro Atomico Bariloche) et al.

    The capture rates of non-relativistic neutrinos on beta decaying nuclei depends on whether their mass is Dirac or Majorana. It is known that for relic neutrinos from the big-bang, and within minimal assumptions, the rate is a factor two larger in the Majorana case. We show that this difference also depends on the value of the lightest neutrino mass and on the type of mass hierarchy. If the lightest neutrino has a mass below the meV, so that it is still relativistic today, its capture rate for the case of Dirac masses becomes equal to that for Majorana masses. As a consequence, for the case of normal neutrino mass hierarchy, for which the total capture rate is dominated by the contribution from the lightest neutrino, if this one is below the meV the distinction between the Dirac and Majorana scenarios can only rely on the detection of the two heavier neutrinos, which is something very challenging.

  • On the scattering of a high-energy cosmic ray electrons off the dark matter

    by: Beylin, V. (Southern Federal U.) et al.

    High-energy cosmic ray electrons interaction with Dark Matter particles are considered. In particular, a weakening of energy spectrum of cosmic electrons is predicted resulting from inelastic electron scattering on hyper-pions in the hypercolor extension of the Standard Model. Corresponding cross section and angular distributions of secondary neutrino are calculated and studied. We also briefly discuss some effects of scattering processes of such type.

  • Detecting CP Violation in the Presence of Non-Standard Neutrino Interactions

    by: Hyde, Jeffrey M. (Johns Hopkins U.)

    New physics beyond the Standard Model could appear at long baseline oscillation experiments as non-standard interactions (NSI) between neutrinos and matter. If so, determination of the CP-violating phase $\delta_{13}$ is ambiguous due to interference with additional complex phases. I'll present my work using both numerical solutions and a perturbative approach to study oscillation probabilities in the presence of NSI. I'll show how the CP phase degeneracies are visualized on biprobability plots, and the extent to which the energy spectrum for a given baseline length can help resolve them. In particular, this shows how the broad range of energies at DUNE would help distinguish between maximal, standard CP violation and the absence of CP violation with large $\epsilon_{e\tau}$.

  • Constraining neutrino mass with tomographic weak lensing one-point probability distribution function and power spectrum

    by: Liu, Jia (Princeton U. (main)) et al.

    We study the constraints on neutrino mass sum (M_nu) from the one-point probability distribution function (PDF) and power spectrum of weak lensing measurements for an LSST-like survey, using the MassiveNuS simulations. The PDF provides access to non-Gaussian information beyond the power spectrum. It is particularly sensitive to nonlinear growth on small scales, where massive neutrinos also have the largest effect. We find that tomography helps improve the constraint on M_nu by 14% and 32% for the power spectrum and the PDF, respectively, compared to a single redshift bin. The PDF alone outperforms the power spectrum in constraining M_nu. When the two statistics are combined, the constraint is further tightened by 35%. We conclude that weak lensing PDF is complementary to the power spectrum and has the potential to become a powerful tool for constraining neutrino mass.

  • Effects of LESA in Three-Dimensional Supernova Simulations with Multi-Dimensional and Ray-by-Ray-plus Neutrino Transport

    by: Glas, Robert (Garching, Max Planck Inst.) et al.

    A set of eight self-consistent, time-dependent supernova (SN) simulations in three spatial dimensions (3D) for 9 solar-mass and 20 solar-mass progenitors is evaluated for the presence of dipolar asymmetries of the electron lepton-number emission as discovered by Tamborra et al. and termed lepton-number emission self-sustained asymmetry (LESA). The simulations were performed with the Aenus-Alcar neutrino/hydrodynamics code, which treats the energy- and velocity-dependent transport of neutrinos of all flavors by a two-moment scheme with algebraic M1 closure. For each of the progenitors, results with fully multi-dimensional (FMD) neutrino transport and with ray-by-ray-plus (RbR+) approximation are considered for two different grid resolutions. While the 9 solar-mass models develop explosions, the 20 solar-mass progenitor does not explode with the employed version of simplified neutrino opacities. In all 3D models we observe the growth of substantial dipole amplitudes of the lepton-number (electron neutrino minus antineutrino) flux with stable or slowly time-evolving direction and overall properties fully consistent with the LESA phenomenon. Models with RbR+ transport develop LESA dipoles somewhat faster and with temporarily higher amplitudes, but the FMD calculations exhibit cleaner hemispheric asymmetries with a far more dominant dipole. In contrast, the RbR+ results display much wider multipole spectra of the neutrino-emission anisotropies with significant power also in the quadrupole and higher-order modes. Our results disprove speculations that LESA is a numerical artifact of RbR+ transport. We also discuss LESA as consequence of a dipolar convection flow inside of the nascent neutron star and establish, tentatively, a connection to Chandrasekhar's linear theory of thermal instability in spherical shells.

  • Many-Body Neutrino-Exchange Interactions and Neutrino Mass: Comment on Phys. Rev. Lett. 120, 223202 (2018)

    by: Fischbach, E. (Purdue U.)

    This Comment corrects an erroneous remark by Stadnik in a recent paper to the effect that many-body neutrino-mediated forces are suppressed in all types of stars.

  • Induced resonance makes light sterile neutrino Dark Matter cool

    by: Bezrukov, F. (Manchester U.) et al.

    We describe two new generation mechanisms for Dark Matter composed of sterile neutrinos with $O(1)$ keV mass. The model contains a light scalar field which coherently oscillates in the early Universe and modulates the Majorana mass of the sterile neutrino. In a region of model parameter space, the oscillations between active and sterile neutrinos are resonantly enhanced. This mechanism allows us to produce sterile neutrino DM with small mixing angle with active neutrinos, thus evading the X-ray constraints. At the same time the spectrum of produced DM is much cooler, than in the case of ordinary oscillations in plasma, opening a window of lower mass DM, which is otherwise forbidden by structure formation considerations. In other regions of the model parameter space, where the resonance does not appear, another mechanism can operate: large field suppresses the active-sterile oscillations, but instead sterile neutrinos are produced by the oscillating scalar field when the effective fermion mass crosses zero. In this case DM component is cold, and even 1 keV neutrino is consistent with the cosmic structure formation.

  • Constraining high-energy neutrinos from choked-jet supernovae with IceCube high-energy starting events

    by: Esmaili, Arman
    Different types of core-collapse supernovae (SNe) have been considered as candidate sources of high-energy cosmic neutrinos. Stripped-envelope SNe, including energetic events like hypernovae and super-luminous SNe, are of particular interest. They may harbor relativistic jets, which are capable of explaining the diversity among gamma-ray bursts (GRBs), low-luminosity GRBs, ultra-long GRBs, and broadline Type Ib/c SNe. Using the six-year IceCube data on high-energy starting events (HESEs), we perform an unbinned maximum likelihood analysis to search for spatial and temporal coincidences with 222 samples of SNe Ib/c. We find that the present data are consistent with the background only hypothesis, by which we place new upper constraints on the isotropic-equivalent energy of cosmic rays, ${\mathcal E}_{\rm cr}\lesssim{10}^{52}~{\rm erg}$, in the limit that all SNe are accompanied by on-axis jets. Our results demonstrate that not only upgoing muon neutrinos but also HESE data enable us to constrain the potential contribution of these SNe to the diffuse neutrino flux observed in IceCube. We also discuss implications for the next-generation neutrino detectors such as IceCube-Gen2.

  • Majorons as cold light dark matter

    by: Heeck, Julian (Brussels U.)

    Majorons are the Goldstone bosons of spontaneously broken lepton number and hence intimately connected to Majorana neutrino masses. Since all majoron couplings are heavily suppressed by the seesaw scale they are interesting candidates for long-lived dark matter. The signature decay into two mono-energetic neutrinos is potentially detectable with neutrino detectors for majoron masses above MeV and complementary to the loop-induced decays into visible particles. The mass range between keV and MeV can only be probed indirectly with the majoron decay into two photons; keV-scale majorons can be warm or cold dark matter depending on the underlying freeze-in mechanism.

  • Impact of Matter Density Profile Shape on Non-Standard Interactions at DUNE

    by: Chatterjee, Animesh (Texas U., Arlington) et al.

    We discuss the impact of matter density profile shape on the determination of nonstandard neutrino matter interactions (NSI) in the context of the long baseline accelerator experiments such as Deep Underground Neutrino Experiment (DUNE). The primary scientific goals of DUNE are to determine the neutrino mass hierarchy, the leptonic CP violation phase, and the existence of new physics beyond the standard model of particles. Here we study the role of different earth matter density profiles on the question of observing standard oscillation as wells as NSI at DUNE. We consider two different earth matter density profiles which are relevant for the DUNE baseline. We first discuss the impact of matter on both appearance and disappearance oscillation channels, then we demonstrate the effect of different matter density profiles on the determination of NSI. We consider four different scenarios of NSI and elucidate the effect at the oscillation probability and measurement of number of events at DUNE. In one case of study we show that a nonstandard complex phase $\phi_{e\tau}$ could significantly increase the sensitivity to different matter distributions along the baseline.

  • Normal-mode Analysis for Collective Neutrino Oscillations

    by: Airen, Sagar (Indian Inst. Tech., Mumbai) et al.

    In an interacting neutrino gas, collective modes of flavor coherence emerge that can be propagating or unstable. We derive the general dispersion relation in the linear regime that depends on the neutrino energy and angle distribution. The essential scales are the vacuum oscillation frequency $\omega=\Delta m^2/(2E)$, the neutrino-neutrino interaction energy $\mu=\sqrt{2}G_{\rm F} n_\nu$, and the matter potential $\lambda=\sqrt{2}G_{\rm F} n_e$. Collective modes require non-vanishing $\mu$ and may be dynamical even for $\omega=0$ ('fast modes'), or they may require $\omega\not=0$ ('slow modes'). The growth rate of unstable fast modes can be fast itself (independent of $\omega$) or can be slow (suppressed by $\sqrt{|\omega/\mu|}$). We clarify the role of flavor mixing, which is ignored for the identification of collective modes, but necessary to trigger collective flavor motion. A large matter effect is needed to provide an approximate fixed point of flavor evolution, while spatial or temporal variations of matter and/or neutrinos are required as a trigger, i.e., to translate the disturbance provided by the mass term to seed stable or unstable flavor waves. We work out explicit examples to illustrate these points.

  • Low Scale Left-Right Symmetry and Naturally Small Neutrino Mass

    by: Brdar, Vedran (Heidelberg, Max Planck Inst.) et al.

    We consider the low scale ($10$ - $100$ TeV) left-right symmetric model with "naturally" small neutrino masses generated through the inverse seesaw mechanism. The Dirac neutrino mass terms are taken to be similar to the masses of charged leptons and quarks in order to satisfy the quark-lepton similarity condition. The inverse seesaw implies the existence of fermion singlets $S$ with Majorana mass terms as well as the "left" and "right" Higgs doublets. These doublets provide the portal for $S$ and break the left-right symmetry. The inverse seesaw allows to realize a scenario in which the large lepton mixing originates from the Majorana mass matrix of $S$ fields which has certain symmetry. The model contains heavy pseudo-Dirac fermions, formed by $S$ and the right-handed neutrinos, which have masses in the $1$ GeV - $100$ TeV range and can be searched for at current and future colliders such as LHC and FCC-ee as well as in SHiP and DUNE experiments. Their contribution to neutrinoless double beta decay is unobservable. The radiative corrections to the mass of the Higgs boson and the possibility for generating the baryon asymmetry of the Universe are discussed. Modification of the model with two singlets ($S_L$ and $S_R$) per generation can provide a viable keV-scale dark matter candidate.

  • Late time supernova neutrino signal and proto-neutron star radius

    by: Gallo Rosso, A. (GSSI, Aquila) et al.

    We discuss the possibility of reconstructing the newly formed proto-neutron star radius from the late time neutrino signal. A black-body emission is assumed for the neutron star cooling phase. We parametrize the neutrino time-integrated fluxes based on simulations of Roberts and Reddy. A likelihood analysis of the inverse-beta decay and elastic scattering events in Hyper-Kamiokande is performed in both three flavor and an effective one flavor scenario. We show that the precision achievable in the radius reconstruction strongly depends on a correlation with the pinching parameter and therefore the corresponding prior. Although this correlation hinders the precise measurement of the newly formed neutron star radius, it could help measure the pinching parameters with good accuracy in view of the current constraints on neutron star radius, or if the neutron star radius is precisely measured.

  • A Novel Approach to Neutrino-Hydrogen Measurements

    by: Duyang, H. (South Carolina U.) et al.

    The lack of high statistics samples of (anti)neutrino-hydrogen interactions has been a longstanding impediment for neutrino physics. We propose a practical way to achieve accurate (anti)neutrino-hydrogen measurements, solving some of the principal limitations of neutrino experiments. Interactions on hydrogen are extracted by subtracting measurements on a dedicated graphite (pure C) target from those on a dedicated polypropylene (CH$_2$) target within a highly segmented detector. A statistics of ${\cal O}(10^6)$ can be realistically achieved for the various $\nu(\bar \nu)$-H event topologies, with efficiencies exceeding 90\% and purities around 80-92\%. The availability of such samples allows a determination of neutrino and antineutrino fluxes with unprecedented precision, as well as, by contrasting these samples to corresponding measurements on heavy materials, a measurement of initial and final state nuclear effects. The systematic uncertainties associated with both the fluxes and the nuclear smearing are crucial for modern long-baseline neutrino oscillation experiments. (Anti)neutrino-hydrogen interactions also provide an ideal tool for a wide range of precision tests of fundamental interactions.

  • Leptogenesis from Low Energy $CP$ Violation
    SISSA 38/2018/FISI

    by: Moffat, K. (Durham U., IPPP) et al.

    We revisit the possibility of producing the observed baryon asymmetry of the Universe via thermal leptogenesis, where $CP$ violation comes exclusively from the low-energy phases of the neutrino mixing matrix. We demonstrate the viability of thermal leptogenesis across seven orders of magnitude $\left(10^{6}

  • Charged-current scattering off $^{16}$O nucleus as a detection channel for supernova neutrinos

    by: Nakazato, Ken'ichiro
    Event spectra of the neutrino-$^{16}$O charged-current reactions in Super-Kamiokande are evaluated for a future supernova neutrino burst. Since these channels are expected to be useful for diagnosing a neutrino spectrum with high average energy, the evaluations are performed not only for an ordinary supernova neutrino model but also for a model of neutrino emission from a black-hole-forming collpase. Using shell model results, whose excitation energies are consistent with the experimental data, the cross sections of the $^{16}$O($\nu_e, e^-$)X and $^{16}$O($\bar\nu_e, e^+$)X reactions for each nuclear state with a different excitation energy are employed in this study. It is found that, owing to the components of the reaction with higher excitation energy, the event spectrum becomes 4-7 MeV softer than that in the case without considering the excitation energies. In addition, a simplified approach to evaluate the event spectra is proposed for convenience and its validity is examined.

  • Highly-boosted dark matter and cutoff for cosmic-ray neutrino through neutrino portal

    by: Yin, Wen (Beijing, Inst. High Energy Phys.)

    We study the cutoff for the cosmic-ray neutrino, set by the scattering with cosmic background neutrinos into dark sector particles through a neutrino portal interaction. We find that a large interaction rate is still viable, when the dark sector particles are mainly coupled to the ${\tau}$-neutrino, so that the neutrino mean free path can be reduced to be O(10) Mpc over a wide energy range. If stable enough, the dark sector particle, into whom most of the cosmic-ray neutrino energy is transferred, can travel across the Universe and reach to the earth. The energy of them can be as large as O(EeV) if originates from a cosmogenic neutrino.

  • Model-Independent Bounds on $R(J/\psi)$ via Dispersive Relations

    by: Lamm, Henry (Maryland U.)

    Model-independent bounds on $R(J/\psi) \! \equiv \!\mathcal{BR} (B_c^+ \rightarrow J/\psi \, \tau^+\nu_\tau)/$ $\mathcal{BR} (B_c^+ \rightarrow J/\psi \, \mu^+\nu_\mu)$ are obtained through a combination of dispersive relations, heavy-quark relations at zero-recoil, and the limited existing form factor determinations from lattice QCD. The resulting 95% confidence-level bound, $0.20\leq R(J/\psi)\leq0.39$, agrees with the recent LHCb result at $1.3 \, \sigma$, and removes the dominant model-dependent uncertainty from theory predictions. Using the same techniques, a prediction of $R(\eta_c)=0.29(5)$ is obtained.

  • The Lyman-$\alpha$ forest as a diagnostic of the nature of the dark matter

    by: Garzilli, Antonella (Bohr Inst.) et al.

    The observed Lyman-$\alpha$ flux power spectrum (FPS) is suppressed on scales below $\sim~ 30~{\rm km~s}^{-1}$. This cutoff could be due to the high temperature, $T_0$, and pressure, $p_0$, of the absorbing gas or, alternatively, it could reflect the free streaming of dark matter particles in the early universe. We perform a set of very high resolution cosmological hydrodynamic simulations in which we vary $T_0$, $p_0$ and the amplitude of the dark matter free streaming, and compare the FPS of mock spectra to the data. We show that the location of the dark matter free-streaming cutoff scales differently with redshift than the cutoff produced by thermal effects and is more pronounced at higher redshift. We, therefore, focus on a comparison to the observed FPS at $z>5$. We demonstrate that the FPS cutoff can be fit assuming cold dark matter, but it can be equally well fit assuming that the dark matter consists of $\sim 7$ keV sterile neutrinos in which case the cutoff is due primarily to the dark matter free streaming.

  • Symmetries and Algebraic Methods in Neutrino Physics
    J.Phys. G45 (2018) 113001

    by: Balantekin, A.B.
    Symmetry properties associated with neutrino propagation with or without a background of other particles, including neutrinos, is reviewed. The utility of symmetries is illustrated with examples chosen from the see-saw mechanism and both matter-enhanced and collective neutrino oscillations. The role of symmetries in neutrino astrophysics is highlighted.

  • Matter Effect of Light Sterile Neutrino: An Exact Analytical Approach
    JHEP 1810 (2018) 021

    by: Li, Wei (Jinan U.) et al.

    The light sterile neutrino, if it exists, will give additional contribution to matter effect when active neutrinos propagate through terrestrial matter. In the simplest 3+1 scheme, three more rotation angles and two more CP-violating phases in lepton mixing matrix make the interaction complicated formally. In this work, the exact analytical expressions for active neutrino oscillation probabilities in terrestrial matter, including sterile neutrino contribution, are derived. It is pointed out that this set of formulas contain information both in matter and in vacuum, and can be easily tuned by choosing related parameters. Based on the generic exact formulas, we present oscillation probabilities of typic medium and long baseline experiments. Taking NOνA experiment as an example, we show that in particular parameter space sterile neutrino gives important contribution to terrestrial matter effect, and Dirac phases play a vital role.

  • Impact of vector new physics couplings on $B_s \to (K,\,K^{\ast})\tau\nu$ and $B \to \pi\tau\nu$ decays
    Phys.Rev. D98 (2018) 055024

    by: Rajeev, N. (NIT, Silchar) et al.

    Experimental measurements of $R_{D}$, $R_{D^*}$ and $R_{J/\Psi}$ in $B \to (D,\,D^{\ast})l\nu$ and $B_c \to J/\Psi l \nu$ decays mediated via $b \to c\,l\,\nu$ charged current interactions deviate from standard model prediction by $2.3\sigma$, $3.4\sigma$ and $2\sigma$, respectively. In addition, a deviation of $1.5\sigma$ from the standard model prediction has been witnessed in $\mathcal B(B \to \tau \nu)$ mediated via $b \to u\,l\,\nu$ charged current interactions as well. Motivated by the anomalies present in $B$ and $B_c$ meson decays, we analyze the corresponding $B_s \to (K,\,K^{\ast})\,\tau\,\nu$ and $B \to \pi\tau\nu$ semileptonic decays within the standard model and beyond. We use an effective field theory formalism in which $b \to c$ and $b \to u$ semileptonic decays are assumed to exhibit similar new physics patterns. We give the predictions of various observables such as the branching fractions, ratio of branching ratios, lepton side forward backward asymmetry, lepton polarization fraction and convexity parameter for $B_s \to (K,\,K^{\ast})\tau \nu$ and $B \to \pi\tau\nu$ decay channels within the standard model and within various NP scenarios.

  • Thermal production of light Dirac right-handed sneutrino dark matter
    Phys.Dark Univ. 22 (2018) 96-100

    by: Choi, Ki-Young (Sungkyunkwan U.) et al.

    We consider the production of right-handed (RH) sneutrino dark matter in a model of Dirac neutrino where neutrino Yukawa coupling constants are very small. Dark matter RH sneutrinos are produced by scatterings and decays of thermal particles in the early Universe without reaching thermal equilibrium due to the small Yukawa couplings. We show that not only decays of thermal particles but also the thermal scatterings can be a dominant source as well as non-thermal production in a scenario with light sneutrinos and charged sleptons while other supersymmetric particles are heavy. We also discuss the cosmological implications of this scenario.

  • Charge Quantization and Neutrino Mass from Planck-scale SUSY
    Phys.Lett. B785 (2018) 585-590

    by: Yin, Wen (Beijing, Inst. High Energy Phys.)

    We show a possibility for the charge quantization of the standard model (SM) particles. If a global symmetry makes the three copies of a generation and supersymmetry (SUSY) relates the Higgs boson to a lepton, all the charges of the SM particles can be quantized through gauge-anomaly cancellation. In the minimal model realizing the possibility, the gravitino mass around the Planck-scale is needed to generate the SM couplings through (quantum) supergravity. Much below the Planck-scale, the SM is obtained as the effective theory. Interestingly, if the gaugino masses are generated through anomaly mediation, one of the neutrino masses is predicted to be around the neutrino oscillation scales. In an extension of the model, millicharged particles can exist without introducing massless hidden photons.

  • Angular distributions in electroweak pion production off nucleons: odd parity hadron terms, strong relative phases and model dependence
    Phys.Rev. D98 (2018) 073001

    by: Sobczyk, J. E. (Valencia U., IFIC) et al.

    The study of pion production in nuclei is important for signal and background determinations in current and future neutrino oscillation experiments. The first step, however, is to understand the pion production reactions at the free nucleon level. We present an exhaustive study of the charged-current and neutral-current neutrino and antineutrino pion production off nucleons, paying special attention to the angular distributions of the outgoing pion. We show, using general arguments, that parity violation and time-reversal odd correlations in the weak differential cross sections are generated from the interference between different contributions to the hadronic current that are not relatively real. Next, we present a detailed comparison of three state-of-the-art, microscopic models for electroweak pion production off nucleons, and we also confront their predictions with polarized electron data, as a test of the vector content of these models. We also illustrate the importance of carrying out a comprehensive test at the level of outgoing pion angular distributions, going beyond comparisons done for partially integrated cross sections, where model differences cancel to a certain extent. Finally, we observe that all charged and neutral current distributions show sizable anisotropies, and identify channels for which parity-violating effects are clearly visible. Based on the above results, we conclude that the use of isotropic distributions for the pions in the center of mass of the final pion-nucleon system, as assumed by some of the Monte Carlo event generators, needs to be improved by incorporating the findings of microscopic calculations.

  • Neutrino masses and gauged $U(1)_\ell$ lepton number
    JHEP 1810 (2018) 015

    by: Chang, We-Fu (Taiwan, Natl. Tsing Hua U.) et al.

    We investigate the tree-level neutrino mass generation in the gauged $U(1)_\ell$ lepton model recently proposed by us [arXiv:1805.10382]. With the addition of one Standard Model(SM) singlet, $\phi_1(Y=0, \ell=1)$, and one SM triplet scalar, $T(Y=-1,\ell=0)$, realistic lepton masses can be accommodated. The resulting magnitude of neutrino mass is given by $\sim v_t^3/v_L^2$, where $v_t$ and $v_L$ are the vacuum expectation values of $T$ and $\phi_1$, respectively, and it is automatically of the inverse see-saw type. Since $v_L$ is the lepton number violation scale we take it to be high, i.e. ${\cal O} \gtrsim (\mbox{TeV})$. Moreover, the induced lepton flavor violating processes and the phenomenology of the peculiar triplet are studied. An interesting bound, $0.1\lesssim v_t\lesssim24.1$ GeV, is obtained when taking into account the neutrino mass generation, $Br(\mu\rightarrow e \gamma)$, and the limits from oblique parameters, $\Delta S$ and $\Delta T$. Collider phenomenology of the SM triplets is also discussed.

  • $ {R}_{D^{\left(*\right)}},{R}_{K^{\left(*\right)}} $ and neutrino mass in the 2HDM-III with right-handed neutrinos
    JHEP 1809 (2018) 149

    by: Li, Shao-Ping (CCNU, Wuhan, Inst. Part. Phys.) et al.

    Given that the two-Higgs-doublet model of type III (2HDM-III) has the potential to address the $ {R}_{D^{\left(*\right)}} $ anomalies while the resolution to the $ {R}_{K^{\left(*\right)}} $ deficits requires new degrees of freedom within this framework, we consider in this paper a unified scenario where the low-scale type-I seesaw mechanism is embedded into the 2HDM-III, so as to accommodate the $ {R}_{D^{\left(*\right)}} $ and $ {R}_{K^{\left(*\right)}} $ anomalies as well as the neutrino mass. We first revisit the $ {R}_{D^{\left(*\right)}} $ anomalies and find that the current world-averaged results can be addressed at 2σ level without violating the bound from the branching ratio $ \mathrm{\mathcal{B}}\left({B}_c^{-}\to {\tau}^{-}\overline{\nu}\right) $ ≤ 30%. The scenario predicts two sub-eV neutrino masses based on a decoupled heavy Majorana neutrino and two nearly degenerate Majorana neutrinos with mass around the electroweak scale. For the $ {R}_{K^{\left(*\right)}} $ anomalies, the same scenario can generate the required Wilson coefficients in the direction C$_{9 μ}^{NP}$  = − C$_{10 μ}^{NP}$  < 0, with $ \mathcal{O}(1) $ Yukawa couplings for the muon and the top quark.

  • Blazar Flares as an Origin of High-Energy Cosmic Neutrinos?
    Astrophys.J. 865 (2018) 124

    by: Murase, Kohta (Penn State U., University Park (main)) et al.

    We consider implications of high-energy neutrino emission from blazar flares, including the recent event IceCube-170922A and the 2014–2015 neutrino flare that could originate from TXS 0506+056. First, we discuss their contribution to the diffuse neutrino intensity taking into account various observational constraints. Blazars are likely to be subdominant in the diffuse neutrino intensity at sub-PeV energies, and we show that blazar flares like those of TXS 0506+056 could make ≲1%–10% of the total neutrino intensity. We also argue that the neutrino output of blazars can be dominated by the flares in the standard leptonic scenario for their γ-ray emission, and energetic flares may still be detected with a rate of . Second, we consider multi-messenger constraints on the source modeling. We show that luminous neutrino flares should be accompanied by luminous broadband cascade emission, emerging also in X-rays and γ-rays. This implies that not only γ-ray telescopes like Fermi but also X-ray sky monitors such as Swift and MAXI are critical to test the canonical picture based on the single-zone modeling. We also suggest a two-zone model that can naturally satisfy the X-ray constraints while explaining the flaring neutrinos via either photomeson or hadronuclear processes.

  • The Bearable Compositeness of Leptons
    JHEP 1810 (2018) 017

    by: Frigerio, Michele (U. Montpellier, L2C) et al.

    Partial compositeness as a theory of flavor in the lepton sector is assessed. We begin presenting the first systematic analysis of neutrino mass generation in this context, and identifying the distinctive mass textures. We then update the bounds from charged lepton flavor and CP violating observables. We put forward a $U(1)^3\times CP$ symmetry of the composite sector, in order to allow the new physics to be not far above the TeV scale. This hypothesis effectively suppresses the new contributions to the electron EDM and $\mu\to e\gamma$, by far the most constraining observables, and results in a novel pattern of flavor violation and neutrino masses. The CP violation in the elementary-composite mixing is shown to induce a CKM phase of the correct size, as well as order-one phases in the PMNS matrix. We compare with the alternative possibility of introducing multiple scales of compositeness for leptons, that also allow to evade flavor and CP constraints. Finally, we examine violations of lepton flavor universality in $B$-meson semi-leptonic decays. The neutral-current anomalies can be accommodated, predicting strong correlations among different lepton flavors, with a few channels close to the experimental sensitivity.

  • Flavored non-minimal left–right symmetric model fermion masses and mixings
    Eur.Phys.J. C78 (2018) 812

    by: Garcés, E.A. (CINVESTAV, IPN) et al.

    A complete study on the fermion masses and flavor mixing is presented in a non-minimal left-right symmetric model (NMLRMS) where the ${\bf S}_{3}\otimes {\bf Z}_{2}\otimes {\bf Z}^{e}_{2}$ flavor symmetry drives the Yukawa couplings. In the quark sector, the mass matrices possess a kind of the generalized Fritzsch textures that allow us to fit the CKM mixing matrix in good agreement to the last experimental data. In the lepton sector, on the other hand, a soft breaking of the $\mu\leftrightarrow \tau$ symmetry provides a non zero and non maximal reactor and atmospheric angles, respectively. The inverted and degenerate hierarchy are favored in the model where a set of free parameters is found to be consistent with the current neutrino data.

  • Model-independent bounds on $R(J/\psi)$
    JHEP 1809 (2018) 168

    by: Cohen, Thomas D. (Maryland U.) et al.

    We present a model-independent bound on $ R\left(J/\psi \right)\equiv \mathrm{\mathcal{B}}\mathrm{\mathcal{R}}\left({B}_C^{+}\to J/\psi {\tau}^{+}{\nu}_{\tau}\right)/\mathrm{\mathcal{B}}\mathrm{\mathcal{R}}\left({B}_C^{+}\to J/\psi {\mu}^{+}{\nu}_{\mu}\right) $ . This bound is constructed by constraining the form factors through a combination of dispersive relations, heavy-quark relations at zero-recoil, and the limited existing determinations from lattice QCD. The resulting 95% confidence-level bound, 0.20 ≤ R(J/ψ) ≤ 0.39, agrees with the recent LHCb result at 1.3σ, and rules out some previously suggested model form factors.

  • Revisiting $B \to \pi\pi \ell \nu$ at large dipion masses
    JHEP 1810 (2018) 030

    by: Feldmann, Thorsten (Siegen U.) et al.

    We revisit QCD factorization of $B\to \pi\pi$ form factors at large dipion masses, by deriving new constraints based on the analyticity properties of these objects. We then propose a parametrization of the form factors, inspired by the leading-twist QCD factorization formula, that incorporates all known analytic properties. This parameterization is used to interpolate between the QCDF results and the constraints from the $B^*$ pole. Based on this interpolation, we predict the $B\to \pi\pi\ell\nu$ decay rate in a larger phase space region than previous studies could. We obtain a partially-integrated branching ratio up to $\mathcal{B} \simeq \mathcal{O}({10^{-6}})$, which implies that a measurement of the non-resonant semileptonic decay is potentially within reach of the Belle II experiment.

  • One-loop effective LFV $\varvec{Zl_kl_m}$ vertex from heavy neutrinos within the mass insertion approximation
    Eur.Phys.J. C78 (2018) 815

    by: Herrero, M.J. (Madrid, Autonoma U.) et al.

    In this paper we study the effective lepton flavor violating vertex of an electroweak $Z$ gauge boson and two charged leptons with different flavor, $l_k$ and $l_m$, that is generated to one-loop in low scale seesaw models with right handed neutrinos whose masses are heavier than the electroweak scale. We first compute the form factor describing this vertex by using the mass insertion approximation, where the flavor non-diagonal entries of the neutrino Yukawa coupling matrix are the unique origin, to one-loop level, of lepton flavor changing processes with charged leptons in the external legs. Then, by considering the proper large right handed neutrino mass expansion of the form factor, we derive a formula for the $Z l_k l_m$ effective vertex which is very simple and useful for fast phenomenological estimates. In the last part of this work we focus on the phenomenological applications of this vertex for simple and accurate estimates of the $Z \to l_k {\bar l}_m$ decay rates. Concretely, this vertex will allow us to conclude easily on the maximum allowed decay rates by present data in the inverse seesaw model. The found rates are promising, at the reach of future lepton colliders.

  • Model-independent diagnostic of self-induced spectral equalization versus ordinary matter effects in supernova neutrinos
    Phys.Rev. D98 (2018) 063013

    by: Capozzi, Francesco (Munich, Max Planck Inst.) et al.

    Self-induced flavor conversions near the supernova (SN) core can make the fluxes for different neutrino species become almost equal, potentially altering the dynamics of the SN explosion and washing out all further neutrino oscillation effects. We present a new model-independent analysis strategy for the next galactic SN signal that will distinguish this flavor equalization scenario from a matter effects only scenario during the SN accretion phase. Our method does not rely on fitting or modelling the energy-dependent fluences of the different species to a known function, but rather uses a model-independent comparison of charged-current and neutral-current events at large next-generation underground detectors. Specifically, we advocate that the events due to elastic scattering on protons in a scintillator detector, which is insensitive to oscillation effects and can be used as a model-independent normalization, should be compared with the events due to inverse beta decay of $\bar\nu_e$ in a water Cherenkov detector and/or the events due to charged-current interactions of $\nu_e$ in an Argon detector. The ratio of events in these different detection channels allow one to distinguish a complete flavor equalization from a pure matter effect, for either of the neutrino mass orderings, as long as the spectral differences among the different species are not too small.

  • Probing the seesaw scale with gravitational waves
    Phys.Rev. D98 (2018) 063532

    by: Okada, Nobuchika (Alabama U.) et al.

    The $U(1)_{B-L}$ gauge symmetry is a promising extension of the standard model of particle physics, which is supposed to be broken at some high energy scale. Associated with the $U(1)_{B-L}$ gauge symmetry breaking, right-handed neutrinos acquire their Majorana masses and then tiny light neutrino masses are generated through the seesaw mechanism. In this paper, we demonstrate that the first-order phase transition of the $U(1)_{B-L}$ gauge symmetry breaking can generate a large amplitude of stochastic gravitational wave (GW) radiation for some parameter space of the model, which is detectable in future experiments. Therefore, the detection of GWs is an interesting strategy to probe the seesaw scale which can be much higher than the energy scale of collider experiments.

  • Mu-tau symmetry and the Littlest Seesaw
    Phys.Lett. B785 (2018) 391-398

    by: King, Stephen F. (Southampton U.) et al.

    Motivated by the latest neutrino oscillation data which is consistent with maximal atmospheric mixing and maximal leptonic CP violation, we review various results in μτ symmetry, then include several new observations and clarifications, including identifying a new general form of neutrino mass matrix with μτ symmetry. We then apply the new results to the neutrino mass matrix associated with the Littlest Seesaw model, and show that it approximately satisfies the new general form with μτ symmetry, and that this is responsible for its approximate predictions of maximal atmospheric mixing and maximal CP violation in the lepton sector.

  • Coherent scattering and macroscopic coherence: Implications for neutrino, dark matter and axion detection
    JHEP 1810 (2018) 045

    by: Akhmedov, Evgeny (Heidelberg, Max Planck Inst.) et al.

    We study the question of whether coherent neutrino scattering can occur on macroscopic scales, leading to a significant increase of the detection cross section. We concentrate on radiative neutrino scattering on atomic electrons (or on free electrons in a conductor). Such processes can be coherent provided that the net electron recoil momentum, i.e. the momentum transfer from the neutrino minus the momentum of the emitted photon, is sufficiently small. The radiative processes is an attractive possibility as the energy of the emitted photons can be as large as the momentum transfer to the electron system and therefore the problem of detecting extremely low energy recoils can be avoided. The requirement of macroscopic coherence severely constrains the phase space available for the scattered particle and the emitted photon. We show that in the case of the scattering mediated by the usual weak neutral current and charged current interactions this leads to a strong suppression of the elementary cross sections and therefore the requirement of macroscopic coherence results in a reduction rather than an increase of the total detection cross section. However, for the $\nu e$ scattering mediated by neutrino magnetic or electric dipole moments coherence effects can actually increase the detection rates. Effects of macroscopic coherence can also allow detection of neutrinos in 100 eV -- a few keV energy range, which is currently not accessible to the experiment. A similar coherent enhancement mechanism can work for relativistic particles in the dark sector, but not for the conventionally considered non-relativistic dark matter.

  • The Fundamental Need for a SM Higgs and the Weak Gravity Conjecture
    Phys.Lett. B786 (2018) 272-277

    by: Gonzalo, Eduardo (Madrid, IFT) et al.

    Compactifying the SM down to 3D or 2D one may obtain AdS vacua depending on the neutrino mass spectrum. It has been recently shown that, by insisting in the absence of these vacua, as suggested by {\it Weak Gravity Conjecture} (WGC) arguments, intriguing constraints on the value of the lightest neutrino mass and the 4D cosmological constant are obtained. For fixed Yukawa coupling one also obtains an upper bound on the EW scale $\left\langle H\right\rangle\lesssim {\Lambda_4^{1/4}} /{Y_{\nu_{i}}}$,where $\Lambda_4$ is the 4D cosmological constant and $Y_{\nu_{i}}$ the Yukawa coupling of the lightest (Dirac) neutrino. This bound may lead to a reassessment of the gauge hierarchy problem. In this letter, following the same line of arguments, we point out that the SM without a Higgs field would be inconsistent with a quantum gravity embedding, giving a fundamental basis for the very existence of the SM Higgs. Furthermore one can derive a lower bound on the Higgs vev $\left\langle H\right\rangle\gtrsim \Lambda_{\text{QCD}}$ which is required by the absence of AdS vacua in lower dimensions. This would explain the relative proximity of the EW and hadronic scales in the SM. The lowest number of quark/lepton generations in which this need for a Higgs applies is three, giving a justification for family replication. We also reassess the connection between the EW scale, neutrino masses and the c.c. in this approach. The EW fine-tuning is here related to the proximity between the c.c. scale $\Lambda_4^{1/4}$ and the lightest neutrino mass $m_{\nu_i}$ by the expression $ \frac {\Delta H}{H} \lesssim \frac {(a\Lambda_4^ {1/4} -m_{\nu_i})} {m_{\nu_i}}. $

  • On Neutrino Mixing in Matter and CP and T Violation Effects in Neutrino Oscillations
    SISSA 23/2018/FISI
    Phys.Lett. B785 (2018) 95-104

    by: Petcov, S.T. (INFN, Trieste) et al.

    Aspects of 3-neutrino mixing and oscillations in vacuum and in matter with constant density are investigated working with a real form of the neutrino Hamiltonian. We find the (approximate) equalities θ23m=θ23 and δm=δ , θ23 ( θ23m ) and δ ( δm ) being respectively the atmospheric neutrino mixing angle and the Dirac CP violation phase in vacuum (in matter) of the neutrino mixing matrix, which are shown to represent excellent approximations for the conditions of the T2K (T2HK), T2HKK, NO ν A and DUNE neutrino oscillation experiments. A new derivation of the known relation sin⁡2θ23msin⁡δm=sin⁡2θ23sin⁡δ is presented and it is used to obtain a correlation between the shifts of θ23 and δ due to the matter effect. A derivation of the relation between the rephasing invariants which determine the magnitude of CP and T violating effects in 3-flavour neutrino oscillations in vacuum, JCP , and of the T violating effects in matter with constant density, JTm≡Jm , reported in [1] without a proof, is presented. It is shown that the function F which appears in this relation, Jm=JCPF , and whose explicit form was given in [1] , coincides with the function F˜ in the similar relation Jm=JCPF˜ derived in [2] , although F and F˜ are expressed in terms of different sets of neutrino mass and mixing parameters and have completely different forms.

  • Weak pion production off the nucleon in covariant chiral perturbation theory
    Phys.Rev. D98 (2018) 076004

    by: Yao, De-Liang (Valencia U.) et al.

    Weak pion production off the nucleon at low energies has been systematically investigated in manifestly relativistic baryon chiral perturbation theory with explicit inclusion of the $\Delta$(1232) resonance. Most of the involved low-energy constants have been previously determined in other processes such as pion-nucleon elastic scattering and electromagnetic pion production off the nucleon. For numerical estimates, the few remaining constants are set to be of natural size. As a result, the total cross sections for single pion production on neutrons and protons, induced either by neutrino or antineutrino, are predicted. Our results are consistent with the scarce existing experimental data except in the $\nu_\mu n\to \mu^-n\pi^+$ channel, where higher-order contributions might still be significant. The $\Delta$ resonance mechanisms lead to sizeable contributions in all channels, especially in $\nu_\mu p\to \mu^- p\pi^+$, even though the considered energies are close to the production threshold. The present study provides a well founded low-energy benchmark for phenomenological models aimed at the description of weak pion production processes in the broad kinematic range of interest for current and future neutrino-oscillation experiments.

  • Coherency and incoherency in neutrino-nucleus elastic and inelastic scattering
    Phys.Rev. D98 (2018) 053004

    by: Bednyakov, Vadim A. (Dubna, JINR) et al.

    Neutrino-nucleus scattering $\nu A\to \nu A$, in which the nucleus conserves its integrity, is considered. We show that elastic interactions keeping the nucleus in the same quantum state lead to a quadratic enhancement of the corresponding cross-section in terms of the number of nucleons. Meanwhile, the cross-section of inelastic processes in which the quantum state of the nucleus is changed, essentially has a linear dependence on the number of nucleons. These two classes of processes are referred to as coherent and incoherent, respectively. The coherent and incoherent cross-sections are driven by factors $|F_{p/n}|^2$ and $(1-|F_{p/n}|^2)$, where $|F_{p/n}|^2$ is a proton/neutron form-factor of the nucleus, averaged over its initial states. The coherent cross-section formula used in the literature is revised and corrections depending on kinematics are estimated. As an illustration of the importance of the incoherent channel we considered three experimental setups with different nuclei. Experiments attempting to measure coherent neutrino scattering by solely detecting the recoiling nucleus, as is typical, might be including an incoherent background that is indistinguishable from the signal if the excitation gamma eludes its detection. However, as is shown here, the incoherent component can be measured directly by searching for photons released by the excited nuclei inherent to the incoherent channel. For a beam experiment these gammas should be correlated in time with the beam, and their higher energies make the corresponding signal easily detectable at a rate governed by the ratio of incoherent to coherent cross-sections. The detection of signals due to the nuclear recoil and excitation gammas provides a more sensitive instrument in studies of nuclear structure and possible signs of new physics.

  • Neutrino phenomenology from leptogenesis
    Eur.Phys.J. C78 (2018) 817

    by: Buccella, Franco (INFN, Naples) et al.

    Assuming a type-I seesaw mechanism for neutrino mass generation and invoking a baryogengesis via leptogenesis scenario, we consider a reasonable hierarchical structure for Dirac neutrino mass matrix, similar to up-type quark mass matrix. These hypotheses imply a relevant connection between high scale CP violation and low energy one. By requiring a compact heavy neutrino mass spectrum, which allows to circumvent Davidson-Ibarra limit, one can obtain an efficient leptogenesis restricting the allowed region for low energy neutrino parameters. Once the oscillating parameters are taken inside a $3\sigma$ range, through the numerical resolution of the leptogenesis Boltzmann equations one gets the following allowed intervals for the lightest neutrino mass and the Dirac CP phase: $-0.90\pi<\delta<-0.75\pi$ and $m_1\sim( 0.002 - 0.004)$ eV.

  • Scientific Works of Shoichi Sakata and Commentaries

    by: Maskawa, Toshihide (Nagoya U.)

  • Lepton Flavor Violating Dilepton Dijet Signatures from Sterile Neutrinos at Proton Colliders
    DESY 17-151
    JHEP 1810 (2018) 067

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

    In this article we investigate the prospects of searching for sterile neutrinos in lowscale seesaw scenarios via the lepton flavour violating (but lepton number conserving) dilepton dijet signature. In our study, we focus on the final state $e^\pm \mu^\mp jj$ at the HL-LHC and the FCC-hh (or the SppC). We perform a multivariate analysis at the detector level including the dominant SM backgrounds from di-top, di-boson, and tri-boson. Under the assumption of the active-sterile neutrino mixings $|V_{ l N}|^2=|\theta_e|^2=|\theta_\mu|^2$ and $|V_{ \tau N}|^2 = |\theta_\tau|^2=0$, the sensitivities on the signal production cross section times branching ratio $\sigma(p p \to l^\pm N)\times {\rm BR} (N \to l^{ \mp} jj)$ and on $|V_{ l N}|^2$ for sterile neutrino mass $M_N$ between 200 and 1000 GeV are derived. For the benchmark $M_N=500$ GeV, when ignoring systematic uncertainties at the HL-LHC (FCC-hh/SppC) with 3 (20) ${\rm ab}^{-1}$ luminosity, the resulting 2-$\sigma$ limits on $|V_{ l N}|^2$ are $4.9\times 10^{-3}$ ($7.0\times 10^{-5}$), while the 2 -$\sigma$ limit on $\sigma \times {\rm BR}$ are $4.4\times10^{-2}$ ($1.6\times10^{-2}$) fb, respectively. The effect of the systematic uncertainty is also studied and found to be important for sterile neutrinos with smaller masses. We also comment on searches with $\tau^\pm \mu^\mp jj$ and $\tau^\pm e^\mp jj$ final states.

  • Asymmetric tribimaximal texture
    Phys.Rev. D98 (2018) 055030

    by: Rahat, Moinul Hossain (Florida U.) et al.

    We construct a texture where the seesaw matrix is diagonalized by the tribimaximal (TBM) matrix with a phase. All angles of the Cabibbo-Kobayashi-Maskawa matrix and Pontecorvo-Maki-Nakagawa-Sakata matrix are consistent with particle data group values, and the mass relations of quarks and charged leptons extrapolated to the grand unified theory scale are satisfied, including the Gatto relation. The novel ingredient is the asymmetry of the down-quark and charged lepton Yukawa matrices. Explaining the reactor angle requires a CP phase in the TBM matrix, resulting in the Jarlskog-Greenberg invariant at |J|=0.028, albeit with an undetermined sign. While SO(10) restrains the right-handed neutrino Majorana matrix, the neutrino masses are left undetermined.

  • Tomography by neutrino pair beam
    OU-HET 973
    Phys.Lett. B785 (2018) 536-542

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

    We consider tomography of the Earth's interior using the neutrino pair beam which has recently been proposed. The beam produces a large amount of neutrino and antineutrino pairs from the circulating partially stripped ions and provides the possibility to measure precisely the energy spectrum of neutrino oscillation probability together with a sufficiently large detector. It is shown that the pair beam gives a better sensitivity to probe the Earth's crust compared with the neutrino sources at present. In addition we present a method to reconstruct a matter density profile by means of the analytic formula of the oscillation probability in which the matter effect is included perturbatively to the second order.

  • Predictive neutrino mass textures with origin of flavor symmetries
    APCTP Pre2018 - 011
    Phys.Rev. D98 (2018) 055025

    by: Kobayashi, Tatsuo (Hokkaido U.) et al.

    We investigate origins of predictive one-zero neutrino mass textures in a systematic way. Here we search Abelian continuous(discrete) global symmetries, and non-Abelian discrete symmetries, and show how to realize these neutrino masses. Then we propose a concrete model involving a dark matter candidate and an extra gauge boson, and show their phenomenologies.

  • Invisible Neutrino Decay Could Resolve IceCube’s Track and Cascade Tension
    Phys.Rev.Lett. 121 (2018) 121802

    by: Denton, Peter B. (DARK Cosmology Ctr.) et al.

    The IceCube Neutrino Observatory detects high energy astrophysical neutrinos in two event topologies: tracks and cascades. Since the flavor composition of each event topology differs, tracks and cascades can be used to test the neutrino properties and the mechanisms behind the neutrino production in astrophysical sources. Assuming a conventional model for the neutrino production, the IceCube data sets related to the two channels are in $>3\sigma$ tension with each other. Invisible neutrino decay with lifetime $\tau/m=10^2$ s/eV solves this tension. Noticeably, it leads to an improvement over the standard non-decay scenario of more than $3\sigma$ while remaining consistent with all other multi-messenger observations. In addition, our invisible neutrino decay model predicts a reduction of $59\%$ in the number of observed $\nu_\tau$ events which is consistent with the current observational deficit.

  • Leptonic $CP$ Violation and Proton Decay in SUSY SO(10)
    JHEP 1809 (2018) 119

    by: Mohapatra, Rabindra N. (Maryland U.) et al.

    We study the correlation between proton lifetime and leptonic CP violation in a class of renormalizable supersymmetric SO(10) grand unified theories (GUTs) with 10, 126 and 120 Higgs fields, which provides a unified description of all fermion masses and a possible resolution for the strong CP problem. This specific model is unique in that it can so far be compatible with current proton lifetime limits for a supersymmetry (SUSY) breaking scale as low as 5 TeV due to the presence of a specific Yukawa texture. Our investigation reveals that a discovery of leptonic CP violation in neutrino oscillations would lead to substantial reduction of the parameter space of the model and the potential ruling out of type-II dominance in the neutrino mass seesaw. Furthermore, the previously predicted proton partial lifetimes are sufficiently long for only certain values of the leptonic CP phase.

  • Pendulum Leptogenesis
    Phys.Lett. B785 (2018) 184-190

    by: Bamba, Kazuharu (Fukushima U.) et al.

    We propose a new non-thermal Leptogenesis mechanism that takes place during the reheating epoch, and utilizes the Ratchet mechanism. The interplay between the oscillation of the inflaton during reheating and a scalar lepton leads to a dynamical system that emulates the well-known forced pendulum. This is found to produce driven motion in the phase of the scalar lepton which leads to the generation of a non-zero lepton number density that is later redistributed to baryon number via sphaleron processes. This model successfully reproduces the observed baryon asymmetry, while simultaneously providing an origin for neutrino masses via the seesaw mechanism.

  • Breaking flavor democracy with symmetric perturbations
    Phys.Lett. B785 (2018) 268-273

    by: Ghosh, Tathagata (Hawaii U.) et al.

    Flavor democracy broken in the fermion mass matrix by means of small perturbations can give rise to hierarchical fermion masses. We study the breaking of the $S^L_3 \times S^R_3$ symmetry associated with democratic mass matrices to a smaller exchange symmetry $S^L_2 \times S^R_2$ in the charged lepton, up and down quark sectors. An additional breaking of the $S^L_2 \times S^R_2$ symmetry is necessary for the down quark mass matrix, which yields arbitrary perturbations in that sector. On the other hand, we require the neutrino mass matrix to be diagonal at the leading order, with the perturbations left arbitrary due to the absence of any guiding symmetry. We show that the interplay between these two kinds of perturbations reproduces the quark and lepton mass and mixing observables for either hierarchy of neutrino masses.

  • Matter effects in neutrino visible decay at future long-baseline experiments
    Eur.Phys.J. C78 (2018) 809

    by: Ascencio-Sosa, M.V. (Lima, Pont. U. Catolica) et al.

    Neutrino visible decay in the presence of matter is re-evaluated. We study these effects in two future long-baseline experiments where matter effects are relevant: DUNE (1300 km) and a hypothetical beam aimed towards ANDES (7650 km). We find that matter effects are negligible for the visible component of neutrino decay at DUNE, being much more relevant at ANDES. We perform a detailed simulation of DUNE, considering $\nu_\mu$ disappearance and $\nu_e$ appearance channels, for both FHC and RHC modes. The sensitivity to the decay constant $\alpha_3$ can be as low as $2\times10^{-6}$ eV$^2$ at 90% C.L., depending on the neutrino masses and type of coupling. We also show the impact of neutrino decay in the determination of $\theta_{23}$ and $\delta_{\rm CP}$, and find that the best-fit value of $\theta_{23}$ can move from a true value at the lower octant towards the higher octant.

  • Three-loop neutrino masses via new massive gauge bosons from $E_6$ GUT
    Phys.Rev. D98 (2018) 055028

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

    We propose a SU(3)C×SU(2)L×SU(2)N×U(1)Y model arising from E6 grand unified theory. We show that the tiny neutrino masses in this model can be generated at the three-loop involving the SU(2)N gauge bosons. With Yukawa couplings around 0.01 or larger and TeV-scale SU(2)N gauge bosons, we show that the neutrino oscillation data can be explained naturally by presenting a concrete benchmark set of input parameters. All new particles are around the TeV scale. Thus our model can be tested at the ongoing/future collider experiments.

  • Constraining Non-Cold Dark Matter Models with the Global 21-cm Signal
    Phys.Rev. D98 (2018) 063021

    by: Schneider, Aurel (ETH, Zurich (main))

    Any particle dark matter (DM) scenario featuring a suppressed power spectrum of astrophysical relevance results in a delay of galaxy formation. As a consequence, such scenarios can be constrained using the global 21-cm absorption signal initiated by the UV radiation of the first stars. The Experiment to Detect the Global Epoch of Reionization Signature (EDGES) recently reported the first detection of such an absorption signal at redshift $\sim 17$. While its amplitude might indicate the need for new physics, we solely focus on the timing of the signal to test non-cold DM models. Assuming conservative limits for the stellar-to-baryon fraction ($f_{*}<0.03$) and for the minimum cooling temperature ($T_{\rm vir}>10^3$ Kelvin) motivated by radiation-hydrodynamic simulations, we are able to derive unprecedented constraints on a variety of non-cold DM models. For example, the mass of thermal warm DM is limited to $m_{\rm TH}>6.1$ keV, while mixed DM scenarios (featuring a cold and a hot component) are constrained to a hot DM fraction below 17 percent. The ultra-light axion DM model is limited to masses $m_{a}>8\times10^{-21}$ eV, a regime where its wave-like nature is pushed far below the kiloparsec scale. Finally, sterile neutrinos from resonant production can be fully disfavoured as a dominant DM candidate. The results of this paper show that the 21-cm absorption signal is a powerful discriminant of non-cold dark matter, allowing for significant improvements over to the strongest current limits. Confirming the result from EDGES is paramount in this context.

  • Hybrid seesaw leptogenesis and TeV singlets
    Phys.Lett. B785 (2018) 489-497

    by: Agashe, Kaustubh (Maryland U.) et al.

    The appealing feature of inverse seesaw models is that the Standard Model (SM) neutrino mass emerges from the exchange of TeV scale singlets with sizable Yukawa couplings, which can be tested at colliders. However, the tiny Majorana mass splitting between TeV singlets, introduced to accommodate small neutrino masses, is left unexplained. Moreover, we argue that these models suffer from a structural limitation that prevents a successful leptogenesis if one insists on having unsuppressed Yukawa couplings and TeV scale singlets. In this work we propose a hybrid seesaw model, where we replace the mass splitting with a coupling to a high scale seesaw module including a TeV scalar. We show that this structure achieves the goal of filling both the above gaps with couplings of order unity. The necessary structure automatically arises embedding the seesaw mechanism in composite Higgs models, but may also be enforced by new gauge symmetries in a weakly-coupled theory. Our hybrid seesaw models have distinguishing features compared to the standard high scale type-I seesaw and inverse seesaw. Firstly, they have much richer phenomenology. Indeed, they generally predict new TeV scale physics (including scalars) potentially accessible at present and future colliders, whereas weakly-coupled versions may also have cosmological signature due to the presence of a light Nambu–Goldstone boson coupled to neutrinos. Secondly, our scenario features an interesting interplay between high scale and TeV scale physics in leptogenesis and enlarges the range of allowed high scale singlet masses beyond the usual ∼109–1015GeV , without large hierarchies in the Yukawa couplings nor small mass splitting among the singlets.

  • R(D$^{(∗)}$) from W$^{′}$ and right-handed neutrinos
    JHEP 1809 (2018) 169

    by: Greljo, Admir (U. Mainz, PRISMA) et al.

    We provide an ultraviolet (UV) complete model for the R(D$^{(∗)}$) anomalies, in which the additional contribution to semi-tauonic b → c transitions arises from decay to a right-handed sterile neutrino via exchange of a TeV-scale SU(2)$_{L}$ singlet W$^{′}$. The model is based on an extension of the Standard Model (SM) hypercharge group, U(1)$_{Y}$ , to the SU(2)$_{V}$ × U(1)$^{′}$ gauge group, containing several pairs of heavy vector-like fermions. We present a comprehensive phenomenological survey of the model, ranging from the low-energy flavor physics, direct searches at the LHC, to neutrino physics and cosmology. We show that, while the W$^{′}$ and Z$^{′}$-induced constraints are important, it is possible to find parameter space naturally consistent with all the available data. The sterile neutrino sector also offers rich phenomenology, including possibilities for measurable dark radiation, gamma ray signals, and displaced decays at colliders.

  • A singlet doublet dark matter model with radiative neutrino masses
    JHEP 1810 (2018) 055

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

    We present a detailed study of a combined singlet-doublet scalar and singlet-doublet fermion model for dark matter. These models have only been studied separately in the past. We show that their combination allows for the radiative generation of neutrino masses, but that it also implies the existence of lepton-flavour violating (LFV) processes. We first analyse the dark matter, neutrino mass and LFV aspects separately. We then perform two random scans for scalar dark matter imposing Higgs mass, relic density and neutrino mass constraints, one over the full parameter space, the other over regions where scalar-fermion coannihilations become important. In the first case, a large part of the new parameter space is excluded by LFV, and the remaining models will be probed by XENONnT. In the second case, direct detection cross sections are generally too small, but a substantial part of the viable models will be tested by future LFV experiments. Possible constraints from the LHC are also discussed.

  • Naumov- and Toshev-like relations in the renormalization-group evolution of quarks and Dirac neutrinos
    Chin.Phys. C42 (2018) 103105

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

    In an analytical way of studying matter effects on neutrino oscillations, the Naumov and Toshev relations have been derived to respectively link the Jarlskog invariant of CP violation and the Dirac phase in the standard parametrization of the $3\times 3$ flavor mixing matrix to their matter-corrected counterparts. Here we show that there exist similar relations for Dirac neutrinos and charged leptons evolving with energy scales via the one-loop renormalization-group (RG) equations in the tau-dominance approximation, and for the running behaviors of up- and down-type quarks in the top-dominance approximation, provided a different parametrization is taken into account.

  • Natural Alignment of Quark Flavors and Radiatively Induced Quark Mixings
    Phys.Rev. D98 (2018) 073002

    by: Dev, Abhish (Maryland U.) et al.

    The standard model does not provide an explanation of the observed alignment of quark flavors i.e. why are the up and down quarks approximately aligned in their weak interactions according to their masses? We suggest a resolution of this puzzle using a combination of left-right and Peccei-Quinn (PQ) symmetry. The quark mixings in this model vanish at the tree level and arise out of one loop radiative corrections which explain their smallness. The lepton mixings, on the other hand, appear at the tree level and are therefore larger. We show that all fermion masses and mixings can be fitted with a reasonable choice of parameters. The neutrino mass fit using seesaw mechanism requires the right-handed WR mass bigger than 18 TeV. Due to the presence of PQ symmetry, this model clearly provides a solution to the strong CP problem.

  • Looking for the left sneutrino LSP with displaced-vertex searches
    Phys.Rev. D98 (2018) 075004

    by: Lara, Iñaki (Madrid, IFT) et al.

    We analyze a displaced dilepton signal expected at the LHC for a tau left sneutrino as the lightest supersymmetric particle with a mass in the range 45–100 GeV. The sneutrinos are pair produced via a virtual W, Z or γ in the s channel and, given the large value of the tau Yukawa coupling, their decays into two dileptons or a dilepton plus missing transverse energy from neutrinos can be significant. The discussion is carried out in the framework of the μνSSM, where the presence of R-parity violating couplings involving right-handed neutrinos solves the μ problem and can reproduce the neutrino data. To probe the tau left sneutrinos we compare the predictions of this scenario with the ATLAS search for long-lived particles using displaced lepton pairs in pp collisions at s=8  TeV, allowing us to constrain the parameter space of the model. We also consider an optimization of the trigger requirements used in existing displaced-vertex searches by means of a high level trigger that exploits tracker information. This optimization is generically useful for a light metastable particle decaying into soft charged leptons. The constraints on the sneutrino turn out to be more stringent. We finally discuss the prospects for the 13 TeV LHC searches as well as further potential optimizations.

  • Modifications to the neutrino mixing from the μ - τ reflection symmetry
    Nucl.Phys. B935 (2018) 129-143

    by: Zhao, Zhen-hua (Liaoning Normal U.)

    The μ - τ reflection symmetry serves as a unique basis for understanding the observed neutrino mixing as it can lead us to the interesting results θ23=π/4 and δ=−π/2 which stand close to the current experimental results. But a precise measurement for θ23 and δ will probably force us to modify the neutrino mixing U(0) from such a symmetry. Here we perform a study for modifications to U(0) in the forms of U(1)†U(0) and U(0)U(1) where U(1)=Rij(1) (for ij=12,23 and 13) with Rij(1) denoting a real orthogonal rotation on the ij plane.

  • IceCube bounds on sterile neutrinos above 10 eV
    SISSA 09/2018/FISI
    Eur.Phys.J. C78 (2018) 807

    by: Blennow, Mattias (Madrid, IFT) et al.

    We study the capabilities of IceCube to search for sterile neutrinos with masses above 10 eV by analyzing its $\nu_\mu$ disappearance atmospheric neutrino sample. We find that IceCube is not only sensitive to the mixing of sterile neutrinos to muon neutrinos, but also to the more elusive mixing with tau neutrinos through matter effects. The currently released 1-year data shows a mild (around 2$\sigma$) preference for non-zero sterile mixing, which overlaps with the favoured region for the sterile neutrino interpretation of the ANITA upward shower. Although the null results from CHORUS and NOMAD on $\nu_\mu$ to $\nu_\tau$ oscillations in vacuum disfavour the hint from the IceCube 1-year data, the relevant oscillation channel and underlying physics are different. At the $99\%$ C.L. an upper bound is obtained instead that improves over the present Super-Kamiokande and DeepCore constraints in some parts of the parameter space. We also investigate the physics reach of the roughly 8 years of data that is already on tape as well as a forecast of 20 years data to probe the present hint or improve upon current constraints.

  • The first $\Delta(27)$ flavor 3-3-1 model with low scale seesaw mechanism
    Eur.Phys.J. C78 (2018) 804

    by: Cárcamo Hernández, A.E. (Santa Maria U., Valparaiso) et al.

    We propose a viable model based on the $SU(3)_C\times SU(3)_L\times U(1)_X$ gauge group, augmented by the $U(1)_{L_g}$ global lepton number symmetry and the $\Delta(27) \times Z_3\times Z_{16}$ discrete group, capable of explaining the Standard Model (SM) fermion masses and mixings, and having a low scale seesaw mechanism which can be tested at the LHC. In addition the model provides an explanation for the SM fermion masses and mixings. In the proposed model, small masses for the light active neutrinos are generated by an inverse seesaw mechanism caused by non renormalizable Yukawa operators and mediated by three very light Majorana neutrinos and the observed hierarchy of the SM fermion masses and mixing angles is produced by the spontaneous breaking of the $\Delta(27) \times Z_{3}\times Z_{16}$ symmetry at very large energy scale. This neutrino mass generation mechanism is not presented in our previous 3-3-1 models with $\Delta(27)$ group (Nucl.Phys. B913 (2016) 792-814 and Eur.Phys.J. C76 (2016) no.5, 242), where the masses of the light active neutrinos arise from a combination of type I and type II seesaw mechanisms (Nucl.Phys. B913 (2016) 792-814) as well as from a double seesaw mechanism (Eur.Phys.J. C76 (2016) no.5, 242). Thus, this work corresponds to the first implementation of the $\Delta(27)$ symmetry in a 3-3-1 model with low scale seesaw mechanism.

  • Investigation of Dark Matter in the 3-2-3-1 Model
    Phys.Rev. D98 (2018) 055033

    by: Huong, D.T. (Hanoi Ed. U.) et al.

    We prove that the $SU(3)_C\otimes SU(2)_L \otimes SU(3)_R\otimes U(1)_X$ (3-2-3-1) gauge model always contains a matter parity $W_P=(-1)^{3(B-L)+2s}$ as conserved residual gauge symmetry, where $B-L=2(\beta T_{8R}+X)$ is a $SU(3)_R\otimes U(1)_X$ charge. Due to the non-Abelian nature of $B-L$, the $W$-odd and $W$-even fields are actually unified in gauge multiplets. We investigate two viable versions for dark matter according to $\beta=\pm1/\sqrt{3}$, where the dark matter candidates can be fermion, scalar, or vector fields. We figure out the parameter spaces in the allowed regions of the relic density and direct detection cross-sections. Additionally, we examine the neutrino masses induced by the seesaw mechanism along with associated lepton flavor violation processes. The new gauge boson searches at the LEPII and LHC are discussed.

  • Neutrinoless double-beta decay with massive scalar emission
    Phys.Lett. B785 (2018) 354-361

    by: Blum, Kfir (Weizmann Inst.) et al.

    Searches for neutrino-less double-beta decay ( 0ν2β ) place an important constraint on models where light fields beyond the Standard Model participate in the neutrino mass mechanism. While 0ν2β experimental collaborations often consider various massless majoron models, including various forms of majoron couplings and multi-majoron final-state processes, none of these searches considered the scenario where the “majoron” ϕ is not massless, mϕ∼ MeV, of the same order as the Q -value of the 0ν2β reaction. We consider this parameter region and estimate 0ν2βϕ constraints for mϕ of order MeV. The constraints are affected not only by kinematical phase space suppression but also by a change in the signal to background ratio charachterizing the search. As a result, 0ν2βϕ constraints for mϕ>0 diminish significantly below the reaction threshold. This has phenomenological implications, which we illustrate focusing on high-energy neutrino telescopes. The spectral shape of high-energy astrophysical neutrinos could exhibit features due to resonant νν→ϕ→νν scattering. Such features fall within the sensitivity range of IceCube-like experiments, if mϕ is of order MeV, making 0ν2βϕ a key complimentary laboratory constraint on the scenario. Our results motivate a dedicated analysis by 0ν2β collaborations, analogous to the dedicated analyses targeting massless majoron models.

  • Hydrodynamical Neutron-star Kicks in Electron-capture Supernovae and Implications for the CRAB Supernova
    Astrophys.J. 865 (2018) 61

    by: Gessner, Alexandra (Dresden, Max Planck Inst.) et al.

    Neutron stars (NSs) obtain kicks, typically of several 100 km s−1, at birth. The gravitational tugboat mechanism can explain these kicks as consequences of asymmetric mass ejection during the supernova (SN) explosion. Support for this hydrodynamic explanation is provided by observations of SN remnants with associated NSs, which confirm the prediction that the bulk of the explosion ejecta, particularly the chemical elements between silicon and the iron group, are dominantly expelled in the hemisphere opposite to the direction of the NS kick. Here, we present a large set of two- and three-dimensional explosion simulations of electron-capture SNe, considering explosion energies between ∼3 × 1049 erg and ∼1.6 × 1050 erg. We find that the fast acceleration of the SN shock in the steep density gradient delimiting the O–Ne–Mg core of the progenitor enables such a rapid expansion of neutrino-heated matter that the growth of neutrino-driven convection freezes out quickly in a high-mode spherical harmonics pattern. Because the corresponding momentum asymmetry of the ejecta is very small and the gravitational acceleration by the fast-expanding ejecta abates rapidly, the NS kick velocities are a few km s−1, at most. The extremely low core compactness of O–Ne–Mg-core progenitors therefore favors hydrodynamic NS kicks much below the ∼160 km s−1 measured for the Crab pulsar. This suggests either that the Crab Nebula is not the remnant of an electron-capture SN, but rather of a low-mass iron-core progenitor; or that the Crab pulsar was not accelerated by the gravitational tugboat mechanism, but instead received its kick by a non-hydrodynamic mechanism such as, e.g., anisotropic neutrino emission.

  • Phenomenology of colored radiative neutrino mass model and its implications on cosmic-ray observations
    Chin.Phys. C42 (2018) 103101

    by: Ding, Ran (Peking U., CHEP) et al.

    We extend the colored Zee-Babu model with a gauged $U(1)_{B-L}$ symmetry and a scalar singlet dark matter (DM) candidate $S$. The spontaneous breaking of $U(1)_{B-L}$ leaves a residual $Z_2$ symmetry that stabilizes the DM and generates tiny neutrino mass at the two-loop level with the color seesaw mechanism. After investigating dark matter and flavor phenomenology of this model systematically, we further focus on its imprint on two of cosmic-ray anomalies: the Fermi-LAT gamma-ray excess at the Galactic Center (GCE) and the PeV ultra-high energy (UHE) neutrino events at the IceCube. We found that the Fermi-LAT GCE spectrum can be well fitted by DM annihilation into a pair of on-shell singlet Higgs mediators while being compatible with the constraints from relic density, direct detections as well as dwarf spheroidal galaxies in the Milky Way. Although the UHE neutrino events at the IceCube could be accounted for by resonance production of a TeV-scale leptoquark, the relevant Yukawa couplings have been severely limited by current low energy flavor experiments. We then derive the IceCube limits on the Yukawa couplings by employing its latest 6-year data.

  • Dirac neutrino mixings from hidden μ – τ symmetry
    Phys.Lett. B785 (2018) 51-58

    by: Luna Terrazas, Edgar R. (CINVESTAV, IPN) et al.

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

  • Constraints on the sum of the neutrino masses in dynamical dark energy models with $w(z) \geq -1$ are tighter than those obtained in $\Lambda$CDM
    Phys.Rev. D98 (2018) 083501

    by: Vagnozzi, Sunny (Stockholm U., OKC) et al.

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

  • Indications of an unexpected signal associated with the GW170817 binary neutron star inspiral
    Astropart.Phys. 103 (2018) 1-6

    by: Fischbach, E. (Purdue U.) et al.

    We report experimental evidence at the 2.5 σ level for an unexpected signal associated with the GW170817 binary neutron star inspiral. This evidence derives from a laboratory experiment simultaneously measuring the β -decay rates of Si-32 and Cl-36 in a common detector. Whereas the Si-32 and Cl-36 decay rates show no statistical correlation before or after the inspiral, they are highly correlated (∼95%) in the 5-h time interval immediately following the inspiral. If we interpret this correlation as arising from the influence of particles emitted during the inspiral, then we can estimate the mass m x of these particles from the time delay between the gravity-wave signal and a peak in the β -decay data. We find for particles of energy 10 MeV, m x  ≲  16 eV which includes the neutrino mass region m ν  ≲  2 eV. The latter is based on existing limits for the masses m i of the three known neutrino flavors. Additionally, we find that the correlation is even stronger if we include data in the 80 minute period before the arrival of the gravity wave signal. Given the large number of radionuclides whose decays are being monitored at any given time, we conjecture that other groups may also be in a position to search for statistically suggestive fluctuations of radionuclide decay rates associated with the GW170817 inspiral, and possibly with other future inspirals.

  • $W^+ W^- H$ production at lepton colliders: a new hope for heavy neutral leptons
    Eur.Phys.J. C78 (2018) 795

    by: Baglio, Julien (Tubingen U.) et al.

    We present the first study of the production of a Standard Model Higgs boson at a lepton collider in association with a pair of W bosons, $e^+_{} e^-_{} \rightarrow W^+_{} W^-_{} H$ , in the inverse seesaw model. Taking into account all relevant experimental and theoretical constraints, we find sizable effects due to the additional heavy neutrinos up to $-38\%$ on the total cross-section at a center-of-mass energy of 3 TeV, and even up to $-66\%$ with suitable cuts. This motivates a detailed sensitivity analysis of the process $e^+_{} e^-_{} \rightarrow W^+_{} W^-_{} H$ as it could provide a new, very competitive experimental probe of low-scale neutrino mass models.

  • PArthENoPE reloaded
    Comput.Phys.Commun. 233 (2018) 237-242

    by: Consiglio, R. (Naples U.) et al.

    We describe the main features of a new and updated version of the program PArthENoPE , which computes the abundances of light elements produced during Big Bang Nucleosynthesis. As the previous first release in 2008, the new one, PArthENoPE2.0 , is publicly available and distributed from the code site, . Apart from minor changes, which will be also detailed, the main improvements are as follows. The powerful, but not freely accessible, NAG routines have been substituted by ODEPACK libraries, without any significant loss in precision. Moreover, we have developed a Graphical User Interface (GUI) which allows a friendly use of the code and a simpler implementation of running for grids of input parameters.

  • Dark matter assisted Dirac leptogenesis and neutrino mass
    Nucl.Phys. B936 (2018) 76-90

    by: Narendra, Nimmala (Indian Inst. Tech., Hyderabad) et al.

    We propose an extension of the standard model with U(1)B–L×Z2 symmetry. In this model by assuming that the neutrinos are Dirac ( i.e. B–L is an exact symmetry), we found a simultaneous solution for non zero neutrino masses and dark matter content of the universe. The observed baryon asymmetry of the universe is also explained using Dirac Leptogenesis, which is assisted by a dark sector, gauged under a U(1)D symmetry. The latter symmetry of the dark sector is broken at a TeV scale and thereby giving mass to a neutral gauge boson ZD . The standard model Z-boson mixes with the gauge boson ZD at one loop level and paves a way to detect the dark matter through spin independent elastic scattering at terrestrial laboratories.

  • Neutrinoless Double Beta Decay and the Baryon Asymmetry of the Universe
    DO-TH 17/19
    CP3-Origins-2017-055 DNRF90
    Phys.Rev. D98 (2018) 055029

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

    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 nonstandard 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.

  • Multi-lepton signatures of additional scalar bosons beyond the Standard Model at the LHC
    J.Phys. G45 (2018) 115003

    by: von Buddenbrock, Stefan (U. Witwatersrand, Johannesburg, Sch. Phys.) et al.

    Following a prediction made in Refs.~\cite{vonBuddenbrock:2015ema,Kumar:2016vut,vonBuddenbrock:2016rmr}, this paper focuses on multi-lepton signatures arising from two new hypothetical 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 and the other being in association with top quarks. The $H \to S h$ decay mode is considered, where leptonic final states are studied. The CP properties of $S$ are characterised by considering effective couplings derived from dimension six operators through $SWW$ 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 $Z, W$ and $S$ bosons. The predictions of the models are compared both to ATLAS and CMS results at $\sqrt{s} = 8$ and $13$~TeV, where appropriate. The data is interpreted using a simplified model where all the signal comes from $H \to S h$, assuming $S$ to be Higgs-like, $m_H=270$~GeV and $m_S=150$~GeV. The combined result yields gives a best fit value for the parameter $\beta_g$ (the strength of the Yukawa coupling of $H$ to top quarks), $\beta_g^2=1.38\pm 0.22$. A number of regions of the phase space are suggested to the experiments for further exploration.

  • Challenges posed by non-standard neutrino interactions in the determination of $\delta_{CP}$ at DUNE
    Nucl.Phys. B936 (2018) 91-105

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

    One of the primary objectives of the Deep Underground Neutrino Experiment (DUNE) is to discover the leptonic CP violation and to identify its 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 ϵee=−1 and δCP=±90° .

  • Probing Leptogenesis at Future Colliders
    JHEP 1809 (2018) 124

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

    We investigate the question whether leptogenesis, as a mechanism for explaining the baryon asymmetry of the universe, can be tested at future colliders. Focusing on the minimal scenario of two right-handed neutrinos, we identify the allowed parameter space for successful leptogenesis in the heavy neutrino mass range between 5 and 50 GeV. Our calculation includes the lepton flavour violating contribution from heavy neutrino oscillations as well as the lepton number violating contribution from Higgs decays to the baryon asymmetry of the universe. We confront this parameter space region with the discovery potential for heavy neutrinos at future lepton colliders, which can be very sensitive in this mass range via displaced vertex searches. Beyond the discovery of heavy neutrinos, we study the precision at which the flavour-dependent active-sterile mixing angles can be measured. The measurement of these mixing angles at future colliders can test whether a minimal type I seesaw mechanism is the origin of the light neutrino masses, and it can be a first step towards probing leptogenesis as the mechanism of baryogenesis. We discuss how a stronger test could be achieved with an additional measurement of the heavy neutrino mass difference.

  • Light scalars and dark photons in Borexino and LSND experiments
    Phys.Lett. B785 (2018) 288-295

    by: Pospelov, Maxim (Perimeter Inst. Theor. Phys.) et al.

    Bringing an external radioactive source close to a large underground detector can significantly advance sensitivity not only to sterile neutrinos but also to “dark” gauge bosons and scalars. Here we address in detail the sensitivity reach of the Borexino-SOX configuration, which will see a powerful (a few PBq) 144 Ce– 144 Pr source installed next to the Borexino detector, to light scalar particles coupled to the SM fermions. The mass reach of this configuration is limited by the energy release in the radioactive γ -cascade, which in this particular case is 2.2 MeV. Within that reach one year of operations will achieve an unprecedented sensitivity to coupling constants of such scalars, reaching down to g∼10−7 levels and probing significant parts of parameter space not excluded by either beam dump constraints or astrophysical bounds. Should the current proton charge radius discrepancy be caused by the exchange of a MeV-mass scalar, then the simplest models will be decisively probed in this setup. We also update the beam dump constraints on light scalars and vectors, and in particular rule out dark photons with masses below 1 MeV, and couplings ϵ≥10−5 .

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