Influence of strongly coupled, hidden scalars on Higgs signals

TL;DR

The paper analyzes how a light hidden sector coupled to the Standard Model Higgs via an $O(N)$-symmetric scalar extension (Phions) can dramatically broaden the Higgs resonance, effectively making the Higgs width $\Gamma_H$ a free parameter. Using a large-$N$ expansion, the Higgs propagator acquires a self-energy $\Sigma(s,\mu^2)$ from Phion bubbles, broadening the resonance and diluting signals when couplings are strong. The authors derive one-loop RG bounds to constrain the model up to high scales and perform detailed collider phenomenology for LEP1/LEP2, NLC, and LHC, showing that large hidden-sector couplings can render a light Higgs undetectable at these facilities. They conclude that missing-energy channels provide strong constraints on hidden-sector couplings, while LHC visibility of invisible decays is limited, highlighting hidden sectors as a plausible explanation for non-observation of a SM-like Higgs.

Abstract

To investigate the possible effects of a light hidden sector on Higgs boson detection, we discuss a model of scalar singlets coupled to the Standard Model. The model effectively makes the Higgs width a free parameter due to additional invisible decay modes. This width can become arbitrarily large. Theoretical and experimental bounds on model parameters are presented. It is shown, how Standard Model predictions change and that in the case of large coupling, Higgs signals will be diluted. We study, to which extent such a strongly coupled, hidden sector can be excluded by present and future Higgs search experiments.

Figures (8)

• Figure 1: The ratio $\gamma_H/m_H$ for several values of $\kappa$ and $m_H=50, 100$ GeV. Lower lines for given $M_H$ belong to lower values of $\kappa$.
• Figure 2: Higgs width in comparison with the Standard Model.
• Figure 3: Theoretical limits on the parameters of the model in the $\omega$ vs. $M_H$ plane. The contour lines correspond to the cutoff scales $\Lambda = 10^{19}$, $10^6$, $10^4$ and $10^3$ GeV.
• Figure 4: Relevant Feynman graphs for invisible Higgs search at LEP2.
• Figure 5: Example of a missing energy differential cross section at LEP2 with $M_H=105$ GeV, $\sqrt{s}=205$ GeV for several values of $\omega$.