How the Scalar Field of Unified Dark Matter Models Can Cluster

TL;DR

This paper develops scalar-field models for unified dark matter and dark energy that can cluster effectively, avoiding issues like large ISW effects, and can be adapted to various dark energy behaviors.

Contribution

It introduces a reconstruction technique for scalar-field models with low sound speed, enabling clustering and flexible dark energy properties.

Findings

Models avoid large ISW effects

Scalar field can cluster effectively

Flexible to mimic various dark energy behaviors

Abstract

We use scalar-field Lagrangians with a non-canonical kinetic term to obtain unified dark matter models where both the dark matter and the dark energy, the latter mimicking a cosmological constant, are described by the scalar field itself. In this framework, we propose a technique to reconstruct models where the effective speed of sound is small enough that the scalar field can cluster. These models avoid the strong time evolution of the gravitational potential and the large Integrated Sachs-Wolfe effect which have been a serious drawback of previously considered models. Moreover, these unified dark matter scalar field models can be easily generalized to behave as dark matter plus a dark energy component behaving like any type of quintessence fluid.