Observational constraints on soft dark energy and soft dark matter: challenging $\Lambda$CDM

TL;DR

This paper investigates soft cosmology models with scale-dependent dark sector equations of state using observational data, finding that these models are favored over the standard $\\Lambda$CDM cosmology.

Contribution

It introduces and constrains soft dark energy and dark matter models with scale-dependent equations of state using multiple cosmological datasets.

Findings

Softness parameters deviate from $\\Lambda$CDM values in data.

Models with soft dark energy are strongly favored over $\\Lambda$CDM.

Soft cosmology models are supported by Bayesian evidence analysis.

Abstract

Soft cosmology is an extension of standard cosmology allowing for a scale-dependent equation-of-state (EoS) parameter in the dark sectors, which is one of the properties of soft materials in condensed-matter physics, that may arise either intrinsically or effectively. We use data from Cosmic Microwave Background (CMB), Baryonic Acoustic Oscillations (BAO), Supernovae Type Ia (SNIa), and Redshift space distrotion (RSD) probes, in order to impose observational constraints on soft dark energy and soft dark matter. We examine three simple models, corresponding to the minimum extensions of $\Lambda$CDM scenario, namely we consider that at large scales the dark sectors have the EoS's of $\Lambda$CDM model (dust dark matter and cosmological constant respectively), while at intermediate scales either dark energy or dark matter or both, may have a different EoS according to constant "softness" parameters $s_{de}$ and $s_{dm}$. The observational confrontation shows that for almost all datasets the softness parameters deviate from their $\Lambda$CDM values, in a prominent way for soft dark energy and mildly for soft dark matter, and thus the data favor soft cosmology. Finally, performing a Bayesian evidence analysis we find that the examined models are certainly preferred over $\Lambda$CDM cosmology.