Cosmology with a Non-minimally Coupled Dark Matter Fluid I. Background Evolution

TL;DR

This paper investigates a cosmological model where dark matter non-minimally couples to gravity, leading to modified early universe dynamics that could resolve the horizon, flatness, and singularity problems without extra fields.

Contribution

It introduces a novel non-minimal coupling of dark matter to gravity that alters early universe evolution, providing potential solutions to fundamental cosmological issues.

Findings

Modified Friedmann equations with non-minimal coupling.

A phase of accelerated expansion driven by dark matter coupling.

Possibility of a cosmological bounce replacing the initial singularity.

Abstract

We explore a cosmological model in which dark matter is non-minimally coupled to gravity at the fluid level. While typically subdominant compared to Standard Model forces, such couplings may dominate dark matter dynamics. We show that this interaction modifies the early-time Friedmann equations, driving a phase of accelerated expansion that can resolve the horizon and flatness problems without introducing additional fields. At even earlier times, the coupling to spatial curvature may give rise to a cosmological bounce, replacing the initial singularity of standard cosmology. These results suggest that non-minimally coupled dark matter could offer a unified framework for addressing both the singularity and fine-tuning problems.