Signs of a non-zero equation-of-state for Dark Matter

Abstract

We demonstrate how a changing and negative equation-of-state (EoS) for dark matter can alleviate cosmic tensions and explain the integrated Sachs-Wolfe (ISW) void anomaly. We discuss the effect of the model on the cosmic expansion history, growth of structure and the ISW. We show that a negative EoS at late times is able to produce a larger Hubble constant and smaller ${\sigma }_8$, which can explain both cosmological tensions. Furthermore, the model uniquely predicts larger ISW at low redshift, a prediction which is in agreement with observations of larger ISW from voids. The preference for a negative EoS for dark matter at late times is indicative of a unified dark sector and degenerate with models of dark matter and dark energy interaction. Future measurements of the ISW from cosmic voids can provide a unique test for this solution to tensions in cosmology, should they continue to persist.

arXiv commentInvited chapter for the edited book Hubble Constant Tension (Eds. E. Di Valentino and D. Brout, Springer Singapore, expected in 2024)