Virtual QCD corrections to $gg \to ZZ$: top-quark loops from a transverse-momentum expansion

TL;DR

This paper computes the virtual QCD corrections to gluon-gluon to Z-boson pair production involving top-quark loops, using a transverse-momentum expansion to produce a comprehensive analytic result across all phase space.

Contribution

It introduces a novel method combining small-transverse-momentum and high-energy expansions to evaluate two-loop top-quark loop corrections in gg to ZZ processes.

Findings

Provides an analytic expression valid in the entire phase space.

Enables improved modeling of Higgs signal-background interference.

Facilitates more accurate background estimations in off-shell Higgs analyses.

Abstract

We present the virtual corrections due to the top-quark loops for the process $gg \to ZZ$ at next-to-leading order in QCD. The associated two-loop box diagrams are computed using a small-transverse-momentum expansion. Our results are then merged with those available in the complementary energy region, obtained via a high-energy expansion, in order to provide an analytic result that is valid in the whole phase space. The results presented allow for an efficient modelling of the signal--background interference as well as the irreducible background in off-shell Higgs production.