Angular momentum non-conserving decays in isotropic media

TL;DR

This paper demonstrates that certain particle decays forbidden in vacuum due to angular momentum conservation can occur in isotropic media, highlighting medium-induced effects on decay processes.

Contribution

It provides explicit examples of angular momentum non-conserving decays in isotropic media, expanding understanding of medium effects on particle decay mechanisms.

Findings

Decay of a scalar into a photon and another scalar in medium is possible.

Neutrino decay into another neutrino and a graviton can occur in isotropic media.

Medium effects enable forbidden decay channels in particle physics.

Abstract

Various processes that are forbidden in the vacuum due to angular momentum conservation can occur in a medium that is isotropic and does not carry any angular momentum. We illustrate this by considering explicitly two examples. The first one is the decay of a spin-0 particle into a photon and another spin-0 particle, using a model involving the Yukawa interactions of the scalar particles with a charged fermion field. The second one involves the decay of a neutrino into another neutrino and a graviton, in the standard model of particle interactions augmented with the linearized gravitational couplings.