Understanding the suppression of structure formation from dark matter$\unicode{x2013}$dark energy momentum coupling

TL;DR

This paper investigates how scalar field dark energy coupled via momentum to dark matter suppresses structure formation, providing analytical and numerical insights, and generalizing to power law couplings with varying potential slopes.

Contribution

It analytically and numerically demonstrates that momentum coupling between dark energy and dark matter suppresses structure growth, extending previous quadratic models to more general power law couplings.

Findings

Suppression of structure growth is a generic feature of power law couplings.

The suppression can be larger than previously found for certain parameters.

Analytical and numerical methods confirm the physical mechanism behind the suppression.

Abstract

Models in which scalar field dark energy interacts with dark matter via a pure momentum coupling have previously been found to potentially ease the structure formation tension between early- and late-universe observations. In this article we explore the physical mechanism underlying this feature. We argue analytically that the perturbation growth equations imply the suppression of structure growth, illustrating our discussion with numerical calculations. Then we generalise the previously studied quadratic coupling between the dark energy and dark matter to a more general power law case, also allowing for the slope of the dark energy exponential potential to vary. We find that the structure growth suppression is a generic feature of power law couplings and it can, for a range of parameter values, be larger than previously found.