Cosmological Constraints on an Invisibly Decaying Higgs Boson

TL;DR

The paper addresses small-scale structure problems in CDM by introducing a light, self-interacting scalar DM candidate (phion) that couples to the Higgs through the portal coupling $g'$. Using thermal history, relic abundance calculations, and Higgs-mediated annihilation physics, it derives cosmological bounds on the parameters $g'$, $m_\phi$, and $m_h$. It finds that a phion with $m_\phi \sim 0.1$ GeV is excluded, while for $m_\phi \sim 1$ GeV achieving $\Omega_\phi h^2 \approx 0.3$ requires $g' \gtrsim 2$ and $m_h \lesssim 130$ GeV, which implies the invisible decay $h\to \phi\phi$ dominates. As a consequence, the model yields collider-testable signatures via Higgs invisible decays and demonstrates how Higgs-sector parameters constrain self-interacting DM scenarios, while noting challenges with alternative DM annihilation scenarios and the origin of $m_\phi$.

Abstract

Working in the context of a proposal for collisional dark matter, we derive bounds on the Higgs boson coupling $g^{\prime}$ to a stable light scalar particle, which we refer to as phion ($φ$), required to solve problems with small scale structure formation which arise in collisionless dark matter models. We discuss the behaviour of the phion in the early universe for different ranges of its mass. We find that a phion in the mass range of 100 MeV is excluded and that a phion in the mass range of 1 GeV requires a large coupling constant, $g^{\prime} \gsim 2$, and $m_h \lsim 130$ GeV in order to avoid overabundance, in which case the invisible decay mode of the Higgs boson would be dominant.

Figures (2)

• Figure 1: Feynman diagramm for phion annihilation via Higgs exchange.
• Figure 2: Contour of $\Omega_\phi h^2=0.3$ as a function of $m_h$ (in GeV) and $g^\prime$, for $m_{\phi}=0.5~\hbox{GeV}$ (top), $1.0,~1.5$ and $2~\hbox{GeV}$ (bottom).