arXiv subjects

Ye-Ling Zhou

Publications and source records attributed to Ye-Ling Zhou.

70 records · Page 4Linked to original sources

arXiv2016

Flavon-induced connections between lepton flavour mixing and charged lepton flavour violation processes

In leptonic flavour models with discrete flavour symmetries, couplings between flavons and leptons can result in special flavour structures after they gain vacuum expectation values. At the same time, they can also contribute to the other lepton-flavour-violating processes. We study the flavon-induced LFV 3-body charged lepton decays and radiative decays and we take as example the $A_4$ discrete symmetry. In $A_4$ models, a $Z_3$ residual symmetry roughly holds in the charged lepton sector for the realisation of tri-bimaximal mixing at leading order. The only processes allowed by this symmetry are $τ^-\to μ^+ e^- e^-, e^+ μ^- μ^-$, and the other 3-body and all radiative decays are suppressed by small $Z_3$-breaking effects. These processes also depend on the representation the flavon is in, whether pseudo-real (case i) or complex (case ii). We calculate the decay rates for all processes for each case and derive their strong connection with lepton flavour mixing. In case i, sum rules for the branching ratios of these processes are obtained, with typical examples $\text{Br}(τ^-\to μ^+ e^- e^-) \approx \text{Br}(τ^-\to e^+ μ^- μ^-)$ and $\text{Br}(τ^-\to e^- γ) \approx \text{Br}(τ^-\to μ^- γ)$. In case ii, we observe that the mixing between two $Z_3$-covariant flavons plays an important role. All processes are suppressed by charged lepton masses and current experimental constraints allow the electroweak scale and the flavon masses to be around hundreds of GeV. Our discussion can be generalised in other flavour models with different flavour symmetries.

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arXiv2016

The role of flavon cross couplings in leptonic flavour mixing

In models with discrete flavour symmetries, flavons are critical to realise specific flavour structures. Leptonic flavour mixing originates from the misalignment of flavon vacuum expectation values which respect different residual symmetries in the charged lepton and neutrino sectors. Flavon cross couplings are usually forbidden, in order to protect these symmetries. Contrary to this approach, we show that cross couplings can play a key role and give raise to necessary corrections to flavour-mixing patterns, including a non-zero value for the reactor angle and CP violation. For definiteness, we present two models based on $A_4$. In the first model, all flavons are assumed to be real or pseudo-real, with 7 real degrees of freedom in the flavon sector in total. A sizable reactor angle associated with nearly maximal CP violation is achieved, and, as both originate from the same cross coupling, a sum rule results with a precise prediction for the value of the Dirac CP-violating phase. In the second model, the flavons are taken to be complex scalars, which can be connected with supersymmetric models and multi-Higgs models. The complexity properties of flavons provide new sources for generating the reactor angle. Models in this new approach introduce very few degrees of freedom beyond the Standard Model and can be more economical than those in the framework of extra dimension or supersymmetry.

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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.

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arXiv2015

Shifts of neutrino oscillation parameters in reactor antineutrino experiments with non-standard interactions

We discuss reactor antineutrino oscillations with non-standard interactions (NSIs) at the neutrino production and detection processes. The neutrino oscillation probability is calculated with a parametrization of the NSI parameters by splitting them into the averages and differences of the production and detection processes respectively. The average parts induce constant shifts of the neutrino mixing angles from their true values, and the difference parts can generate the energy (and baseline) dependent corrections to the initial mass-squared differences. We stress that only the shifts of mass-squared differences are measurable in reactor antineutrino experiments. Taking Jiangmen Underground Neutrino Observatory (JUNO) as an example, we analyze how NSIs influence the standard neutrino measurements and to what extent we can constrain the NSI parameters.

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arXiv2014

Predicting Lepton Flavor Mixing from $Δ(48)$ and Generalized CP Symmetries

We propose to understand the mixing angles and CP-violating phases from the $Δ(48)$ family symmetry combined with the generalized CP symmetry. A model-independent analysis is performed by scanning all the possible symmetry breaking chains. We find a new mixing pattern with only one free parameter, excellent agreement with the observed mixing angles can be achieved and all the CP-violating phases are predicted to take nontrivial values. This mixing pattern is testable in the near future neutrino oscillation and neutrinoless double-beta decay experiments. Finally, a flavor model is constructed to realize this mixing pattern.

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arXiv2014

$μ$-$τ$ reflection symmetry and radiative corrections

The $μ$-$τ$ reflection symmetry is compatible with current neutrino oscillation data and easily realized under family symmetries. We prove that this symmetry preserves $θ_{23}=45^\circ$, $δ=\pm90^\circ$, $ρ,σ=0,90^\circ$, and can be embedded into the seesaw mechanism. The $μ$-$τ$ reflection symmetry preserved at a high energy scale $Λ_\text{FS}$ will be broken by radiative corrections and result in deviations of $θ_{23}$ from $45^\circ$ and $δ$ from $\pm90^\circ$ at the electroweak scale. We develop an analytical method to derive the corrections to all the mixing parameters. We perform a numerical analysis in the MSSM for $δ=-90^\circ$ at $Λ_\text{FS}$, and observe that $θ_{23}>45^\circ$ in the normal mass ordering, $θ_{23}<45^\circ$ in the inverted mass ordering, and the sizable correction to $δ$ prefers a negative sign. These deviations have definite directions and can be tested in the future neutrino oscillation experiments.

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arXiv2014

Geometry of the effective Majorana neutrino mass in the neutrinoless double-beta decay

The neutrinoless double-beta ($0νββ$) decay is a unique process to identify the Majorana nature of massive neutrinos, and its rate depends on the size of the effective Majorana neutrino mass $\langle m\rangle_{ee}$. We put forward a novel "coupling-rod" diagram to describe $\langle m\rangle_{ee}$ in the complex plane, by which the effects of the neutrino mass ordering and CP-violating phases on $\langle m\rangle_{ee}$ are intuitively understood. We show that this geometric language allows us to easily obtain the maximum and minimum of $|\langle m\rangle_{ee}|$. It remains usable even if there is a kind of new physics contributing to $\langle m\rangle_{ee}$, and it can also be extended to describe the effective Majorana masses $\langle m\rangle_{eμ}$, $\langle m\rangle_{eτ}$, $\langle m\rangle_{μμ}$, $\langle m\rangle_{μτ}$ and $\langle m\rangle_{ττ}$ which may appear in some other lepton-number-violating processes.

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arXiv2014

Lepton Mixing Parameters from $Δ(48)$ Family Symmetry and Generalised CP

We provide a systematic and thorough exploration of the $Δ(48)$ family symmetry and the consistent generalised CP symmetry. A model-independent analysis of the achievable lepton flavor mixing is performed by considering all the possible remnant symmetries in the neutrino and the charged lepton sectors. We find a new interesting mixing pattern in which both lepton mixing angles and CP phases are nontrivial functions of a single parameter $θ$. The value of $θ$ can be fixed by the measured reactor mixing angle $θ_{13}$, and the excellent agreement with the present data can be achieved. A supersymmetric model based on $Δ(48)$ family symmetry and generalised CP symmetry is constructed, and this new mixing pattern is exactly reproduced.

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arXiv2013

Majorana phases in neutrino-antineutrino oscillations

If the massive neutrinos are Majorana particles, neutrinoless double beta ($0νββ$) decay experiments are not enough to determine the Majorana phases. We carry out a systematic study of CP violation in neutrino-antineutrino oscillations. In these processes, CP-conserving parts involve six independent $0νββ$-like mass terms $\langle m\rangle_{αβ}$ and CP-violating parts are associated with nine independent Jarlskog-like parameters ${\cal V}^{ij}_{αβ}$ (for $α, β= e, μ, τ$ and $i, j = 1, 2,3$). With the help of current neutrino oscillation data, we illustrate the salient features of six independent CP-violating asymmetries between $ν_α\to \barν_β$ and $\barν_α\to ν_β$ oscillations.

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arXiv2013

Dirac Neutrinos with $S_4$ Flavor Symmetry in Warped Extra Dimensions

We present a warped extra dimension model with the custodial symmetry $SU(2)_L\times SU(2)_R\times U(1)_X\times P_{LR}$ based on the flavor symmetry $S_4\times Z_2\times Z'_2$, and the neutrinos are taken to be Dirac particles. At leading order, the democratic lepton mixing is derived exactly, and the high dimensional operators introduce corrections of order $λ_c$ to all the three lepton mixing angles such that agreement with the experimental data can be achieved. The neutrino mass spectrum is predicted to be of the inverted hierarchy and the second octant of $θ_{23}$ is preferred. We suggest the modified democratic mixing, which is obtained by permuting the second and the third rows of the democratic mixing matrix, should be a good first order approximation to understanding sizable $θ_{13}$ and the first octant of $θ_{23}$. The constraints on the model from the electroweak precision measurements are discussed. Furthermore, we investigate the lepton mixing patterns for all the possible residual symmetries $G_ν$ and $G_{l}$ in the neutrino and charged lepton sectors, respectively.

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arXiv2013

Majorana CP-violating phases in neutrino-antineutrino oscillations and other lepton-number-violating processes

If the massive neutrinos are identified to be the Majorana particles via a convincing measurement of the neutrinoless double beta (0νββ) decay, how to determine the Majorana CP-violating phases in the 3 x 3 lepton flavor mixing matrix U will become a desirable experimental question. The answer to this question is to explore all the possible lepton-number-violating (LNV) processes in which the Majorana phases really matter. In this paper we carry out a systematic study of CP violation in neutrino-antineutrino oscillations, whose CP-conserving parts involve six independent 0νββ-like mass terms _{αβ} and CP-violating parts are associated with nine independent Jarlskog-like parameters V^{ij}_{αβ} (for α, β= e, μ, τand i, j = 1, 2,3). With the help of current neutrino oscillation data, we analyze the sensitivities of | _{αβ}| and V^{ij}_{αβ} to the three CP-violating phases of U, and illustrate the salient features of six independent CP-violating asymmetries between ν_α\to \barν_βand \barν_α\to ν_βoscillations. As a by-product, the effects of the CP-violating phases on the LNV decays of doubly- and singly-charged Higgs bosons are reexamined by taking account of the unsuppressed value of θ_{13}. Such CP-conserving LNV processes can be complementary to the possible measurements of neutrino-antineutrino oscillations in the distant future.

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arXiv2012

Neutrino masses and flavor mixing in a generalized inverse seesaw model with a universal two-zero texture

A generalized inverse seesaw model, in which the 9x9 neutrino mass matrix has vanishing (1,1) and (1,3) submatrices, is proposed. This is similar to the universal two-zero texture which gives vanishing (1,1) and (1,3) elements of the 3x3 mass matrices in both the charged lepton and neutrino sectors. We consider the Z_6 x Z_6 group to realize such texture zeros. We study this generalized inverse seesaw model systematically and derive the seesaw formula for the 3x3 mass matrix of three active neutrinos. We also analyze the universal two-zero texture in the general case and propose two ansatze to reduce the number of free parameters. Taking account of the new result of θ_{13} from the Daya Bay experiment, we constrain the parameter space of the universal two-zero texture in the general case and in the two ansatze, respectively. We find that one of the ansatze works well.

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arXiv2012

Enhanced Electromagnetic Transition Dipole Moments and Radiative Decays of Massive Neutrinos due to the Seesaw-induced Non-unitary Effects

In a simple extension of the standard electroweak theory where the phenomenon of lepton flavor mixing is described by a 3x3 unitary matrix V, the electric and magnetic dipole moments of three active neutrinos are suppressed not only by their tiny masses but also by the Glashow-Iliopoulos-Maiani (GIM) mechanism. We show that it is possible to lift the GIM suppression if the canonical seesaw mechanism of neutrino mass generation, which allows V to be slightly non-unitary, is taken into account. In view of current experimental constraints on the non-unitarity of V, we find that the effective electromagnetic transition dipole moments of three light Majorana neutrinos and the rates of their radiative decays can be maximally enhanced by a factor of O(10^2) and a factor of O(10^4), respectively. This important observation reveals an intrinsic and presumably significant correlation between the electromagnetic properties of massive neutrinos and the origin of their small masses.

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arXiv2011

The Kobayashi-Maskawa Parametrization of Lepton Flavor Mixing and Its Application to Neutrino Oscillations in Matter

We show that the Kobayashi-Maskawa (KM) parametrization of the 3 X 3 lepton flavor mixing matrix is a useful language to describe the phenomenology of neutrino oscillations. In particular, it provides us with a convenient way to link the genuine flavor mixing parameters (θ_1, θ_2, θ_3 and δ_KM) to their effective counterparts in matter (\tildeθ_1, \tildeθ_2, \tildeθ_3 and \tildeδ_KM). We rediscover the Toshev-like relation sin \tildeδ_KM sin 2\tildeθ_2 = sin δ_KM sin 2θ_2 in the KM parametrization. We make reasonable analytical approximations to the exact relations between the genuine and matter-corrected flavor mixing parameters in two different experimental scenarios: (a) the neutrino beam energy E is above O(1) GeV and (b) E is below O(1) GeV. As an example, the probability of ν_μ-> ν_e oscillations and CP-violating effects are calculated for the upcoming NOvA and Hyper-K experiments.

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arXiv2011

Non-Hermitian Perturbations to the Fritzsch Textures of Lepton and Quark Mass Matrices

We show that non-Hermitian and nearest-neighbor-interacting perturbations to the Fritzsch textures of lepton and quark mass matrices can make both of them fit current experimental data very well. In particular, we obtain θ_{23} \simeq 45^\circ for the atmospheric neutrino mixing angle and predict θ_{13} \simeq 3^\circ to 6^\circ for the smallest neutrino mixing angle when the perturbations in the lepton sector are at the 20% level. The same level of perturbations is required in the quark sector, where the Jarlskog invariant of CP violation is about 3.7 \times 10^{-5}. In comparison, the strength of leptonic CP violation is possible to reach about 1.5 \times 10^{-2} in neutrino oscillations.

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arXiv2010

A Generic Diagonalization of the 3X3 Neutrino Mass Matrix and Its Implications on the mu-tau Flavor Symmetry and Maximal CP Violation

In the flavor basis where the mass eigenstates of three charged leptons are identified with their flavor eigenstates, one may diagonalize a 3 X 3 Majorana neutrino mass matrix M_nu by means of the standard parametrization of the 3 X 3 neutrino mixing matrix V. In this treatment the unphysical phases of M_nu have to be carefully factored out, unless a special phase convention for neutrino fields is chosen so as to simplify M_nu to M'_nu without any unphysical phases. We choose this special flavor basis and establish some exact analytical relations between the matrix elements of M'_nu M'_nu^dag and seven physical parameters --- three neutrino masses (m_1, m_2, m_3), three flavor mixing angles (theta_12, theta_13, theta_23) and the Dirac CP-violating phase (delta). Such results allow us to derive the conditions for the mu-tau flavor symmetry with theta_23 = pi/4 and maximal CP violation with delta = +/- pi/2, which should be useful for discussing specific neutrino mass models. In particular, we show that theta_23 = pi/4 and delta = +/- pi/2 keep unchanged when constant matter effects are taken into account for a long-baseline neutrino oscillation experiment.

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