b anti-b Higgs production at the LHC: Yukawa corrections and the leading Landau singularity

TL;DR

This paper investigates the impact of electroweak one-loop effects, especially the leading Landau singularity, on Higgs production with bottom quarks at the LHC, revealing significant deviations from tree-level predictions for higher Higgs masses.

Contribution

It provides a detailed analysis of the leading Landau singularity in Higgs production, extending the calculation of one-loop functions to include imaginary masses and assessing their effects on cross sections.

Findings

Landau singularity significantly affects cross sections at high Higgs masses.

Regulating the singularity with particle widths alters the predicted distributions.

One-loop electroweak effects can dominate over tree-level contributions for certain Higgs masses.

Abstract

At tree-level Higgs production in association with a b-quark pair proceeds through the small Yukawa bottom coupling in the Standard Model. Even in the limit where this coupling vanishes, electroweak one-loop effects, through the top-Higgs Yukawa coupling in particular, can still trigger this reaction. This contribution is small for Higgs masses around 120GeV but it quickly picks up for higher Higgs masses especially because the one-loop amplitude develops a leading Landau singularity and new thresholds open up. These effects can be viewed as the production of a pair of top quarks which rescatter to give rise to Higgs production through WW fusion. We study the leading Landau singularity in detail. Since this singularity is not integrable when the one-loop amplitude is squared, we regulate the cross section by taking into account the width of the internal top and W particles. This requires that we extend the usual box one-loop function to the case of imaginary masses. We show how this can be implemented analytically in our case. We study in some detail the cross section at the LHC as a function of the Higgs mass and show how some distributions can be drastically affected compared to the tree-level result.