1,953 research outputs found

### Supernova Bounds on keV-mass Sterile Neutrinos

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

We reconsider the extrinsic and possible intrinsic CPT violation in neutrino
oscillations, and point out an identity, i.e., $A^{\rm CP}_{\alpha \beta} =
A^{\rm CPT}_{\beta \alpha} + A^{\rm T}_{\alpha \beta}$, among the CP, T, and
CPT asymmetries in oscillations. For three-flavor oscillations in matter of
constant density, the extrinsic CPT asymmetries $A^{\rm CPT}_{ee}$, $A^{\rm
CPT}_{e\mu}$, $A^{\rm CPT}_{\mu e}$, and $A^{\rm CPT}_{\mu \mu}$ 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 $\delta$ and the antineutrino one
$\overline{\delta}$ using a low-energy neutrino factory and the super-beam
experiment ESS$\nu$SB. We find that $|\delta - \overline{\delta}| \lesssim
0.35\pi$ in the former case and $|\delta - \overline{\delta}| \lesssim 0.7\pi$
in the latter case can be achieved at the $3\sigma$ confidence level if $\delta
= \overline{\delta} = \pi/2$ 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

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 $\nu^{}_{\rm
L}$ and right-handed antineutrinos $\overline{\nu}^{}_{\rm R}$ in future
experiments of neutrino capture on beta-decaying nuclei (e.g., $\nu^{}_e +
{^3{\rm H}} \to {^3}{\rm He} + e^-$ 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 $\nu^{}_{\rm R}$
and left-handed antineutrinos $\overline{\nu}^{}_{\rm L}$ can be efficiently
produced in the early Universe. It turns out that the capture rate can be
enhanced at most by $28\%$ due to the presence of relic $\nu^{}_{\rm R}$ and
$\overline{\nu}^{}_{\rm L}$ with a total number density of $95~{\rm cm}^{-3}$,
which should be compared to the number density $336~{\rm cm}^{-3}$ of cosmic
neutrino background. The enhancement has actually been limited by the latest
cosmological and astrophysical bounds on the effective number of neutrino
generations $N^{}_{\rm eff} = 3.14^{+0.44}_{-0.43}$ at the $95\%$ 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

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 $\tan \beta$, 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

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 $V$, including $|V^{}_{us}| \simeq
|V^{}_{cd}|$, $|V^{}_{cb}| \simeq |V^{}_{ts}|$ and $|V^{}_{ub}|/|V^{}_{cb}| <
|V^{}_{td}|/|V^{}_{ts}|$, can be well understood. This agreement is observed
especially when the mass matrices have non-vanishing $(1,3)$ and $(3,1)$
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 $1\sigma$ 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

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