Lorentz-symmetry violating decays in a medium

TL;DR

This paper demonstrates that certain decay processes forbidden in vacuum can occur in a medium, mimicking Lorentz violation effects, through a model-independent analysis of the vertex function.

Contribution

It provides a model-independent framework showing how medium-induced effects can enable forbidden decays, simulating Lorentz symmetry violation without breaking fundamental symmetries.

Findings

Forbidden decays can occur in a medium due to medium effects.

The amplitude remains consistent with symmetry principles despite non-zero results.

Medium effects can mimic Lorentz violation in decay processes.

Abstract

Various decay processes, such as the decay of a spin-1 particle into two photons or the gravitational decay of a spin-1/2 fermion, are forbidden in the vacuum by a combination of requirements, including angular momentum conservation, Lorentz invariance and gauge invariance. We show that such processes can occur in a medium, such as a thermal background of particles, even if it is homogeneous and isotropic. We carry out a model-independent analysis of the vertex function for such processes in terms of a set of form factors, and show that the amplitude can be non-zero while remaining consistent with the symmetry principles mentioned above. The results simulate Lorentz symmetry violating effects, although in this case they arise from completely Lorentz-invariant physics.