Precision calculations for $h \to WW/ZZ \to 4$ fermions in a Singlet Extension of the Standard Model with Prophecy4f

TL;DR

This paper extends the Standard Model with a singlet scalar, computes precise decay corrections for the Higgs to four fermions, and implements these in Prophecy4f for experimental analysis.

Contribution

It provides next-to-leading-order electroweak and QCD corrections for Higgs decays in a singlet extension, with analysis of scheme dependence and implementation in Prophecy4f.

Findings

Deviations from the Standard Model Higgs width are below 10%.

Renormalization scheme conversion effects are significant.

Reduced scale and scheme dependence at NLO.

Abstract

We consider an extension of the Standard Model by a real singlet scalar field with a $Z_2$-symmetric Lagrangian and spontaneous symmetry breaking with vacuum expectation value for the singlet. Considering the lighter of the two scalars of the theory to be the 125GeV Higgs particle, we parametrize the scalar sector by the mass of the heavy Higgs boson, a mixing angle $\alpha$, and a scalar Higgs self-coupling $\lambda_{12}$. Taking into account theoretical constraints from perturbativity and vacuum stability, we compute next-to-leading-order electroweak and QCD corrections to the decays $h\to WW/ZZ \to 4$ fermions of the light Higgs boson for some scenarios proposed in the literature. We formulate two renormalization schemes and investigate the conversion of the input parameters between the schemes, finding sizeable effects. Solving the renormalization-group equations for the MSbar parameters $\alpha$ and $\lambda_{12}$, we observe a significantly reduced scale and scheme dependence in the next-to-leading-order results. For some scenarios suggested in the literature, the total decay width for the process $h \to 4f$ is computed as a function of the mixing angle and compared to the width of a corresponding Standard Model Higgs boson, revealing deviations below 10%. Differential distributions do not show significant distortions by effects beyond the Standard Model. The calculations are implemented in the Monte Carlo generator Prophecy4f, which is ready for applications in data analyses in the framework of the singlet extension.