One-Loop Yukawa Corrections to the Process pp -> b anti-b H in the Standard Model at the LHC: Landau Singularities

TL;DR

This paper calculates electroweak one-loop corrections, including Landau singularities, to Higgs production with bottom quarks at the LHC, revealing significant effects at higher Higgs masses.

Contribution

It provides a detailed analysis of Landau singularities in one-loop diagrams and extends the calculation to include complex masses for internal particles.

Findings

Electroweak corrections become significant for Higgs masses above 120 GeV.

Landau singularities affect the amplitude and require regularization with particle widths.

Distributions at the LHC can differ drastically from tree-level predictions.

Abstract

We calculate the leading electroweak (EW) corrections to the important process of Higgs production associated with two bottom quarks at the CERN Large Hadron Collider (LHC). Our study is restricted to the Standard Model (SM). 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, EW 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. An important part of the thesis is devoted to the topic of Landau singularities in one-loop Feynman diagrams and application to the specific process of bbH production at the LHC. Since the 4-point leading Landau 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 complex 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.