Two-loop helicity amplitudes for diphoton production with massive quark loop

TL;DR

This paper presents the calculation of two-loop helicity amplitudes in QCD for diphoton production involving a massive quark loop, essential for precise predictions at the LHC.

Contribution

It introduces a full mass-dependent computation of two-loop amplitudes for diphoton production, enabling higher-order QCD corrections with massive quark effects.

Findings

Finite remainders obtained after renormalization.

Helicity decomposition achieved using physical projectors.

Framework for future cross-section calculations with massive quarks.

Abstract

We compute two-loop helicity amplitudes in QCD for diphoton production through quark- and gluon-initiated channels, accounting for a massive internal quark loop by keeping its full mass dependence. Using physical projectors, we directly decompose the amplitude into its helicity components. By renormalising the heavy quark mass in on-shell, and other quantities in $\overline{\rm MS}$ schemes, we obtain finite remainders. This work paves the way for calculating the cross-section for diphoton production at higher orders in QCD with a massive quark loop, employing different subtraction schemes. The effect of a heavy quark is expected to play a crucial role in high-luminosity LHC.