Characterizing LHC-Resonances in extended HEFT: information on the nature of extended scalar sectors

TL;DR

This paper develops a gauge-invariant effective field theory framework to analyze and interpret potential new scalar resonances at colliders, providing structural relations between observables to distinguish their underlying nature.

Contribution

It introduces an extended HEFT approach that systematically relates collider observables to the UV properties of new scalars, aiding model interpretation without detailed model testing.

Findings

Hierarchies between Wilson coefficients are systematically evaluated.

Structural relations between collider observables are derived.

Application to the 95 GeV resonance illustrates the framework's utility.

Abstract

In theories with extended scalar sectors the lightest new scalar degree of freedom might be accessible at colliders. Going beyond simplified models, such a theory can be described in a gauge-invariant and agnostic way via an EFT with a non-linearly realized electroweak symmetry. In this extended HEFT, depending on the $SU(2)$ nature of the new scalar in the UV, operators will be suppressed by different powers of a heavy mass scale. We use dimensional analysis to systematically evaluate expected hierarchies between Wilson coefficients, leading to structural relations between potential LHC observables, such as di-boson resonances, tau pair production or the di-photon channel. Once future collider data reveals a hint of a new scalar field, it can be fitted to this extended HEFT and such a structural analysis will help interpret it with respect to possible UV models, circumventing the need to individually test each possible model on the data or to fix the $SU(2)$ representation of the new scalar beforehand. For illustration, the framework is applied to the tentative 95 GeV resonance. In addition to its usefulness for collider physics, the extended HEFT can also be beneficial for low-energy observables, allowing to describe new scalars in an agnostic way.