# Field Theories and Fluids for an Interacting Dark Sector

## TL;DR

This paper develops field theoretical models for an interacting dark sector that replicate fluid models, ensuring validity from linear to nonlinear regimes, and explores a specific Dirac-Born-Infeld coupled to quintessence example.

## Contribution

It constructs consistent field models for interacting dark sectors that match fluid descriptions at all perturbation levels, including nonlinear regimes.

## Key findings

- Field models replicate fluid interactions at linear and nonlinear levels.
- The fluid linear regime breaks before large field gradients develop.
- The specific DBI-quintessence model remains valid deep into the nonlinear regime.

## Abstract

We consider the relationship between fluid models of an interacting dark sector, and the field theoretical models that underlie such descriptions. This question is particularly important in light of suggestions that such interactions may help alleviate a number of current tensions between different cosmological datasets. We construct consistent field theory models for an interacting dark sector that behave exactly like the coupled fluid ones, even at the level of linear perturbations, and can be trusted deep in the nonlinear regime. As a specific example, we focus on the case of a Dirac, Born-Infeld (DBI) field conformally coupled to a quintessence field. We show that the fluid linear regime breaks before the field gradients become large; this means that the field theory is valid inside a large region of the fluid nonlinear regime.