ISW effect in Unified Dark Matter Scalar Field Cosmologies: an analytical approach

TL;DR

This paper analytically investigates the ISW effect in Unified Dark Matter models based on scalar fields, emphasizing the impact of sound speed on CMB anisotropies and potential deviations from standard cosmology.

Contribution

It provides a general analytical framework for the ISW effect in unified dark matter models, highlighting the role of sound speed across different formulations.

Findings

Sound speed critically influences ISW effect deviations.

Analytical expressions applicable to various unified dark matter models.

Potential observable differences from ΛCDM in CMB anisotropies.

Abstract

We perform an analytical study of the Integrated Sachs-Wolfe (ISW) effect within the framework of Unified Dark Matter models based on a scalar field which aim at a unified description of dark energy and dark matter. Computing the temperature power spectrum of the Cosmic Microwave Background anisotropies we are able to isolate those contributions that can potentially lead to strong deviations from the usual ISW effect occurring in a $\Lambda$CDM universe. This helps to highlight the crucial role played by the sound speed in the Unified Dark Matter models. Our treatment is completely general in that all the results depend only on the speed of sound of the dark component and thus it can be applied to a variety of unified models, including those which are not described by a scalar field but relies on a single dark fluid.