We examine nonrelativistic particles that decay into relativistic products in big rip, little rip, and pseudorip models for the future evolution of the Universe. In contrast to decays that occur in standard $\mathrm{\Lambda }\mathrm{CDM}$, 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 pseudorip models.

• Received 23 July 2021
• Accepted 19 November 2021

DOI:https://doi.org/10.1103/PhysRevD.104.123506