On the robustness of the indirect determination of the width of the detected Higgs boson

TL;DR

This paper examines the robustness of the indirect Higgs width measurement at the LHC, showing that in many extended models, the bounds remain valid, with only moderate weakening under certain conditions.

Contribution

It analyzes how different Standard Model extensions affect the indirect Higgs width bounds, demonstrating their robustness across a wide parameter space.

Findings

Indirect bounds are valid in large parameter regions.

Small-mass new particles can weaken the bounds.

Experimental searches can further constrain models.

Abstract

The indirect determination of the total width of the detected Higgs boson that is carried out by the experimental collaborations at the LHC relies on the assumption that the coupling modifiers for the on-shell and off-shell couplings are the same. However, physics beyond the Standard Model affecting the on-shell and off-shell regions differently could invalidate this assumption, so that the actual width of the detected Higgs boson could be larger than the bounds obtained under this assumption. Relaxing the assumption and investigating different types of extensions of the Standard Model, we analyse under which conditions a larger total width of the detected Higgs boson is compatible with all experimental and theoretical constraints. For the considered scenarios of scalar extensions with an additional state contributing as a resonance or at the loop level, we find that the indirect bounds obtained by ATLAS and CMS remain valid over large parts of the parameter space, with the exception of parameter regions where the additional particles have relatively small masses. We discuss the potential of experimental searches for new particles to further constrain such scenarios. Based on the existing experimental and theoretical constraints we conclude that relaxing the assumption of equal on-shell and off-shell coupling modifiers that is used in the experimental analyses at the LHC yields an upper bound on the total width of the detected Higgs boson in realistic extensions of the Standard Model that is only weakened by up to a factor of about two compared to the case where this assumption is valid.