On the impact of non-factorisable corrections in VBF single and double Higgs production

TL;DR

This paper analyzes the effects of non-factorisable QCD corrections on VBF single and double Higgs production, showing their relative size and impact under different conditions, and implementing the results in updated computational tools.

Contribution

It provides a detailed calculation of non-factorisable corrections at NNLO for VBF Higgs production, including their comparison to factorisable corrections and validation of the eikonal approximation.

Findings

Non-factorisable corrections are within scale uncertainties after cuts for single Higgs.

Without cuts, non-factorisable corrections slightly exceed scale uncertainties.

Double Higgs production shows larger non-factorisable corrections due to diagram cancellations.

Abstract

We study the factorisable and non-factorisable QCD corrections to Vector-Boson Fusion single and double Higgs production and show the combined corrections for both processes at $\mathcal{O}(\alpha_s^2)$. We investigate the validity of the eikonal approximation with and without selection cuts, and carry out an in-depth study of the relative size of the non-factorisable next-to-next-to-leading order corrections compared to the factorisable ones. In the case of single Higgs production, after selection cuts are applied, the non-factorisable corrections are found to be mostly contained within the factorisable scale uncertainty bands. When no cuts are applied, instead, the non-factorisable corrections are slightly outside the scale uncertainty band. Interestingly, for double Higgs production, we find that both before and after applying cuts, non-factorisable corrections are enhanced compared to the single Higgs case. We trace this enhancement to the existence of delicate cancellations between the various leading-order Feynman diagrams, which are partly spoiled by radiative corrections. All the studied contributions have been implemented in proVBFH v1.2.0 and proVBFHH v1.1.0.