Phenomenology of Unified Dark Matter models with fast transition

TL;DR

This paper investigates a simple Unified Dark Matter model with a rapid transition from matter-like behavior to a dark energy-like epoch, analyzing its background evolution and perturbations to assess its observational distinguishability from standard cosmology.

Contribution

It introduces and analyzes a simple UDM model with a fast transition, exploring its background dynamics and perturbation properties to evaluate its viability.

Findings

The model exhibits a rapid transition consistent with observed acceleration.

Perturbation analysis shows potential observational signatures differentiating it from ΛCDM.

The viability of the model depends on specific features of the transition and perturbation behavior.

Abstract

A fast transition between a standard matter-like era and a late $\Lambda$CDM-like epoch generated by a single Unified Dark Matter component can explain the observed acceleration of the Universe. UDM models with a fast transition should be clearly distinguishable from $\Lambda$CDM (and alternatives) through observations. Here we focus on a particularly simple model and analyse its viability by studying features of the background model and properties of the adiabatic UDM perturbations.