Phenomenological implications on a hidden sector from the Festina Lente bound

TL;DR

This paper explores how the Festina Lente bound constrains hidden sector particles with $U(1)$ gauge symmetries, notably ruling out ultra-light milli-charged particles and impacting fuzzy bosonic dark matter models.

Contribution

It applies the Festina Lente bound to hidden sectors, deriving new constraints on milli-charged particles and dark matter models with hidden gauge symmetries.

Findings

Milli-charged particles with mass below 5 meV are forbidden by the FL bound.

The FL bound constrains fuzzy bosonic dark matter models with very small masses.

The bound applies independently of kinetic mixing strength.

Abstract

We apply the Festina Lente (FL) bound on a hidden sector with $U(1)$ gauge symmetries. Since the FL bound puts a lower bound on masses of particles charged under the $U(1)$ gauge symmetries, it is possible to constrain the hidden sector even with a tiny coupling to the Standard Model. In particular, we focus on the phenomenological implications of the FL bound on milli-charged particles, which naturally arise when kinetic mixing between the photon and the hidden photon is allowed. It turns out that the milli-charged particle with the mass $M\lesssim 5$ meV is prohibited by the FL bound in the case of a single hidden $U(1)$, independent of the value of kinetic mixing. This bound is crucial when bosonic dark matter is taken in consideration in this framework: the fuzzy bosonic dark matter models requesting minuscule masses are ruled out by the FL bound if the longevity of dark matter is protected by the hidden gauge symmetry.