Gluon Fusion Processes at One-loop within the Standard Model and Beyond

TL;DR

This thesis analyzes gluon fusion processes at one-loop level within the Standard Model and beyond, focusing on electroweak boson production and extra-dimensional models, with implications for LHC physics and new physics searches.

Contribution

It provides the first detailed calculations of gluon fusion processes involving electroweak bosons and KK-gravitons, including their contributions at higher orders in QCD.

Findings

Gluon fusion processes can produce electroweak boson pairs with significant cross sections.

Extra-dimensional models predict KK-graviton production via gluon fusion at the LHC.

These processes serve as important backgrounds and tests for the Standard Model and new physics.

Abstract

In this thesis, we have studied certain gluon fusion processes which proceed via quark loop diagrams at the leading order. The fact that these gluon-gluon channel processes are independent processes, their contributions towards the total/differential hadronic cross sections can be calculated separately. We have considered the production of a pair of electroweak vector bosons in association with a jet via gluon fusion within the standard model. These processes were not accessible at earlier hadron colliders such as the Tevatron. Therefore, observation of these rare processes at the LHC will be a test of the standard model itself. Like the di-vector boson production via gluon fusion processes, these processes are also important backgrounds for many new physics signals, and the standard model Higgs boson signal at the LHC. These leading order gluon fusion processes contribute to the corresponding hadronic processes at the next-to-next-to-leading order in {\alpha}_s. We have taken a model of extra-dimensions, the ADD (Arkani-Hamed, Dimopoulos and Dvali) model, as the possible candidate of new physics at the LHC. This model tries to solve the hierarchy problem of the standard model by proposing large extra space dimensions which may be accessible at TeV scale. We have considered the direct production of KK-gravitons (GKK) in association with an electroweak boson (H/{\gamma}/Z) via gluon fusion. These processes contribute to the corresponding hadronic processes at the next-to-leading order in {\alpha}_s. Many interesting issues related to the fermion loop amplitudes have also been discussed.