Unmodified Gravity

TL;DR

This paper explores how relaxing the assumption of purely gravitational dark energy-dark matter interactions affects cosmic structure growth, providing analytic solutions and highlighting potential biases in gravity tests.

Contribution

It introduces simple analytic solutions for structure growth in models with energy transfer in the dark sector, emphasizing the importance of dark sector physics in cosmological analyses.

Findings

Neglecting dark sector physics can bias growth rate measurements.

Analytic solutions reveal significant effects on structure formation.

Potential false signatures of modified gravity due to dark energy decay.

Abstract

By relaxing the conventional assumption of a purely gravitational interaction between dark energy and dark matter, substantial alterations to the growth of cosmological structure can occur. In this work we focus on the homogeneous transfer of energy from a decaying form of dark energy. We present simple analytic solutions to the modified growth rates of matter fluctuations in these models, and demonstrate that neglecting physics within the dark sector may induce a significant bias in the inferred growth rate, potentially offering a false signature of modified gravity.