Particle decays and stability on the de Sitter universe

TL;DR

This paper investigates particle decay processes in de Sitter space-time, revealing that particles above a critical mass are unstable and decay occurs even when forbidden in flat space, with decay characteristics depending on mass.

Contribution

It provides an exact calculation of the phase space coefficient and analyzes particle stability and decay behavior specific to de Sitter space.

Findings

Particles above critical mass are unstable and decay occurs.

Decay lifetime is independent of velocity for large particles.

Particles below critical mass have quantized decay products and zero lifetime.

Abstract

We study particle decay in de Sitter space-time as given by first order perturbation theory in a Lagrangian interacting quantum field theory. We study in detail the adiabatic limit of the perturbative amplitude and compute the "phase space" coefficient exactly in the case of two equal particles produced in the disintegration. We show that for fields with masses above a critical mass $m_c$ there is no such thing as particle stability, so that decays forbidden in flat space-time do occur here. The lifetime of such a particle also turns out to be independent of its velocity when that lifetime is comparable with de Sitter radius. Particles with mass lower than critical have a completely different behavior: the masses of their decay products must obey quantification rules, and their lifetime is zero.