Complex Mass Scheme and Higgs Phenomenology

Abstract

This thesis will deal with the phenomenological aspects of calculations involving unstable particles. In the first part we discuss techniques used in the treatment of unstable particles such as the complex mass scheme and the narrow width approximation. We show the complex mass scheme allows us to include finite width effects while providing gauge invariant results, both for a fermionic and a bosonic resonance. In the second part we move towards Higgs phenomenology computations. We present a full calculation of the Higgs production cross section $\sigma (gg\rightarrow H)$ through top quark loop as well as for the Higgs decay width $\Gamma (H\rightarrow \gamma\gamma)$, which includes fermion and W boson loops. Respectively, these processes correspond to the dominant Higgs production mechanism at hadron colliders and to the decay mode used for the discovery of the Higgs boson at the LHC. Lastly, we write a Monte Carlo C++ event generator which provides the cross section for Higgs production associated with top quark pair $\sigma (qq\rightarrow t\overline{t}H)$, and which can be readily modified to output any of the usual desired quantities and plots, as well as unweighted events.