Evolution of decaying particles and decay products in various scenarios for the future expansion of the universe

TL;DR

This paper investigates how decaying particles and their relativistic decay products evolve in various future universe models, revealing different asymptotic behaviors of their energy density ratios.

Contribution

It introduces the analysis of decay processes in big rip, little rip, and pseudo-rip cosmologies, contrasting with standard $ ext{Lambda}$CDM predictions.

Findings

In big rip and little rip models, the ratio of decay products' energy density to initial particles' energy density approaches zero.

In pseudo-rip models, this ratio tends to infinity or stabilizes at a constant value.

The evolution of this ratio differs significantly across the models, affecting future universe dynamics.

Abstract

We examine nonrelativistic particles that decay into relativistic products in big rip, little rip, and pseudo-rip models for the future evolution of the universe. In contrast to decays that occur in standard $\Lambda$CDM, the evolution of the ratio $r$ of the energy density of the relativistic decay products to the energy density of the initially decaying particles can decrease with time in all of these models. In big rip and little rip models, $r$ always goes to zero asymptotically, while this ratio evolves to infinity or a constant in pseudo-rip models.