arXiv subjects

Zhi-zhong Xing

Publications and source records attributed to Zhi-zhong Xing.

At least 163 records · Page 9Linked to original sources

arXiv2005

Leptonic Unitarity Triangles in Matter

We present a geometric description of lepton flavor mixing and CP violation in matter by using the language of leptonic unitarity triangles. The exact analytical relations for both sides and inner angles are established between every unitarity triangle in vacuum and its effective counterpart in matter. The typical shape evolution of six triangles with the terrestrial matter density is illustrated for a realistic long-baseline neutrino oscillation experiment.

hep-ph↗

arXiv2005

Model-independent Constraints on the Weak Phase $α$ (or $ϕ_2$) and QCD Penguin Pollution in $B \to ππ$ Decays

We present an {\it algebraic} isospin approach towards a more straightforward and model-independent determination of the weak phase $α$ (or $ϕ_2$) and QCD penguin pollution in $B\to ππ$ decays. The world averages of current experimental data allow us to impose some useful constraints on the isospin parameters of $B\to ππ$ transitions. We find that the magnitude of $α$ (or $ϕ_2$) extracted from the indirect CP violation in $π^+π^-$ mode is in agreement with the standard-model expectation from other indirect measurements, but its four-fold discrete ambiguity has to be resolved in the near future.

hep-ph↗

arXiv2004

Flavor Mixing and CP Violation of Massive Neutrinos

We present an overview of recent progress in the phenomenological study of neutrino masses, lepton flavor mixing and CP violation. We concentrate on the model-independent properties of massive neutrinos, both in vacuum and in matter. Current experimental constraints on the neutrino mass spectrum and the lepton flavor mixing parameters are summarized. The Dirac- and Majorana-like phases of CP violation, which are associated respectively with the long-baseline neutrino oscillations and the neutrinoless double beta decay, are discussed in detail. The seesaw mechanism, the leptogenesis scenario and the strategies to construct lepton mass matrices are briefly described. The features of flavor mixing between one sterile neutrino and three active neutrinos are also explored.

hep-ph↗

arXiv2004

Seesaw Invariance of Fritzsch-like Neutrino Mass Matrices, Leptogenesis and Lepton Flavor Violation

We propose a simple ansatz for neutrino phenomenology, in which the relevant lepton mass matrices take the universal Fritzsch-like form and the seesaw relation holds under a particular condition. There exist six textures of this nature, but their consequences on neutrino oscillations are exactly the same. We show that our scenario is viable to account for the cosmological baryon number asymmetry via thermal leptogenesis. Its predictions for the lepton-flavor-violating decays μ-> eγ, tau -> μγand τ-> eγare also presented. We find that the branching ratios of these rare processes depend strongly upon the phase parameters responsible for leptogenesis and for leptonic CP violation in neutrino oscillations.

hep-ph↗

arXiv2004

A Systematic Study of Neutrino Mixing and CP Violation from Lepton Mass Matrices with Six Texture Zeros

We present a systematic study of 400 combinations of the charged lepton and neutrino mass matrices with six vanishing entries or texture zeros. Only 24 of them, which can be classified into a few distinct categories, are found to be compatible with current neutrino oscillation data at the $3σ$ level. A peculiar feature of the lepton mass matrices in each category is that they have the same phenomenological consequences. Taking account of a simple seesaw scenario for six parallel patterns of the charged lepton and Dirac neutrino mass matrices with six zeros, we show that it is possible to fit the experimental data at or below the $2σ$ level. In particular, the maximal atmospheric neutrino mixing can be reconciled with a strong neutrino mass hierarchy in the seesaw case. Numerical predictions are also obtained for the neutrino mass spectrum, flavor mixing angles, CP-violating phases and effective masses of the tritium beta decay and the neutrinoless double beta decay.

hep-ph↗

arXiv2004

Universal Neutrino Mass Hierarchy and Cosmological Baryon Number Asymmetry

We conjecture that three light Majorana neutrinos and their right-handed counterparts may have a universal geometric mass hierarchy. Incorporating this phenomenological conjecture with the Fritzsch texture of lepton mass matrices in a simple seesaw mechanism, we show that it is possible to simultaneously account for current neutrino oscillation data and the cosmological baryon number asymmetry via leptogenesis.

hep-ph↗

arXiv2004

Flavor Democracy and Type-II Seesaw Realization of Bilarge Neutrino Mixing

We generalize the democratic neutrino mixing Ansatz by incorporating the type-II seesaw mechanism with S(3) flavor symmetry. We find that bilarge neutrino mixing can naturally appear if the flavor democracy contribution is strongly suppressed due to significant cancellation between the conventional seesaw and triplet mass terms. Explicit S(3) symmetry breaking yields successful neutrino phenomenology and various testable correlations between the neutrino mass and mixing parameters. Among the results are a normal neutrino mass ordering, $0.005 \le |U_{e3}| \le 0.057$, $1 - \sin^2 2θ_{23} \ge 0.005$, positive $J_{\rm CP}$ and moderate cancellation in the effective mass of the neutrinoless double beta decay.

hep-ph↗

arXiv2004

Radiative Generation of $θ_{13}$ with the Seesaw Threshold Effect

We examine whether an appreciable value of the lepton flavor mixing angle $θ_{13}$ at the electroweak scale $Λ_{\rm EW}$ can be radiatively generated from $θ_{13} = 0^\circ$ at the GUT scale $Λ_{\rm GUT}$. It is found that the renormalization-group running and seesaw threshold effects may lead to $θ_{13} \sim 5^\circ$ at low energies for two simple large-maximal mixing patterns of the MNS matrix in the minimal supersymmetric standard model. If $θ_{12}$ is sufficiently large at $Λ_{\rm GUT}$, it will be possible to radiatively produce $θ_{13} \sim 5^\circ$ at $Λ_{\rm EW}$ both in the standard model and in its supersymmetric extensions. The mass spectrum of three heavy right-handed Majorana neutrinos and the cosmological baryon number asymmetry via leptogenesis are also calculated.

hep-ph↗

arXiv2004

Democratic Neutrino Mixing Reexamined

We reexamine the democratic neutrino mixing ansatz, in which the mass matrices of charged leptons and Majorana neutrinos arise respectively from the explicit breaking of S(3)_L x S(3)_R and S(3) flavor symmetries. It is shown that a democracy term in the neutrino sector can naturally allow the ansatz to fit the solar neutrino mixing angle θ_sun \approx 33^\circ. We predict \sin^2 2θ_atm \approx 0.95 for atmospheric neutrino mixing and J \approx 1.2% for leptonic CP violation in neutrino oscillations without any fine-tuning. Direct relations between the model parameters and experimental observables are also discussed.

hep-ph↗

arXiv2004

Texture Zeros and CP-violating Phases in the Neutrino Mass Matrix

We stress that specific texture zeros of lepton mass matrices, which might dynamically arise from a new kind of flavor symmetry, can help us to establish simple and testable relations between the lepton flavor mixing parameters and lepton mass ratios. We present a brief review of one-zero, two-zero and three-zero textures of the neutrino mass matrix. Their phenomenological consequences on neutrino mixing and CP violation are also discussed.

hep-ph↗

arXiv2004

Isomeric Lepton Mass Matrices and Bi-large Neutrino Mixing

We show that there exist six parallel textures of the charged lepton and neutrino mass matrices with six vanishing entries, whose phenomenological consequences are exactly the same. These {\it isomeric} lepton mass matrices are compatible with current experimental data at the $3σ$ level. If the seesaw mechanism and the Fukugita-Tanimoto-Yanagida hypothesis are taken into account, it will be possible to fit the experimental data at or below the $2σ$ level. In particular, the maximal atmospheric neutrino mixing can be reconciled with a strong neutrino mass hierarchy in the seesaw case.

hep-ph↗

arXiv2003

Impact of Fermion Mass Degeneracy on Flavor Mixing

We carry out a systematic analysis of flavor mixing and CP violation in the conceptually interesting limit where two quarks or leptons of the same charge are degenerate in mass. We pay some particular attention to the impact of neutrino mass degeneracy and Majorana phase degeneracy on the lepton flavor mixing matrix.

hep-ph↗

arXiv2003

Radiative Corrections to Neutrino Mixing and CP Violation in the Minimal Seesaw Model with Leptogenesis

Radiative corrections to neutrino mixing and CP violation are analyzed in the minimal seesaw model with two heavy right-handed neutrinos. We find that textures of the effective Majorana neutrino mass matrix are essentially stable against renormalization effects. Taking account of the Frampton-Glashow-Yanagida ansatz for the Dirac neutrino Yukawa coupling matrix, we calculate the running effects of light neutrino masses, lepton flavor mixing angles and CP-violating phases for both $m_1 =0$ (normal mass hierarchy) and $m_3 =0$ (inverted mass hierarchy) cases in the standard model and in its minimal supersymmetric extension. Very instructive predictions for the cosmological baryon number asymmetry via thermal leptogenesis are also given with the help of low-energy neutrino mixing quantities.

hep-ph↗

arXiv2003

Calculable CP-violating Phases in the Minimal Seesaw Model of Leptogenesis and Neutrino Mixing

We show that all nontrivial CP-violating phases can be determined in terms of three lepton flavor mixing angles and the ratio of $Δm^2_{\rm sun}$ to $Δm^2_{\rm atm}$ in the minimal seesaw model in which the Frampton-Glashow-Yanagida (FGY) ansatz is incorporated. This important point allows us to make very specific predictions for the cosmological baryon number asymmetry and CP violation in neutrino oscillations. A measurement of the smallest neutrino mixing angle will sensitively test the FGY ansatz, in particular in the case that three light neutrinos have a normal mass hierarchy.

hep-ph↗

arXiv2003

Direct CP Violation and Isospin Triangles of B->ππDecays

The recent observation of B^0_d->π^0π^0 and \bar{B}^0_d->π^0π^0 decay modes allows us to make a fresh isospin analysis of B->ππtransitions. We find that current experimental data can impose some model-independent constraints on the parameter space of direct CP violation in B_d->π^+π^- and B_d->π^0π^0. Furthermore, we establish a direct relationship between the weak phase αand the charge-averaged branching fractions and CP-violating asymmetries of B->ππdecays.

hep-ph↗

arXiv2003

Complete Parameter Space of Quark Mass Matrices with Four Texture Zeros

The full parameter space of Hermitian quark mass matrices with four texture zeros is explored by using current experimental data. We find that all ten free parameters of the four-zero quark mass matrices can well be constrained. In particular, only one of the two phase parameters plays an important role in CP violation. The structural features of this specific pattern of quark mass matrices are also discussed in detail.

hep-ph↗

arXiv2003

Vanishing Effective Mass of the Neutrinoless Double Beta Decay?

We stress that massive neutrinos may be Majorana particles even if the effective mass of the neutrinoless double beta decay m_ee vanishes. We show that current neutrino oscillation data do allow m_ee = 0 to hold, if the Majorana CP-violating phases lie in two specific regions. Strong constraints on three neutrino masses can then be obtained. We find that the neutrino mass spectrum performs a normal hierarchy: m_1 < m_2 < m_3. A possible texture of the neutrino mass matrix is also illustrated under the m_ee = 0 condition.

hep-ph↗

arXiv2003

The Majorana Neutrino Mass Matrix with One Texture Zero and One Vanishing Eigenvalue

Possible patterns of the Majorana neutrino mass matrix $M$ with one texture zero and one vanishing eigenvalue are classified and discussed. We find that three one-zero textures of $M$ with $m_1 =0$ and four one-zero textures of $M$ with $m_3 =0$ are compatible with current neutrino oscillation data. The implications of these phenomenological ans$\rm\ddot{a}$tze on the neutrino mass spectrum and the neutrinoless double beta decay are also explored in some detail.

hep-ph↗