Anomalous Couplings from the Electroweak Chiral Lagrangian for Off-Shell Higgs in $gg\to Z_L Z_L$

TL;DR

This paper explores how off-shell Higgs production in gluon fusion can reveal anomalous couplings, using the electroweak chiral Lagrangian to systematically analyze EFT contributions at high energies.

Contribution

It provides a systematic EFT framework for analyzing off-shell Higgs effects in $gg o Z_L Z_L$, identifying key parameters and their phenomenological implications.

Findings

Two parameters describe leading-order new physics effects.

Subleading EFT effects are expected to be small.

Power counting enables systematic EFT application.

Abstract

We investigate the production of (longitudinal) $Z$-boson pairs in gluon fusion as a probe of anomalous Higgs couplings. Of particular interest is the kinematic region of large center-of-mass energy, where the Higgs-boson is highly off-shell. We employ the electroweak chiral Lagrangian with a light Higgs, which is the most natural effective field theory (EFT) for this process. We demonstrate this by a detailed analysis of the leading and next-to-leading EFT contributions to the amplitude, at leading order in QCD, emphasizing the role of power counting for a systematic application of the EFT. We show that at leading order the new-physics contributions are described by only two parameters, which depend on three EFT couplings. Subleading effects can be expected to be small within the range of validity of the EFT. Phenomenological implications are briefly discussed.