DESI-Like Hubble Expansion From Staged Symmetry Breaking

TL;DR

This paper proposes a natural effective field theory model where a subcomponent of dark matter has a time-varying equation of state, potentially resolving tensions in cosmological data and producing self-interacting dark matter with velocity-dependent interactions.

Contribution

It introduces a novel effective field theory framework for dark matter with a dynamic equation of state and self-interactions, addressing observational tensions.

Findings

Dark matter with a time-varying equation of state is achievable in a natural EFT.

The model predicts self-interacting dark matter with velocity-dependent cross sections.

Potential to reconcile small-scale structure observations with cosmological data.

Abstract

The Dark Energy Spectroscopic Instrument (DESI) second data release shows a moderate preference for dark energy with a time-varying equation of state parameter, suggesting that the standard $\Lambda$CDM model may need to be revised. In particular, DESI favors dark energy whose equation of state parameter can drop below $-1$, violating the null energy condition. Chen and Loeb have recently suggested that this violation may be avoided if a subcomponent of the dark matter possesses a time-dependent equation of state. In this work, we present a realization of that idea which can be regarded as a more natural effective field theory. We show that such a construction not only yields dark matter with a time-varying equation of state parameter, but also naturally produces a self-interacting dark matter candidate with a velocity-dependent cross section as a consequence of gauge invariance. The second feature is relevant for addressing tensions between $\Lambda$CDM and observations of small-scale structure, particularly the diversity of galactic rotation curves.