Precision Higgs Constraints in U(1) Extensions of the Standard Model with a Light Z'-Boson

TL;DR

This paper investigates how measurements of Higgs decays into light Z' bosons in U(1) extended models can impose tighter constraints on new physics parameters than traditional Higgs signal strength analyses.

Contribution

It provides detailed calculations of scalar production and decay in models with light Z' bosons, linking Higgs decay channels to new gauge sector constraints.

Findings

Higgs decay to Z' Z' can have a significant branching ratio.

Higgs signal strength measurements can set stronger bounds on model parameters.

Intertwined searches for scalar s and Z' bosons improve detection prospects.

Abstract

Anomaly free $U(1)$ extensions of the standard model (SM) predict a new neutral gauge boson $Z'$. When the $Z'$ obtains its mass from the spontaneous breaking of the new $U(1)$ symmetry by a new complex scalar field, the model also predicts a second real scalar $s$ and the searches for the new scalar and the new gauge boson become intertwined. We present the computation of production cross sections and decay widths of such a scalar $s$ in models with a light $Z'$ boson, when the decay $h\to Z' Z'$ may have a sizeable branching ratio. We show how Higgs signal strength measurement in this channel can provide stricter exclusion bounds on the parameters of the model than those obtained from the total signal strength for Higgs boson production.