# Unification of Dark Matter - Dark Energy in Generalized Galileon Theories

## TL;DR

This paper proposes a unified model within generalized Galileon theories that describes dark matter and dark energy as a single cosmic fluid, matching observations and remaining stable at perturbative levels.

## Contribution

It introduces a shift-symmetric generalized Galileon model that unifies dark matter and dark energy without a cosmological constant, fitting observational data and ensuring stability.

## Key findings

- Effective cosmic fluid with w_U=0 during matter era
- Transition to accelerated expansion at z~0.5
- Stable at scalar and tensor perturbations

## Abstract

We present a unified description of the dark matter and the dark energy sectors, in the framework of shift-symmetric generalized Galileon theories. Considering a particular combination of terms in the Horndeski Lagrangian in which we have not introduced a cosmological constant or a matter sector, we obtain an effective unified cosmic fluid whose equation of state $w_U$ is zero during the whole matter era, namely from redshifts $z\sim3000$ up to $z\sim2-3$. Then at smaller redshifts it starts decreasing, passing the bound $w_U=-1/3$, which marks the onset of acceleration, at around $z\sim0.5$. At present times it acquires the value $w_U=-0.7$. Finally, it tends toward a de-Sitter phase in the far future. This behaviour is in excellent agreement with observations. Additionally, confrontation with Supernovae type Ia data leads to a very efficient fit. Examining the model at the perturbative level, we show that it is free from pathologies such as ghosts and Laplacian instabilities, at both scalar and tensor sectors, at all times.