Observational Properties of Feebly Coupled Dark Matter

TL;DR

This paper investigates how feebly coupled hidden sectors, specifically a Higgs portal scalar dark matter model, can have observable effects and derives bounds on the scalar self-coupling based on cosmological and astrophysical constraints.

Contribution

It provides the first detailed analysis of observational constraints on feebly coupled hidden sector dark matter models, focusing on the Higgs portal scenario.

Findings

Bounds on scalar self-coupling: $10^{-4} \,\lesssim\, \lambda_s \lesssim 0.2$ for specific parameters.

Non-observation of isocurvature perturbations constrains dark matter models.

Astrophysical limits on self-interactions further restrict model parameters.

Abstract

We show that decoupled hidden sectors can have observational consequences. As a representative model example, we study dark matter production in the Higgs portal model with one real singlet scalar $s$ coupled to the Standard Model Higgs via $\lambda_{\rm hs}\Phi^\dagger\Phi s^2$ and demonstrate how the combination of non-observation of cosmological isocurvature perturbations and astrophysical limits on dark matter self-interactions imply stringent bounds on the magnitude of the scalar self-coupling $\lambda_{\rm s}s^4$. For example, for dark matter mass $m_{\rm s}=10$ MeV and Hubble scale during cosmic inflation $H_*=10^{12}$ GeV, we find $10^{-4}\lesssim \lambda_{\rm s}\lesssim 0.2$.