Spontaneous leptonic CP violation and nonzero $\theta_{13}$

TL;DR

This paper presents a model extending the Standard Model with additional Higgs triplets and a scalar singlet, explaining spontaneous leptonic CP violation, nonzero $ heta_{13}$, and linking leptogenesis with low-energy CP phases.

Contribution

It introduces a new framework combining flavor symmetry breaking and scalar extensions to explain neutrino mixing and CP violation phenomena.

Findings

The model accommodates the measured $ heta_{13}$ value from Daya Bay.

It predicts large Dirac CP violation consistent with experimental data.

Leptogenesis viability is demonstrated through triplet decay CP asymmetries.

Abstract

We consider a simple extension of the Standard Model by adding two Higgs triplets and a complex scalar singlet to its particle content. In this framework, the CP symmetry is spontaneously broken at high energies by the complex vacuum expectation value of the scalar singlet. Such a breaking leads to leptonic CP violation at low energies. The model also exhibits an $A_4\times Z_4$ flavour symmetry which, after being spontaneously broken at a high-energy scale, yields a tribimaximal pattern in the lepton sector. We consider small perturbations around the tribimaximal vacuum alignment condition in order to generate nonzero values of $\theta_{13}$, as required by the latest neutrino oscillation data. It is shown that the value of $\theta_{13}$ recently measured by the Daya Bay Reactor Neutrino Experiment can be accommodated in our framework together with large Dirac-type CP violation. We also address the viability of leptogenesis in our model through the out-of-equilibrium decays of the Higgs triplets. In particular, the CP asymmetries in the triplet decays into two leptons are computed and it is shown that the effective leptogenesis and low-energy CP-violating phases are directly linked.