arXiv subjects

Chang-Yuan Yao

Publications and source records attributed to Chang-Yuan Yao.

28 records · Page 2Linked to original sources

arXiv2021

The collider tests of a leptophilic scalar for the anomalous magnetic moments

We study the anomalous muon and electron magnetic moments by introducing a scalar with CP-violating Yukawa couplings to the lepton sector. By fitting these two magnetic moments with the recent experimental measurements, we find that such a leptophilic scalar in the mass range of $\mathcal{O}(10)- \mathcal{O}(1000 )\,\rm GeV$ can be a possible source for the current experimental deviations from the Standard Model (SM) predictions, with $\mathcal{O}(0.1) - \mathcal{O}(1)$ Yukawa couplings. The current electron and muon EDM constraints to the general CP-violating Yukawa couplings are discussed. We propose to search such a leptophilic scalar mediated at the future high-luminosity LHC (HL-LHC) runs, as well as the high-energy lepton colliders, including the CEPC and the muon collider. Our results show that the leptophilic scalar in the mass range of $\mathcal{O}(10)- \mathcal{O}(1000 )\,\rm GeV$ can be fully probed by the future experimental searches at the HL-LHC and the lepton colliders at their early stages.

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arXiv2020

Modular Invariant $A_{4}$ Models for Quarks and Leptons with Generalized CP Symmetry

We perform a systematical analysis of the $A_4$ modular models with generalized CP for the masses and flavor mixing of quarks and leptons, and the most general form of the quark and lepton mass matrices is given. The CP invariance requires all couplings real in the chosen basis and thus the vacuum expectation value of the modulus $τ$ uniquely breaks both the modular symmetry and CP symmetry. The phenomenologically viable models with minimal number of free parameters and the results of fit are presented. We find 20 models with 7 real free parameters that can accommodate the experimental data of lepton sector. We then apply $A_4$ modular symmetry to the quark sector to explain quark masses and CKM mixing matrix, the minimal viable quark model is found to contain 10 free real parameters. Finally, we give two predictive quark-lepton unification models which use only 16 real free parameters to explain the flavor patterns of both quarks and leptons.

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arXiv2020

Imprint of a new light particle at KOTO?

Recently, the KOTO experiment reported their new preliminary result of searching for the decay $K_L\toπ^0ν\barν$. Three candidate events were observed in the signal region, which exceed significantly the expectation based on the standard model. On the other hand, the new NA62 and previous BNL-E949 experiments yielded a consistent result and confirmed the standard model prediction in the charged meson decay $K^+\toπ^+ν\barν$. Furthermore, the two decays are bound by a well-motivated relation from an analysis of isospin symmetry that is hard to break by the new physics of heavy particles. In this work, we study the issue by a systematic effective field theory approach with three of the simplest scenarios, in which the $K_L$ may decay into a new light neutral particle $X$, i.e., $K_L\toπ^0X$, $K_L\to γγX$, or $K_L\toπ^0XX$. We assess the feasibility of the scenarios by simulations and by incorporating constraints coming from NA62 and other relevant experiments. Our main conclusion is that the scenario $K\toπXX$ for a long lived scalar $X$ seems more credible than the other two when combining distributions and other experimental constraints while the region below the KOTO's blind box provides a good detection environment to search for all three scenarios for a relatively heavy $X$.

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arXiv2020

Half-integral weight modular forms and application to neutrino mass models

We generalize the modular invariance approach to include the half-integral weight modular forms. Accordingly the modular group should be extended to its metaplectic covering group for consistency. We introduce the well-defined half-integral weight modular forms for congruence subgroup $Γ(4N)$ and show that they can be decomposed into the irreducible multiplets of finite metaplectic group $\widetildeΓ_{4N}$. We construct concrete expressions of the half-integral/integral modular forms for $Γ(4)$ up to weight 6 and arrange them into the irreducible representations of $\widetildeΓ_4$. We present three typical models with $\widetildeΓ_4$ modular symmetry for neutrino masses and mixing, and the phenomenological predictions of each model are analyzed numerically.

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arXiv2018

Systematic Study of One-Loop Dirac Neutrino Masses and Viable Dark Matter Candidates

We study the generation of small neutrino masses from the dimension six effective operator at tree level and one-loop level, the neutrinos are assumed to be Dirac particles. We find out all possible tree and one-loop diagrams which lead to finite neutrino masses. The relevant mediator fields and the predictions for neutrino masses are presented. The lower order contributions to neutrino masses can be forbidden by introducing soft breaking abelian symmetry or finite non-abelian symmetry. The messengers inside the loop can be dark matter particles. The possible dark matter candidates and the corresponding constraints on the parameter $α$ are analyzed for each model.

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arXiv2018

Systematic Analysis of Dirac Neutrino Masses at Dimension Five

We perform a systematic study of the Dirac neutrino masses which arise from a dimension five effective operator with a singlet scalar. We identify all possible realizations of this operator at tree level and one-loop level. The corresponding predictions for the particle content and neutrino mass matrix are presented. We add a $Z_{2}$ symmetry to forbid the renormalizable Yukawa coupling, and non-abelian discrete flavor symmetry can be used to forbid tree level diagrams in non-genuine one-loop models. The electrically neutral particle mediating the loop diagram could be dark matter candidate. We give the possible dark matter particles and the restrictions on the parameter $α$ for each model.

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arXiv2016

CP Symmetry and Lepton Mixing from a Scan of Finite Discrete Groups

Including the generalized CP symmetry, we have performed a comprehensive scan of leptonic mixing patterns which can be obtained from finite discrete groups with order less than 2000. Both the semidirect approach and its variant are considered. The lepton mixing matrices which can admit a good agreement with experimental data can be organized into eight different categories up to possible row and column permutations. These viable mixing patterns can be completely obtained from the discrete flavor groups $Δ(6n^2)$, $D^{(1)}_{9n,3n}$, $A_5$ and $Σ(168)$ combined with CP symmetry. We perform a detailed analytical and numerical analysis for each possible mixing pattern. The resulting predictions for lepton mixing parameter, neutrinoless double decay and flavored leptogenesis are studied.

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arXiv2016

Lepton Mixing Predictions from Infinite Group Series $D^{(1)}_{9n, 3n}$ with Generalized CP

We have performed a comprehensive analysis of the type D group $D^{(1)}_{9n, 3n}$ as flavor symmetry and the generalized CP symmetry. All possible residual symmetries and their consequences for the prediction of the mixing parameters are studied. We find that only one type of mixing pattern is able to accommodate the measured values of the mixing angles in both "direct" and "variant of semidirect" approaches, and four types of mixing patterns are phenomenologically viable in the "semidirect" approach. The admissible values of the mixing angles as well as CP violating phases are studied in detail for each case. It is remarkable that the first two smallest $D^{(1)}_{9n,3n}$ groups with $n=1, 2$ can fits the experimental data very well. The phenomenological predictions for neutrinoless double beta decay are discussed.

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arXiv2015

Lepton and Quark Mixing Patterns from Finite Flavor Symmetries

We perform a systematical and analytical study of lepton mixing which can be derived from the subgroups of $SU(3)$ under the assumption that neutrinos are Dirac particles. We find that type D groups can predict lepton mixing patterns compatible with the experimental data at $3σ$ level. The lepton mixing matrix turns out to be of the trimaximal form, and the Dirac CP violating phase is trivial. Moreover, we extend the flavor symmetry to the quark sector. The Cabibbo mixing between the first two generations of quarks can be generated by type D groups. Since all the finite subgroups of $U(3)$ which are not the subgroups of $SU(3)$ have not been classified, an exhaustive scan over all finite discrete groups up to order 2000 is performed with the help of the computer algebra system \texttt{GAP}. We find that only 90 (10) groups for Dirac (Majorana) neutrinos can generate the lepton mixing angles in the experimentally preferred ranges. The lepton mixing matrix is still the trimaximal pattern and the Dirac CP phase remains trivial. The smallest groups which lead to viable mixing angles are $[162, 10]$, $[162, 12]$ and $[162, 14]$. For quark flavor mixing, the correct order of magnitude of the CKM matrix elements can not be generated. Only the Cabibbo mixing is allowed even if we impose very loose constraints $0.1\leq|\left(V_{CKM}\right)_{12}|\leq0.3$ and $|\left(V_{CKM}\right)_{13}|\leq|\left(V_{CKM}\right)_{23}|<|\left(V_{CKM}\right)_{12}|$. The group $Δ(6\cdot7^2)$ can predict a Cabibbo angle $θ_q=π/14$ in good agreement with the best fit value. The groups which can give rise to both phenomenologically viable lepton mixing angles and acceptable Cabibbo angle are discussed, and the groups $Δ(6\cdot9^2)$, $[648, 259]$, $[648, 260]$, $[648, 266]$ and $Δ(6\cdot14^2)$ are especially promising.

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arXiv2015

Neutrino Mixing from CP Symmetry

The neutrino mass matrix has remnant CP symmetry expressed in terms of the lepton mixing matrix, and vice versa the remnant CP transformations allow us to reconstruct the mixing matrix. We study the scenario that all the four remnant CP transformations are preserved by the neutrino mass matrix. The most general parameterization of remnant CP transformations is presented. The lepton mixing matrix is completely fixed by the remnant CP, and its explicit form is derived. The necessary and sufficient condition for conserved Dirac CP violating phase is found. If the Klein four flavor symmetry generated by the postulated remnant CP transformations arises from a finite flavor symmetry group, the phenomenologically viable lepton flavor mixing would be the trimaximal pattern, both Dirac CP phase $δ_{CP}$ and Majorana phase $α_{31}$ are either $0$ or $π$ while another Majorana phase $α_{21}$ is a rational multiple of $π$. These general results are confirmed to be true in the case that the finite flavor symmetry group is $Δ(6n^2)$.

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