# Higgs interference effects at the one-loop level in the 1-Higgs-Singlet extension of the Standard Model

## TL;DR

This paper investigates one-loop Higgs interference effects in the 1-Higgs-Singlet extension of the Standard Model, emphasizing their impact on WW and tt decay channels with heavy Higgs masses, and provides a publicly available computational implementation.

## Contribution

It presents a detailed calculation of Higgs interference effects at one-loop level in the 1HSM, including the impact of absorptive parts and challenging the common K-factor approximation, with a publicly available implementation.

## Key findings

- Interference effects significantly affect Higgs signal distributions.
- The K-factor approximation is inadequate for interference calculations.
- The implementation is available in Sherpa+OpenLoops for further research.

## Abstract

A detailed study of Higgs interference effects at the one-loop level in the 1-Higgs-Singlet extension of the Standard Model (1HSM) is presented for the WW and tt decay modes with fully leptonic WW decay. We explore interference effects for benchmark points with a heavy Higgs mass that significantly exceeds 2*m_t. In the WW channel, the Higgs signal and the interfering continuum background are loop induced. In the tt channel, which features a tree-level background, we also calculate the interference with the one-loop background, which, due to the appearance of the absorptive part, is found to dominate the normalisation and shape of differential Higgs distributions and should therefore be considered in experimental analyses. The commonly used geometric average K-factor approximation K_interference ~ (K_Higgs*K_background)^(1/2) is not appropriate. We calculate with massive top and bottom quarks. Our 1HSM and SM implementation in Sherpa+OpenLoops is publicly available and can be used as parton-level integrator or event generator.