All Results

Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

If massive neutrinos are Dirac particles, the proposed PTOLEMY experiment will hopefully be able to discover cosmic neutrino background via e+3H ! 3He+e? with a capture rate of ?D 4 yr?1. Recently, it has been pointed out that right-handed com-ponents of Dirac neutrinos could also be copiously produced in the early Universe and become an extra thermal or nonthermal ingredient of cosmic relic neutrinos, enhancing the capture rate to ?D 5:1 yr?1 or ?D 6:1 yr?1. In this work, we investigate the possibility to distinguish between thermal and nonthermal spectra of cosmic relic neu-trinos by measuring the annual modulation of the capture rate. For neutrino masses of 0:1 eV, we have found the amplitude of annual modulation in the standard case is M 0:05%, which will be increased to 0:1% and 0:15% in the presence of additional thermal and nonthermal right-handed neutrinos, respectively. The future detection of such a modulation will be helpful in understanding the Majorana or Dirac nature of massive neutrinos. |

Electroweak Vacuum Stability and Diphoton Excess at 750 GeV

Jue Zhang; Shun ZhouSubjects: Physics >> Nuclear Physics

Recently, both ATLAS and CMS collaborations at the CERN Large Hadron Collider (LHC) have announced their observations of an excess of diphoton events around the invariant mass of?750?GeV?with a local significance of?3.6σ?and?2.6σ, respectively. In this paper, we interpret the diphoton excess as the on-shell production of a real singlet scalar in the?pp→S→γγ?channel. To accommodate the observed production rate, we further introduce a vector-like fermion?F, which is carrying both color and electric charges. The viable regions of model parameters are explored for this simple extension of the Standard Model (SM). Moreover, we revisit the problem of electroweak vacuum stability in the same scenario, and find that the requirement for the electroweak vacuum stability up to high energy scales imposes serious constraints on the Yukawa coupling of the vector-like fermion and the quartic couplings of the SM Higgs boson and the new singlet scalar. Consequently, a successful explanation for the diphoton excess and the absolute stability of electroweak vacuum cannot be achieved simultaneously in this economical setup. |

Quark Flavor Mixings from Hierarchical Mass Matrices

Rohit Verma; Shun ZhouSubjects: Physics >> Nuclear Physics

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?|Vus|?|Vcd|,?|Vcb|?|Vts|?and?|Vub|/|Vcb|<|Vtd|/|Vts|, 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?1σ?level and call upon a further investigation of the realization of these structures from a top-down prospective. |

Theoretical Results on Neutrinos

Shun ZhouSubjects: Physics >> Nuclear Physics

In this talk, I first summarize our current knowledge about the fundamental properties of neutrinos and emphasize the remaining unsolved problems in neutrino physics. Then, recent theoretical results on neutrino mass models are introduced. Different approaches to understanding tiny neutrino masses, lepton flavor mixing and CP violation are presented. Finally, I report briefly some new progress in the studies of astrophysical neutrinos, including keV sterile neutrinos, supernova neutrinos and ultrahigh-energy cosmic neutrinos. |

Subjects: Physics >> Nuclear Physics

The latest results from atmospheric and accelerator neutrino experiments indicate that the normal neutrino mass ordering?m1 |

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

Jue Zhang; Shun ZhouSubjects: Physics >> Nuclear Physics

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?and right-handed antineutrinos?ν???R?in future experiments of neutrino capture on beta-decaying nuclei (e.g.,?νe+3H→3He+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?and left-handed antineutrinos?ν???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?νR?and?ν???L?with a total number density of?95?cm?3, which should be compared to the number density?336?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=3.14+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. |

Subjects: Physics >> Nuclear Physics

Motivated by recent intensive experimental efforts on searching for neutrinoless double-beta decays, we perform a detailed analysis of the physics potential of the experiments based on?76Ge. Assuming no signals, current and future experiments could place a?90%?lower limit on the half life?T0ν1/2?4×1026?yr?and?T0ν1/2?7×1027?yr, respectively. Then, how to report an evidence for neutrinoless double-beta decays is addressed by following the Bayesian statistical approach. For the first time, we present a quantitative description of experimental power to distinguish between normal and inverted neutrino mass orderings. Taking an exposure of?104?kg?yr?and a background rate of?10?4?counts/(keV?kg?yr), we find that a moderate evidence for normal neutrino mass ordering (i.e., with a Bayes factor?B?given by?ln(B)?2.5?or a probability about?92.3%?according to the Jeffreys scale) can be achieved if the true value of effective neutrino mass?mββ?turns out to be below?0.01?eV. |

Electromagnetic neutrinos in laboratory experiments and astrophysics

Carlo Giunti; Konstantin A. Kouzakov; Yu-Feng Li; Alexey V. Lokhov; Alexander I. Studenikin; Shun ZhouSubjects: Physics >> Nuclear Physics

An overview of neutrino electromagnetic properties, which open a door to the new physics beyond the Standard Model, is given. The effects of neutrino electromagnetic interactions both in terrestrial experiments and in astrophysical environments are discussed. The experimental bounds on neutrino electromagnetic characteristics are summarized. Future astrophysical probes of electromagnetic neutrinos are outlined. |

Subjects: Physics >> Nuclear Physics

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, 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. |

Supernova Bounds on keV-mass Sterile Neutrinos

Shun ZhouSubjects: Physics >> Nuclear Physics

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. |