CDM and Baryons as Distinct Fluids in a Linear Approximation for the Growth of Structure

TL;DR

This paper shows that treating baryons and dark matter as separate fluids in linear structure growth models can significantly impact predictions, affecting tests of cosmological models and interpretations of observational data.

Contribution

It introduces a refined linear approximation that accounts for distinct baryon and dark matter perturbations, improving the accuracy of structure formation predictions.

Findings

Separate baryon and dark matter growth affects structure formation predictions.

Impacts the comparison between $\\Lambda$CDM and modified gravity models.

Potentially influences 21cm tomography constraints.

Abstract

A single fluid approximation which treats perturbations in baryons and dark matter as equal has sometimes been used to calculate the growth of linear matter density perturbations in the Universe. We demonstrate that properly accounting for the separate growth of baryon and dark matter fluctuations can change some predictions of structure formation in the linear domain in a way that can alter conclusions about the consistency between predictions and observations for $\Lambda$CDM models versus modified gravity scenarios . Our results may also be useful for 21cm tomography constraints on alternative cosmological models for the formation of large scale structure.