arXiv subjects
Publications and source records attributed to Zhi-zhong Xing.
We calculate the rephasing invariants of CP and T violation in a favorable parametrization of the 4x4 lepton flavor mixing matrix. Their relations with the CP- and T-violating asymmetries in neutrino oscillations are derived, and the matter effects are briefly discussed.
We present a concise formula to relate the effective mass term of the neutrinoless double beta decay to a single neutrino mass, two Majorana CP-violating phases and four observables of neutrino oscillations for a generic neutrino mass spectrum. If the alleged evidence for the neutrinoless double beta decay is taken into account, one may obtain a rough but model-independent constraint on the absolute scale of neutrino masses -- it is most likely to be in the range between 0.1 eV and 1 eV.
We make an analysis of the fake CPT-violating asymmetries between the survival probabilities of neutrinos and antineutrinos, induced by the terrestrial matter effects, in three different scenarios of long-baseline neutrino oscillation experiments with L=730 km, L=2100 km and L=3200 km. In particular, the dependence of those asymmetries on the Dirac-type CP-violating phase of the lepton flavor mixing matrix is examined.
We argue that a small or large CP-violating asymmetry {\cal A}_{ψK_S} in B^0_d vs \bar{B}^0_d --> J/ψK_S decays, which seems to be favored by the recent BaBar or Belle data, might hint at the existence of new physics in B^0_d - \bar{B}^0_d mixing. We present a model-independent framework to show how new physics in B^0_d - \bar{B}^0_d mixing modifies the standard-model CP-violating asymmetry {\cal A}^{\rm SM}_{ψK_S}. We particularly emphasize that an experimental confirmation of {\cal A}_{ψK_S} \approx {\cal A}^{\rm SM}_{ψK_S} must not imply the absence of new physics in B^0_d - \bar{B}^0_d mixing.
I follow a lesson learnt from Heisenberg's matrix Quantum Mechanics to study the property of lepton flavor mixing and CP violation. I show that the commutator of lepton mass matrices defined in vacuum keeps invariant under terrestrial matter effects within the four-neutrino mixing scheme. A set of model-independent sum rules for neutrino masses are obtained, and they can be generalized to hold for an arbitrary number of neutrino families. Useful sum rules for the rephasing-invariant measures of leptonic CP violation have also been found. Finally I present a generic formula of T-violating asymmetries applicable to the future long-baseline neutrino oscillation experiments.
The first observation of the color-suppressed decay mode \bar{B}^0_d --> D^(*)0 π^0 by the Belle and CLEO Collaborations makes a quantitative analysis of the isospin relations for the amplitudes of B --> D^(*)πpossible. The strong (isospin) phase difference in B --> Dπtransitions is found to be about 29^\circ by use the Belle data or 26^\circ by use of the CLEO data, implying that final-state interactions might not be negligible. Applying the factorization approximation to I=3/2 and I=1/2 isospin amplitudes of B --> Dπdecays, we obtain the ratio of the effective Wilson coefficients a^{eff}_1 and a^{eff}_2: a^{eff}_2/a^{eff}_1 \approx 0.27. A similar analysis shows that the magnitude of final-state interactions in B --> D^*πmight be comparable with that in B --> Dπ, and the factorization hypothesis works consistently in both of them.
We present a classification of possible parametrizations of the 3x3 lepton flavor mixing matrix in terms of the rotation and phase angles. A particular parametrization, which is most convenient to describe the observables of neutrino oscillations and that of the neutrinoless double beta decay, is studied in detail. The possibility to determine the Dirac- and Majorana-type CP-violating phases are also discussed.
We point out the simple reversibility between the fundamental neutrino mixing parameters in vacuum and their effective counterparts in matter. The former can therefore be expressed in terms of the latter, allowing more straightforward extraction of the genuine lepton mixing quantities from a variety of long-baseline neutrino oscillation experiments. In addition to the parametrization-independent results, we present the formulas based on the standard parametrization of the lepton flavor mixing matrix and give a typical numerical illustration.
We point out two simple but instructive possibilities to construct the charged lepton and neutrino mass matrices, from which the nearly bi-maximal neutrino mixing with large T violation can naturally emerge. The two lepton mixing scenarios are compatible very well with current experimental data on solar and atmospheric neutrino oscillations, and one of them may lead to an observable T-violating asymmetry between ν_μ--> ν_e and ν_e --> ν_μtransitions in the long-baseline neutrino oscillation experiments. Their implications on the neutrinoless double beta decay are also discussed.
We show that the commutator of lepton mass matrices is invariant under terrestial matter effects in the four-neutrino mixing scheme. A set of model-independent sum rules for neutrino masses, which may be generalized to hold for an arbitrary number of neutrino families, are for the first time uncovered. Useful sum rules for the rephasing-invariant measures of leptonic CP violation have also been found. Finally we present a generic formula of T-violating asymmetries and expect it to be applicable to the future long-baseline neutrino oscillation experiments.
We interpret the newly observed muon g-2 anomaly in the framework of a leptonic Higgs doublet model with nearly degenerate neutrino masses and nearly bi-maximal neutrino mixing. Useful constraints are obtained on the rates of lepton-flavor-violating rare decays $τ\to μγ$, $μ\to e γ$ and $τ\to e γ$ as well as the $μ$-$e$ conversion ratio $R_{μe}$. We find that $Γ(μ\to e γ)$, $Γ(τ\to e γ)$ and $R_{μe}$ depend crucially on possible non-zero but samll values of the neutrino mixing matrix element $V_{e3}$, and they are also sensitive to the Dirac-type CP-violating phase. In particular, we show that $Γ(τ\to μγ)/m^5_τ$, $Γ(μ\to e γ)/m^5_μ$ and $Γ(τ\to e γ)/m^5_τ$ are approximately in the ratio $1: 2|V_{e3}|^2: 2|V_{e3}|^2$ if $|V_{e3}|$ is much larger than ${\cal O}(10^{-2})$, and in the ratio $2 (Δm^2_{\rm atm})^2: (Δm^2_{\rm sun})^2:(Δm^2_{\rm sun})^2$ if $|V_{e3}|$ is much lower than ${\cal O}(10^{-3})$, where $Δm^2_{\rm atm}$ and $Δm^2_{\rm sun}$ are the corresponding mass-squared differences of atmospheric and solar neutrino oscillations.
With the help of the light-quark triangle, which is essentially congruent to the rescaled unitarity triangle for a variety of textures of the quark mass matrices, we calculate the CP-violating quantity \sin 2βand the ratio of |V_{ub}| to |V_{cb}|. We find that \sin 2βis most likely to lie in the range 0.45 \leq \sin 2β\leq 0.60, a result compatible very well with the present BaBar and Belle measurements. On the other hand, |V_{ub}/V_{cb}| \geq 0.8 is disfavored. Our bounds on both \sin 2βand |V_{ub}/V_{cb}| can soon be confronted with more precise data to be accumulated from the asymmetric B-meson factories.
The renormalization effect on a specific ansatz of lepton mass matrices, arising naturally from the breaking of flavor democracy for charged leptons and that of mass degeneracy for light neutrinos, is studied from a superhigh energy scale M_0 \sim 10^{13} GeV to the electroweak scale in the framework of the minimal supersymmetric standard model. We find that the democratic neutrino mixing pattern obtained from this ansatz may in general be instable against radiative corrections. With the help of similar flavor symmetries we prescribe a slightly different scheme of lepton mass matrices at the scale M_0, from which the democratic mixing pattern of lepton flavors can be achieved, after radiative corrections, at the experimentally accessible scales.
We introduce the commutators of lepton mass matrices to describe the phenomenon of lepton flavor mixing, and establish their relations to the effective Hamiltonians responsible for the propagation of Dirac and Majorana neutrinos. The determinants of those commutators are invariant under matter effects, leading to an instructive relationship between the universal CP-violating parameters in vacuum and in matter. In the scenario of low-energy (100 MeV \leq E \leq 1 GeV) and medium-baseline (100 km \leq L \leq 400 km) neutrino experiments, we illustrate the features of lepton flavor mixing and CP violation. The terrestrial matter effects on CP- and T-violating asymmetries in ν_μ\to ν_e and $\barν_μ\to \barν_e neutrino oscillations are also discussed. We demonstrate that a relatively pure signal of leptonic CP violation at the percent level can be established from such medium-baseline experiments with low-energy neutrino beams.
The significance of final-state interactions in B_d-->ππdecays is phenomenologically demonstrated by taking elastic ππ--ππand inelastic ππ--D\bar{D} rescattering effects into consideration. We find that the present experimental data on B^0_d-->π^+π^- can well be understood in this approach without fine-tuning of the input parameters, and large CP-violating asymmetries are expected to manifest themselves in such charmless rare processes.
Within the framework of three lepton families we have derived an exact and compact formula to describe the matter effect on neutrino mixing and CP violation. This model- and parametrization-independent result can be particularly useful for recasting the fundamental lepton flavor mixing matrix from a variety of long-baseline neutrino experiments.
Within the framework of three lepton families I present a transparent analytical relationship between the neutrino mixing and CP-violating parameters in vacuum and thos in matter. Such a model- and parametrization-independent result will be particularly useful to recast the fundamental lepton flavor mixing matrix from the future long-baseline neutrino experiments.
We show that the CP-violating effect in K^0 vs \bar K^0-->π^+π^-π^0 decays differs from that in K_{\rm L}-->π^+π^-, K_{\rm L}-->π^0π^0 or the semileptonic K_{\rm L} transitions, if there exists CPT violation in K^0-\bar{K}^0 mixing. A delicate measurement of this difference in the KTeV experiment and at the ϕfactory will provide a new test of CPT symmetry in the neutral kaon system.