Ye-Ling Zhou

Baryogenesis via leptonic CP-violating phase transition

Abstract We propose a new mechanism to generate a lepton asymmetry based on the vacuum CP-violating phase transition (CPPT). This approach differs from classical thermal leptogenesis as a specific seesaw model, and its UV completion, need not be specified. The lepton asymmetry is generated via the dynamically realised coupling of the Weinberg operator during the phase transition. This mechanism provides a connection with low-energy neutrino observables.

The role of flavon cross couplings in leptonic flavour mixing

A bstractIn 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 A4. 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.

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

A bstractIn 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 A4 discrete symmetry. In A4 models, a Z3 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− → μ+e−e−, e+μ−μ−, and the other 3-body and all radiative decays are suppressed by small Z3-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 Br(τ− → μ+e−e−) ≈ Br(τ− → e+μ−μ−) and Br(τ− → e−γ) ≈ Br(τ− → μ−γ). In case ii, we observe that the mixing between two Z3-covariant flavons plays an important role. All processes are suppressed by charged lepton masses and current experimental con- straints 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.

Renormalization-group equations of neutrino masses and flavor mixing parameters in matter

A bstractWe borrow the general idea of renormalization-group equations (RGEs) to understand how neutrino masses and flavor mixing parameters evolve when neutrinos propagate in a medium, highlighting a meaningful possibility that the genuine flavor quantities in vacuum can be extrapolated from their matter-corrected counterparts to be measured in some realistic neutrino oscillation experiments. Taking the matter parameter a≡22GFNeE

On neutrino mixing in matter and CP and T violation effects in neutrino oscillations.

a\equiv 2\sqrt{2}\kern0.5em {G}_{\mathrm{F}}{N}_eE

Leptonic flavour mixing influenced by flavon cross couplings.

to be an arbitrary scale-like variable with Ne being the net electron number density and E being the neutrino beam energy, we derive a complete set of differential equations for the effective neutrino mixing matrix V and the effective neutrino masses m˜i

Leptogenesis via Varying Weinberg Operator: a Semi-Classical Approach.

{\tilde{m}}_i