• Discriminating between Thermal and Nonthermal Cosmic Relic Neutrinos through Annual Modulation at PTOLEMY

    分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10

    摘要: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

    分类: 物理学 >> 核物理学 提交时间: 2016-09-20

    摘要: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

    分类: 物理学 >> 核物理学 提交时间: 2016-09-19

    摘要: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

    分类: 物理学 >> 核物理学 提交时间: 2016-09-14

    摘要: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.

  • Update on two-zero textures of the Majorana neutrino mass matrix in light of recent T2K, Super-Kamiokande and NO$\nu$A results

    分类: 物理学 >> 核物理学 提交时间: 2016-09-14

    摘要:The latest results from atmospheric and accelerator neutrino experiments indicate that the normal neutrino mass ordering m145∘ are favored. In light of new experimental results, we update previous phenomenological studies on two-zero textures of the Majorana neutrino mass matrix Mν, in the flavor basis where the charged-lepton mass matrix Ml is diagonal. When the 1σ ranges of neutrino mixing parameters are taken into account, only four (i.e., A1,2 and B2,4) among seven two-zero patterns of Mν show the aforementioned features of neutrino mass spectrum, mixing angle θ23 and CP-violating phase δ, and thus are compatible with the latest neutrino oscillation data. The correlative relations among neutrino masses and mixing parameters have been derived analytically for these four patterns, and the allowed regions of neutrino mixing angles and the CP-violating phase are also given. Possible realizations of four viable two-zero textures via non-Abelian discrete flavor symmetries are discussed.

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

    分类: 物理学 >> 核物理学 提交时间: 2016-09-14

    摘要: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.

  • Determination of neutrino mass ordering in future $^76$Ge-based neutrinoless double-beta decay experiments

    分类: 物理学 >> 核物理学 提交时间: 2016-09-14

    摘要: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

    分类: 物理学 >> 核物理学 提交时间: 2016-09-13

    摘要: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.

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

    分类: 物理学 >> 核物理学 提交时间: 2016-09-13

    摘要: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

    分类: 物理学 >> 核物理学 提交时间: 2016-09-13

    摘要: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.

  • Majorana Neutrino Masses from Neutrinoless Double-Beta Decays and Lepton-Number-Violating Meson Decays

    分类: 物理学 >> 核物理学 提交时间: 2016-09-06

    摘要:The Schechter-Valle theorem states that a positive observation of neutrinoless double-beta (0νββ) decays implies a finite Majorana mass term for neutrinos when any unlikely fine-tuning or cancellation is absent. In this note, we reexamine the quantitative impact of the Schechter-Valle theorem, and find that current experimental lower limits on the half-lives of 0νββ-decaying nuclei have placed a restrictive upper bound on the Majorana neutrino mass |δmeeν|<7.43×10−29 eV radiatively generated at the four-loop level. Furthermore, we generalize this quantitative analysis of 0νββ decays to that of the lepton-number-violating (LNV) meson decays M−→M′++ℓ−α+ℓ−β (for α, β = e or μ). Given the present upper limits on these rare LNV decays, we have derived the loop-induced Majorana neutrino masses |δmeeν|<9.7×10−18 eV, |δmeμν|<1.6×10−15 eV and |δmμμν|<1.0×10−12 eV from K−→π++e−+e−, K−→π++e−+μ− and K−→π++μ−+μ−, respectively. A partial list of radiative neutrino masses from the LNV decays of D, Ds and B mesons is also given.

  • Getting the Most from Detection of Galactic Supernova Neutrinos in Future Large Liquid-Scintillator Detectors

    分类: 物理学 >> 核物理学 提交时间: 2016-09-05

    摘要:Future large liquid-scintillator detectors can be implemented to observe neutrinos from a core-collapse supernova (SN) in our galaxy in various reaction channels: (1) The inverse beta decay ν¯¯¯e+p→n+e+; (2) The elastic neutrino-proton scattering ν+p→ν+p; (3) The elastic neutrino-electron scattering ν+e−→ν+e−; (4) The charged-current νe interaction νe+12C→e−+12N; (5) The charged-current ν¯¯¯e interaction ν¯¯¯e+12C→e++12B; (6) The neutral-current interaction ν+12C→ν+12C∗. The less abundant 13C atoms in the liquid scintillator are also considered as a target, and both the charged-current interaction νe+13C→e−+13N and the neutral-current interaction ν+13C→ν+13C∗ are taken into account. In this work, we show for the first time that a global analysis of all these channels at a single {liquid-}scintillator detector, such as Jiangmen Underground Neutrino Observatory (JUNO), is very important to test the average-energy hierarchy of SN neutrinos and how the total energy is partitioned among neutrino flavors. In addition, the dominant channels for reconstructing neutrino spectra and the impact of other channels are discussed in great detail.

  • Radiative Corrections to the Sum Rule of Lepton Flavor Mixing

    分类: 物理学 >> 核物理学 提交时间: 2016-09-01

    摘要:The simple correlation among three lepton flavor mixing angles (θ12,θ13,θ23) and the leptonic Dirac CP-violating phase δ is conventionally called a sum rule of lepton flavor mixing, which may be derived from a class of neutrino mass models with flavor symmetries. In this paper, we consider the sum rule θ12≈θν12+θ13cosδ, where θν12 stems from a constant mixing pattern in the neutrino sector and takes the value of θν12=45∘ for the bi-maximal mixing (BM), θν12=35.3∘ for the tri-bimaximal mixing (TBM) or θν12=tan−1[2/(5√+1)]≈31.7∘ for the golden-ratio mixing (GR), and investigate the renormalization-group (RG) running effects on lepton flavor mixing parameters when this sum rule is assumed at a superhigh-energy scale. Quantitatively, we implement the Bayesian approach to explore the posterior distribution of δ at the low-energy scale, which becomes quite broad when the RG running effects are significant, as in the minimal supersymmetric standard model (MSSM) with a sizeable value of tanβ. Moreover, we also discuss the compatibility of the above three mixing scenarios with current neutrino oscillation data, and observe that radiative corrections can increase such a compatibility for the BM scenario, resulting in a weaker preference for the TBM and GR ones.