1,953 research outputs found

    Supernova Bounds on keV-mass Sterile Neutrinos

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    Sterile neutrinos of keV masses are one of the most promising candidates for the warm dark matter, which could solve the small-scale problems encountered in the scenario of cold dark matter. We present a detailed study of the production of such sterile neutrinos in a supernova core, and derive stringent bounds on the active-sterile neutrino mixing angles and sterile neutrino masses based on the standard energy-loss argument.Comment: 10 pages, 2 figures, to be published in the Proceedings of International Conference on Massive Neutrinos, Singapore, February 9-13, 2015. arXiv admin note: text overlap with arXiv:1109.318

    Extrinsic and Intrinsic CPT Asymmetries in Neutrino Oscillations

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    We reconsider the extrinsic and possible intrinsic CPT violation in neutrino oscillations, and point out an identity, i.e., AαβCP=AβαCPT+AαβTA^{\rm CP}_{\alpha \beta} = A^{\rm CPT}_{\beta \alpha} + A^{\rm T}_{\alpha \beta}, among the CP, T, and CPT asymmetries in oscillations. For three-flavor oscillations in matter of constant density, the extrinsic CPT asymmetries AeeCPTA^{\rm CPT}_{ee}, AeμCPTA^{\rm CPT}_{e\mu}, AμeCPTA^{\rm CPT}_{\mu e}, and AμμCPTA^{\rm CPT}_{\mu \mu} caused by Earth matter effects have been calculated in the plane of different neutrino energies and baseline lengths. It is found that two analytical conditions can be implemented to describe the main structure of the contours of vanishing extrinsic CPT asymmetries. Finally, without assuming intrinsic CPT symmetry in the neutrino sector, we investigate the possibility to constrain the difference of the neutrino CP-violating phase δ\delta and the antineutrino one δ\overline{\delta} using a low-energy neutrino factory and the super-beam experiment ESSν\nuSB. We find that δδ0.35π|\delta - \overline{\delta}| \lesssim 0.35\pi in the former case and δδ0.7π|\delta - \overline{\delta}| \lesssim 0.7\pi in the latter case can be achieved at the 3σ3\sigma confidence level if δ=δ=π/2\delta = \overline{\delta} = \pi/2 is assumed.Comment: 26 pages, 6 figures, more discussions added, matches the published versio

    Relic Right-handed Dirac Neutrinos and Implications for Detection of Cosmic Neutrino Background

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    It remains to be determined experimentally if massive neutrinos are Majorana or Dirac particles. In this connection, it has been recently suggested that the detection of cosmic neutrino background of left-handed neutrinos νL\nu^{}_{\rm L} and right-handed antineutrinos νR\overline{\nu}^{}_{\rm R} in future experiments of neutrino capture on beta-decaying nuclei (e.g., νe+3H3He+e\nu^{}_e + {^3{\rm H}} \to {^3}{\rm He} + e^- for the PTOLEMY experiment) is likely to distinguish between Majorana and Dirac neutrinos, since the capture rate is twice larger in the former case. In this paper, we investigate the possible impact of right-handed neutrinos on the capture rate, assuming that massive neutrinos are Dirac particles and both right-handed neutrinos νR\nu^{}_{\rm R} and left-handed antineutrinos νL\overline{\nu}^{}_{\rm L} can be efficiently produced in the early Universe. It turns out that the capture rate can be enhanced at most by 28%28\% due to the presence of relic νR\nu^{}_{\rm R} and νL\overline{\nu}^{}_{\rm L} with a total number density of 95 cm395~{\rm cm}^{-3}, which should be compared to the number density 336 cm3336~{\rm cm}^{-3} of cosmic neutrino background. The enhancement has actually been limited by the latest cosmological and astrophysical bounds on the effective number of neutrino generations Neff=3.140.43+0.44N^{}_{\rm eff} = 3.14^{+0.44}_{-0.43} at the 95%95\% confidence level. For illustration, two possible scenarios have been proposed for thermal production of right-handed neutrinos in the early Universe.Comment: 16 pages, 4 figure, more discussions added, references updated, to appear in Nucl. Phys.

    A Further Study of the Frampton-Glashow-Yanagida Model for Neutrino Masses, Flavor Mixing and Baryon Number Asymmetry

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    In light of the latest neutrino oscillation data, we revisit the minimal scenario of type-I seesaw model, in which only two heavy right-handed Majorana neutrinos are introduced to account for both tiny neutrino masses and the baryon number asymmetry in our Universe. In this framework, we carry out a systematic study of the Frampton-Glashow-Yanagida ansatz by taking into account the renormalization-group running of neutrino mixing parameters and the flavor effects in leptogenesis. We demonstrate that the normal neutrino mass ordering is disfavored even in the minimal supersymmetric standard model with a large value of tanβ\tan \beta, for which the running effects could be significant. Furthermore, it is pointed out that the original scenario with a hierarchical mass spectrum of heavy Majorana neutrinos contradicts with the upper bound derived from a naturalness criterion, and the resonant mechanism with nearly-degenerate heavy Majorana neutrinos can be a possible way out.Comment: 24 pages, 4 figures, 2 tables, more discussions added, to appear in JHE

    Quark Flavor Mixings from Hierarchical Mass Matrices

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    In this paper, we extend the Fritzsch ansatz of quark mass matrices while retaining their hierarchical structures and show that the main features of the Cabibbo-Kobayashi-Maskawa (CKM) matrix VV, including VusVcd|V^{}_{us}| \simeq |V^{}_{cd}|, VcbVts|V^{}_{cb}| \simeq |V^{}_{ts}| and Vub/Vcb<Vtd/Vts|V^{}_{ub}|/|V^{}_{cb}| < |V^{}_{td}|/|V^{}_{ts}|, can be well understood. This agreement is observed especially when the mass matrices have non-vanishing (1,3)(1,3) and (3,1)(3,1) off-diagonal elements. The phenomenological consequences of these for the allowed texture content and gross structural features of `hierarchical' quark mass matrices are addressed from a model independent prospective under the assumption of factorizable phases in these. The approximate and analytical expressions of the CKM matrix elements are derived, and a detailed analysis reveals that such structures are in good agreement with the observed quark flavor mixing angles and the CP-violating phase at the 1σ1\sigma level and call upon a further investigation of the realization of these structures from a top-down prospective.Comment: 8 pages, 3 figures, Accepted for publication in European Physical Journal