# Dark Energy, the Swampland and the Equivalence Principle

## TL;DR

This paper explores how string theory constraints on de Sitter vacua influence models of dark energy involving scalar fields coupled to dark matter, with implications for the equivalence principle and cosmological observations.

## Contribution

It proposes scenarios with finite-field minima for scalar couplings, analyzing their consistency with observations and potential to reconcile swampland conjectures with dark energy models.

## Key findings

- Coupling functions with finite minima can grow over time and fit cosmological data.
- Such couplings may alleviate tensions between swampland criteria and dark energy potentials.
- Violations of the equivalence principle could be observable in the non-linear regime.

## Abstract

It has recently been argued that string theory does not admit de Sitter vacua. This would imply that the current accelerated expansion of the universe is not driven by a cosmological constant (or vacuum energy) but by other means such as a quintessential scalar field. Such a scalar field is in general expected to couple to at least some matter species, such as dark matter. Cosmological observations already constrain such dark matter couplings strongly. We argue that there are a number of interesting scenarios to be explored, such as coupling functions which possess a minimum at finite field values. In these theories, the effective gravitational coupling between dark matter particles grows with time and are consistent with observations of the anisotropies in the cosmic microwave background radiation and large scale structures. We argue that such couplings might also help to alleviate the tension between the swampland conjectures and the properties of the quintessential potential. Observational signatures of violations of the equivalence principle in the dark sector are expected in the non-linear regime on intermediate or small scales.