Metastable Dark Energy with Radioactive-like Decay

TL;DR

This paper introduces a novel metastable dark energy model with a decay rate akin to radioactive decay, affecting the universe's expansion and fitting observational data better than standard models.

Contribution

It proposes a new class of dark energy decay models with a constant decay rate independent of external parameters, inspired by radioactive decay, and tests their compatibility with cosmological data.

Findings

Decay half-life must be much larger than the universe's age.

Models with dark energy decaying into dark matter fit high-redshift BAO data better.

Dark energy decay influences the universe's expansion history.

Abstract

We propose a new class of metastable dark energy (DE) phenomenological models in which the DE decay rate does not depend on external parameters such as the scale factor or the curvature of the Universe. Instead, the DE decay rate is assumed to be a constant depending only on intrinsic properties of DE and the type of a decay channel, similar to case of the radioactive decay of unstable particles and nuclei. As a consequence, the DE energy density becomes a function of the proper time elapsed since its formation, presumably in the very early Universe. Such a natural type of DE decay can profoundly affect the expansion history of the Universe and its age. Metastable DE can decay in three distinct ways: (i) exponentially, (ii) into dark matter, (iii) into dark radiation. Testing metastable DE models with observational data we find that the decay half-life must be many times larger than the age of the Universe. Models in which dark energy decays into dark matter lead to lower values of the Hubble parameter at large redshifts relative to $\Lambda$CDM. Consequently these models provide a better fit to cosmological BAO data (especially data from from high redshift quasars) than concordance ($\Lambda$CDM) cosmology.