Viscous Cold Dark Matter in agreement with observations

TL;DR

This paper proposes a viscous cold dark matter model that slightly suppresses structure growth, aligning with observations and potentially addressing small-scale issues of the standard bcdm model.

Contribution

It introduces a viscous cold dark matter model with small bulk viscosity, compatible with observations and offering a new approach to small-scale structure problems.

Findings

Viscous CDM slightly suppresses structure growth compared to standard CDM.

The viscous model aligns with current cosmological observations.

Potential to address small-scale clustering issues in bcdm.

Abstract

We discuss bulk viscous cosmological models. Since the bulk viscous pressure is negative, viable viscous cosmological scenarios with late time accelerated expansion can in principle be constructed. After discussing some alternative models based on bulk viscous effects we will focus on a model very similar to the standard $\Lambda$CDM. We argue that a $\Lambda${\rm v}CDM model, where we assign a very small (albeit perceptible) bulk viscosity to dark matter is in agreement with available cosmological observations. Hence, we work with the concept of viscous Cold Dark Matter ({\rm v}CDM). At the level of the perturbations, the growth of {\rm v}CDM structures is slightly suppressed when compared with the standard CDM ones. Having in mind that the small scale problems of the $\Lambda$CDM model are related to an excess of clustering, our proposal seems to indicate a possible direction for solving the serious drawbacks of the CDM paradigm within the standard cosmological model.