The singlet scalar as FIMP dark matter

TL;DR

This paper explores the singlet scalar model as a FIMP dark matter candidate, showing it can produce the correct relic density with extremely small couplings, leading to no detectable signals in current experiments.

Contribution

It identifies a new viable parameter region for singlet scalar dark matter in the FIMP regime, expanding the model's phenomenological possibilities.

Findings

New parameter space with couplings 10^-11 to 10^-12 for GeV-TeV masses.

Dark matter relic density can be achieved without thermal equilibrium.

No expected signals at direct or indirect detection experiments.

Abstract

The singlet scalar model is a minimal extension of the Standard Model that can explain the dark matter. We point out that in this model the dark matter constraint can be satisfied not only in the already considered WIMP regime but also, for much smaller couplings, in the Feebly Interacting Massive Particle (FIMP) regime. In it, dark matter particles are slowly produced in the early Universe but are never abundant enough to reach thermal equilibrium or annihilate among themselves. This alternative framework is as simple and predictive as the WIMP scenario but it gives rise to a completely different dark matter phenomenology. After reviewing the calculation of the dark matter relic density in the FIMP regime, we study in detail the evolution of the dark matter abundance in the early Universe and the predicted relic density as a function of the parameters of the model. A new dark matter compatible region of the singlet model is identified, featuring couplings of order 10^-11 to 10^-12 for singlet masses in the GeV to TeV range. As a consequence, no signals at direct or indirect detection experiments are expected. The relevance of this new viable region for the correct interpretation of recent experimental bounds is emphasized.