Unphysical properties in a class of interacting dark energy models

TL;DR

This paper investigates interacting dark energy models with a specific parameterization, revealing that negative interaction parameters lead to violations of fundamental energy conditions and cause unphysical instabilities, questioning their physical viability.

Contribution

The study demonstrates that certain parameter choices in interacting dark energy models result in unphysical properties, highlighting limitations of these models.

Findings

Negative interaction parameter $\xi$ violates the Weak Energy Condition.

Models with $\xi<0$ exhibit instabilities in matter perturbations.

Current observational support for negative $\xi$ conflicts with physical consistency.

Abstract

Models with non-gravitational interactions between the dark matter and dark energy components are an alternative to the standard cosmological scenario. These models are characterized by an interaction term, and a frequently used parameterization is $Q = 3\xi H \rho_{x}$, where $H$ is the Hubble parameter and $\rho_{x}$ is the dark energy density. Although current observations support such a model for negative values of the interaction parameter $\xi$, we show here that this interval of values of $\xi$ leads the model to predict a violation of the Weak Energy Condition (WEC) for the dark matter density, regardless of the value of the equation-of-state parameter of the dark energy component. This violation is accompanied by unphysical instabilities of matter perturbations.