Off-shell Higgs Interpretations Task Force: Models and Effective Field Theories Subgroup Report

TL;DR

This report reviews how off-shell Higgs measurements can enhance searches for BSM physics within EFT frameworks, discussing theoretical models, computational tools, and potential for new constraints beyond existing global fits.

Contribution

It advances understanding of off-shell Higgs effects in EFT, reviews computational methods, and explores prospects for new BSM constraints using off-shell measurements.

Findings

Off-shell measurements can resolve flat directions in parameter space.

Sensitivity of off-shell processes to SMEFT dimension-6 operators is demonstrated.

Potential to improve BSM constraints beyond current global fits.

Abstract

This report presents the results of the Models and Effective Field Theories Subgroup of the Off-Shell Interpretations Task Force in the LHC Higgs Working Group. The main goal of the subgroup was to discuss and advance the potential impact of off-shell Higgs measurements on searches for BSM physics carried out in the EFT framework or as benchmark model studies. In the first contribution, the off-shell potential to resolve flat directions in parameter space for on-shell measurements is studied. Furthermore, the sensitivity of off-shell measurements to SMEFT dimension-6 operators for the gg $\to$ ZZ process is discussed, and studies of explicit models that are testable in off-shell production are reviewed. In the second contribution, the SMEFT effects in the off-shell gluon fusion and electroweak processes are discussed. Subsequently, the computation of integrated and differential effects using SMEFT@NLO and MG5_aMC@NLO, or JHUGen and MCFM, is demonstrated. On that basis, a study of the prospects of obtaining additional SMEFT constraints - beyond those from existing global fits - by utilising the off-shell process is presented. For clarification, a revised introduction, definition and discussion of the Higgs basis parametrisation of the SMEFT is given in the third contribution. In short notes on the SMEFT, the Higgs basis with an additional constraint is discussed and relations between the Higgs and Warsaw bases are presented. Lastly, an overview of EFT calculations and tools is given.