CP violation and circular polarisation in neutrino radiative decay

TL;DR

This paper explores how $CP$ violation in neutrino radiative decay can generate circular polarisation asymmetries, providing a new avenue for understanding particle physics phenomena and potential dark matter signals.

Contribution

It establishes a general formalism linking $CP$ violation to circular polarisation in neutrino decays for both Dirac and Majorana fermions, applicable to various models.

Findings

Derived the connection between $CP$ violation and circular polarisation.

Applied the formalism to neutrino decay scenarios relevant to dark matter and leptogenesis.

Discussed phenomenological implications for astrophysical observations.

Abstract

The radiative decay of neutral fermions has been studied for decades but $CP$ violation induced within such a paradigm has evaded attention. $CP$ violation in these processes can produce an asymmetry between circularly polarised directions of the radiated photons and produces an important source of net circular polarisation in particle and astroparticle physics observables. The results presented in this work outlines the general connection between $CP$ violation and circular polarisation for both Dirac and Majorana fermions and can be used for any class of models that produce such radiative decays. The total $CP$ violation is calculated based on a widely studied Yukawa interaction considered in both active and sterile neutrino radiative decay scenarios as well as searches for dark matter via direct detection and collider signatures. Finally, the phenomenological implications of the formalism on keV sterile neutrino decay, leptogenesis-induced right-handed neutrino radiative decay and IceCube-driven heavy dark matter decay are discussed.