Effective field theory approach to the Higgs lineshape

TL;DR

This paper introduces an effective field theory method to accurately describe the lineshape of broad Higgs resonances, ensuring gauge invariance and unitarity, which is crucial for LHC phenomenology involving unstable particles.

Contribution

It presents a novel EFT-based formulation for the Higgs lineshape that addresses off-shell effects and broad resonance descriptions, improving upon existing approaches.

Findings

The method produces gauge-invariant amplitudes for broad resonances.

It effectively describes the Higgs lineshape in gluon fusion, vector boson scattering, and top pair production.

The approach maintains unitarity and is applicable to LHC phenomenology.

Abstract

The phenomenology of unstable particles, including searches and exclusion limits at the LHC, depends significantly on its lineshape. When the width of the resonance is large with respect to its mass, off-shell effects become relevant and the very same definition of width becomes non trivial. Taking a heavy Higgs boson as an example, we propose a new formulation to describe the lineshape via an effective field theory approach. Our method leads to amplitudes that are gauge invariant, respect unitarity and can appropriately describe the lineshape of broad resonances. The application of the method to the following relevant processes for the LHC phenomenology have been considered: gluon fusion, vector boson scattering and $t\bar{t}$ production via weak boson fusion.