Cosmological perturbations in a generalised axion-like dark energy model

TL;DR

This paper investigates the evolution and perturbations of a generalized axion-like dark energy model, exploring its potential to explain late-time cosmic acceleration and its observational signatures.

Contribution

It introduces a multi-fluid approach to analyze cosmological perturbations in a generalized axion-like dark energy model, including non-adiabatic effects and initial conditions.

Findings

Model exhibits tracking behavior reducing the coincidence problem

Perturbation analysis includes gravitational potential and matter power spectrum

Certain parameter ranges are favored by observational data

Abstract

We analyse the cosmological evolution of a generalised axion-like field that drives the late-time acceleration of the Universe. This model can exhibit tracking behaviour, which alleviates the coincidence problem. The cosmological perturbations are carried within a multi-fluid approach where the scalar field is described by a non-adiabatic fluid, i.e., one whose speed of sound in the rest frame differs from the adiabatic one. The cosmological perturbations are solved since the radiation-dominated epoch, imposing initial adiabatic conditions for matter, radiation and the dark energy component, for modes well outside the Hubble horizon in the past. We analyse the homogeneous curvature perturbation, gravitational potential and dark energy perturbations in this model, as well as the matter power spectrum and f{\sigma}8. We discuss which parameters of the model are more favoured observationally.