arXiv subjects

Zhen-hua Zhao

Publications and source records attributed to Zhen-hua Zhao.

At least 37 records · Page 2Linked to original sources

arXiv2022

Simiplified textures of the seesaw model for the trimaximal neutrino mixings

In the seesaw framework, in the basis of $M^{}_{\rm R}$ being diagonal, we explore the simplified textures of $M^{}_{\rm D}$ that can naturally yield the trimaximal neutrino mixings and their consequences for the neutrino parameters and leptogenesis. We first formulate the generic textures of $M^{}_{\rm D}$ that can naturally yield the trimaximal mixings and then examine if their parameters can be further reduced. Our analysis is restricted to the simple but instructive scenario that there is only one phase parameter $ϕ$ responsible for both the CP violating effects at low energies and leptogenesis. Our attention is paid to the textures of $M^{}_{\rm D}$ that possess some vanishing or equal elements. On the basis of these results, we further examine if $ϕ$ can also take a particular value. The consequences of the phenomenologically-viable simplified textures for the neutrino parameters and leptogenesis are studied. A concrete flavor-symmetry model that can realize one representation of them is given.

hep-ph↗

arXiv2021

Renormalization group evolution induced leptogenesis in the minimal seesaw model with the trimaximal mixing and mu-tau reflection symmetry

In this paper, we consider the imbedding of the popular and well-motivated trimaximal mixing and $μ$-$τ$ reflection symmetry (which can help us shape the forms of the neutrino mass matrix) in the minimal seesaw model (which contains much fewer parameters than the general seesaw model) with two TeV-scale right-handed neutrinos (for realizing a low-scale seesaw) of nearly degenerate masses (for realizing a resonant leptogenesis). However, either for the trimaximal mixing scenario (which is realized through the Form Dominance approach here) or for the $μ$-$τ$ reflection symmetry scenario, leptogenesis cannot proceed. To address this issue, we consider the possibility that the special forms of the neutrino mass matrix for the trimaximal mixing and $μ$-$τ$ reflection symmetry are slightly broken by the renormalization group evolution effect, thus allowing leptogenesis to proceed. It is found that in the normal case of the neutrino mass ordering, the baryon asymmetry thus generated can reproduce the observed value. For completeness, we have also extended our analysis to the scenario that two right-handed neutrinos are not nearly degenerate any more. Unfortunately, in this scenario the final baryon asymmetry is smaller than the observed value by several orders of magnitude.

hep-ph↗

arXiv2021

The minimal seesaw and leptogenesis models

Given its briefness and predictability, the minimal seesaw -- a simplified version of the canonical seesaw mechanism with only two right-handed neutrino fields -- has been studied in depth and from many perspectives, and now it is being pushed close to a position of directly facing experimental tests. This article is intended to provide an up-to-date review of various phenomenological aspects of the minimal seesaw and its associated leptogenesis mechanism in neutrino physics and cosmology. Our focus is on possible flavor structures of such benchmark seesaw and leptogenesis scenarios and confronting their predictions with current neutrino oscillation data and cosmological observations. In this connection particular attention will be paid to the topics of lepton number violation, lepton flavor violation, discrete flavor symmetries, CP violation and antimatter of the Universe.

hep-ph↗

arXiv2019

Towards the meV limit of the effective neutrino mass in neutrinoless double-beta decays

In this paper, we emphasize why it is important for future neutrinoless double-beta ($0νββ$) decay experiments to reach the sensitivity to the effective neutrino mass $|m^{}_{ββ}| \approx 1~{\rm meV}$. Assuming such a sensitivity and the precisions on neutrino oscillation parameters after the JUNO experiment, we fully explore the constrained regions of the lightest neutrino mass $m^{}_1$ and two Majorana-type CP-violating phases $\{ρ, σ\}$. The implications for the neutrino mass spectrum, the effective neutrino mass $m^{}_β$ in beta decays and the sum of three neutrino masses $Σ\equiv m^{}_1 + m^{}_2 + m^{}_3$ relevant for cosmological observations are also discussed.

hep-ph↗

arXiv2019

Further study on the textures of neutrino mass matrix for maximal atmospherical mixing angle and Dirac CP phase

In this paper, we derive in a novel approach the possible textures of neutrino mass matrix that can lead to maximal atmospherical mixing angle ($θ^{}_{23} = π/4$) and Dirac CP phase ($δ= - π/2$) in two phenomenologically appealing scenarios: (1) one neutrino mass matrix element being vanishing (2) one neutrino mass being vanishing. For the obtained textures, some neutrino mass sum rules which relate the neutrino masses and mixing parameters will emerge. With the help of these sum rules, the unknown absolute neutrino mass scale and Majorana CP phases can be determined. Some discussions about the possible textures of neutrino mass matrix that can lead to $θ^{}_{23} = π/4$, $δ= - π/2$ and maximal Majorana CP phases ($ρ, σ= π/4$ or $3π/4$) as well as the model realization and breakings of the obtained textures are also given.

hep-ph↗

arXiv2018

On the textures of neutrino mass matrix for maximal atmospheric mixing angle and Dirac CP phase

In this paper, we derive in a novel approach the possible textures of neutrino mass matrix that can lead us to maximal atmospheric mixing angle and Dirac CP phase which are consistent with the current neutrino oscillation data. A total of eleven textures are thus found. Interestingly, the specific texture given by the $μ$-$τ$ reflection symmetry can be reproduced from one of the obtained textures. For these textures, some neutrino mass sum rules which relate the neutrino masses and Majorana CP phases will emerge.

hep-ph↗

arXiv2018

Modifications to the neutrino mixing from the mu-tau reflection symmetry

The $μ$-$τ$ reflection symmetry serves as a unique basis for understanding the observed neutrino mixing as it can lead us to the interesting results $θ^{}_{23} = π/4$ and $δ= -π/2$ which stand close to the current experimental results. But a precise measurement for $θ^{}_{23}$ and $δ$ will probably force us to modify the neutrino mixing $U^{(0)}$ from such a symmetry. Here we perform a study for modifications to $U^{(0)}$ in the forms of $U^{(1)\dagger} U^{(0)}$ and $U^{(0)} U^{(1)}$ where $U^{(1)}= R^{(1)}_{ij}$ (for $ij = 12, 23$ and 13) with $R^{(1)}_{ij}$ denoting a real orthogonal rotation on the $ij$ plane.

hep-ph↗

arXiv2017

Neutrino mu-tau reflection symmetry and its breaking in the minimal seesaw

In this paper, we attempt to implement the neutrino $μ$-$τ$ reflection symmetry (which predicts $θ^{}_{23} = π/4$ and $δ= \pm π/2$ as well as trivial Majorana phases) in the minimal seesaw (which enables us to fix the neutrino masses). For some direct (the preliminary experimental hints towards $θ^{}_{23} \neq π/4$ and $δ\neq - π/2$) and indirect (inclusion of the renormalization group equation effect and implementation of the leptogenesis mechanism) reasons, we particularly study the breakings of this symmetry and their phenomenological consequences.

hep-ph↗

arXiv2017

Breakings of the neutrino mu-tau reflection symmetry

The neutrino $μ$-$τ$ reflection symmetry has been attracting a lot of attention as it predicts the interesting results $θ^{}_{23} = π/4$ and $δ= \pm π/2$. But it is reasonable to consider breakings of such a symmetry either from the theoretical considerations or on the basis of experimental results. We thus perform a systematic study for the possible symmetry-breaking patterns and their implications for the mixing parameters. The general treatment is applied to some specific symmetry breaking arising from the renormalization group effects for illustration.

hep-ph↗

arXiv2017

The effective neutrino mass of neutrinoless double-beta decays: how possible to fall into a well

If massive neutrinos are the Majorana particles and have a normal mass ordering, the effective mass term $\langle m\rangle^{}_{ee}$ of a neutrinoless double-beta ($0ν2β$) decay may suffer significant cancellations among its three components and thus sink into a decline, resulting in a "well" in the three-dimensional graph of $|\langle m\rangle^{}_{ee}|$ against the smallest neutrino mass $m^{}_1$ and the relevant Majorana phase $ρ$. We present a new and complete analytical understanding of the fine issues inside such a well, and discover a novel threshold of $|\langle m\rangle^{}_{ee}|$ in terms of the neutrino masses and flavor mixing angles: $|\langle m\rangle^{}_{ee}|^{}_* = m^{}_3 \sin^2θ^{}_{13}$ in connection with $\tanθ^{}_{12} = \sqrt{m^{}_1/m^{}_2}$ and $ρ=π$. This threshold point, which links the {\it local} minimum and maximum of $|\langle m\rangle^{}_{ee}|$, can be used to signify observability or sensitivity of the future $0ν2β$-decay experiments. Given current neutrino oscillation data, the possibility of $|\langle m\rangle^{}_{ee}| < |\langle m\rangle^{}_{ee}|^{}_*$ is found to be very small.

hep-ph↗

arXiv2016

750 GeV diphoton excess confronted with a top-pion in the TTM model

The latest LHC data suggest an intriguing excess at $m_{γγ} = 750$ GeV which apparently requires an explanation from the beyond standard model physics. In this note we explore the possibility for this signal to arise from a top-pion in the Top Triangle Moose model which can be viewed as a dimensional-deconstruction version of the top-color assisted technicolor model. We demonstrate that the observed excess can be accommodated by and has important implications for this interesting model.

hep-ph↗

arXiv2016

On the breaking of mu-tau flavor symmetry

In light of the observation of a relatively large $θ^{}_{13}$, one has to consider breaking the $μ$-$τ$ symmetry properly which would otherwise result in a vanishing $θ^{}_{13}$ (as well as $θ^{}_{23} = π/4$). Therefore, we investigate various symmetry-breaking patterns and accordingly identify those that are phenomenologically viable. Furthermore, the symmetry-breaking effects arising from some specific physics (e.g., the renormalization group equation running effect) are discussed as well.

hep-ph↗

arXiv2016

A review of mu-tau flavor symmetry in neutrino physics

Behind the observed pattern of lepton flavor mixing is a partial or approximate mu-tau flavor symmetry --- a milestone on our road to the true origin of neutrino masses and flavor structures. In this review article we first describe the features of mu-tau permutation and reflection symmetries, and then explore their various consequences on model building and neutrino phenomenology. We pay particular attention to soft mu-tau symmetry breaking, which is crucial for our deeper understanding of the fine effects of flavor mixing and CP violation.

hep-ph↗

arXiv2015

A modified Friedberg-Lee symmetry for the TM1 neutrino mixing

In this letter, we put forward a special neutrino mass matrix which is invariant under a modified Friedberg-Lee (FL) transformation $ν^{}_e \to ν^{}_e-2θ$ and $ν^{}_{μ, τ} \to ν^{}_{μ, τ}+θ$ with $θ$ being a space-time independent element of the Grassmann algebra. Compared to the original FL symmetry (with the transformation $ν^{}_{e, μ, τ} \to ν^{}_{e, μ, τ}+θ$) which results in the TM2 neutrino mixing, the modified FL symmetry will lead us to the TM1 mixing which has a better agreement with the experimental results. While the original FL symmetry has to be broken in order to produce a realistic neutrino mass spectrum, the modified FL symmetry is allowed to remain intact and give us a vanishing $m^{}_1$. A combination of the FL symmetry with the $μ$-$τ$ reflection symmetry is also discussed.

hep-ph↗

arXiv2015

On the four-zero texture of quark mass matrices and its stability

We carry out a new study of quark mass matrices $M^{}_{\rm u}$ (up-type) and $M^{}_{\rm d}$ (down-type) which are Hermitian and have four zero entries, and find a new part of the parameter space which was missed in the previous works. We identify two more specific four-zero patterns of $M^{}_{\rm u}$ and $M^{}_{\rm d}$ with fewer free parameters, and present two toy flavor-symmetry models which can help realize such special and interesting quark flavor structures. We also show that the texture zeros of $M^{}_{\rm u}$ and $M^{}_{\rm d}$ are essentially stable against the evolution of energy scales in an analytical way by using the one-loop renormalization-group equations.

hep-ph↗

arXiv2015

How to interpret a discovery or null result of the $0ν2β$ decay

The Majorana nature of massive neutrinos will be crucially probed in the next-generation experiments of the neutrinoless double-beta ($0ν2β$) decay. The effective mass term of this process, $\langle m\rangle^{}_{ee}$, may be contaminated by new physics. So how to interpret a discovery or null result of the $0ν2β$ decay in the foreseeable future is highly nontrivial. In this paper we introduce a novel three-dimensional description of $|\langle m\rangle_{ee}^{}|$, which allows us to see its sensitivity to the lightest neutrino mass and two Majorana phases in a transparent way. We take a look at to what extent the free parameters of $|\langle m\rangle_{ee}^{}|$ can be well constrained provided a signal of the $0ν2β$ decay is observed someday. To fully explore lepton number violation, all the six effective Majorana mass terms $\langle m\rangle_{αβ}^{}$ (for $α, β= e, μ, τ$) are calculated and their lower bounds are illustrated with the two-dimensional contour figures. The effect of possible new physics on the $0ν2β$ decay is also discussed in a model-independent way. We find that the result of $|\langle m\rangle_{ee}^{}|$ in the normal (or inverted) neutrino mass ordering case modified by the new physics effect may somewhat mimic that in the inverted (or normal) mass ordering case in the standard three-flavor scheme. Hence a proper interpretation of a discovery or null result of the $0ν2β$ decay may demand extra information from some other measurements.

hep-ph↗

arXiv2014

Minimal modifications to the Tri-Bimaximal neutrino mixing

In light of the observation of a relatively large $θ_{13}$, the ever popular Tri-Bimaximal (TBM) neutrino mixing which predicts a vanishing $θ_{13}$ needs modifications. In this paper, we shall discuss the possibility of modifying it in a minimal way to fulfil this task. In the first part, a neutrino mass matrix with three independent parameters, which leads to the TM2 mixing, is obtained by analogy with that for the TBM mixing. In the second part, a model that can realize the TM2 mixing is constructed with flavor symmetries $A_4 \times U(1) \times Z_2 \times Z_2 \times Z_2$. It is the variant of a model that gives the TBM mixing, with only one more flavon field included. Furthermore, the imaginary vacuum expectation value (VEV) of this flavon breaks the imposed CP symmetry and results in $θ_{23}=45^\circ$ and the maximal CP violation. This VEV is also helpful for providing a large enough CP asymmetry required by the leptogenesis mechanism. Besides, this model building approach can be generalized to the TM1 mixing in a straightforward way.

hep-ph↗

arXiv2014

Tests of Lorentz and CPT Violation in the Medium Baseline Reactor Antineutrino Experiment

Tests of Lorentz and CPT violation in the medium baseline reactor antineutrino experiment are presented in the framework of the Standard Model Extension (SME). Both the spectral distortion and sidereal variation are employed to derive the limits of Lorentz violation (LV) coefficients. We do the numerical analysis of the sensitivity of LV coefficients by taking the Jiangmen Underground Neutrino Observatory (JUNO) as an illustration, which can improve the sensitivity by more than two orders of magnitude compared with the current limits from reactor antineutrino experiments.

hep-ph↗