Variable sound speed in interacting dark energy models

TL;DR

This paper introduces a new class of interacting dark energy models with variable sound speed, analyzing their effects on cosmological observations and comparing them to the standard Lambda Cold Dark Matter model.

Contribution

It presents a self-consistent framework for models with variable dark energy sound speed and explores their observational implications and parameter constraints.

Findings

Dark energy sound speed can deviate from unity in momentum exchange interactions.

Interaction affects the cosmic microwave background and matter power spectrum.

Models show distinct signatures compared to Lambda CDM in cosmological data.

Abstract

We consider a self-consistent and physical approach to interacting dark energy models described by a Lagrangian, and identify a new class of models with variable dark energy sound speed. We show that if the interaction between dark energy in the form of quintessence and cold dark matter is purely momentum exchange this generally leads to a dark energy sound speed that deviates from unity. Choosing a specific sub-case, we study its phenomenology by investigating the effects of the interaction on the cosmic microwave background and linear matter power spectrum. We also perform a global fitting of cosmological parameters using CMB data, and compare our findings to $\Lambda$CDM.