Isocurvature Perturbations of Dark Energy and Dark Matter from the Swampland Conjecture

TL;DR

This paper explores how the Swampland conjecture can induce isocurvature perturbations in dark energy and dark matter, proposing a vector field as a viable dark matter candidate that avoids these issues.

Contribution

It demonstrates that the Swampland conjecture can lead to isocurvature perturbations and identifies a vector field as an effective dark matter candidate compatible with these constraints.

Findings

Isocurvature perturbations can be suppressed with a tracker solution.

A vector field of mass around 1 meV is a promising dark matter candidate.

Quantum fluctuations during high-scale inflation produce the correct dark matter abundance.

Abstract

We point out that the recently proposed Swampland conjecture on the potential gradient can lead to isocurvature perturbations of dark energy, if the quintessence field acquires large quantum fluctuations during high-scale inflation preferred by the conjecture. Also, if the quintessence field is coupled to a dark sector that contains dark matter, isocurvature perturbation of dark matter is similarly induced. Both isocurvature perturbations can be suppressed if the quintessence potential allows a tracker solution in the early Universe. We find that a vector field of mass $\lesssim {\cal O}(1)$ meV is an excellent dark matter candidate in this context, not only because the right abundance is known to be produced by quantum fluctuations during high-scale inflation without running afoul of isocurvature bounds, but also because its coupling to the quintessence does not spoil the flatness of the potential.