PHENOMENOLOGY OF WARPED EXTRA DIMENSIONS

Abstract

Warped extra dimensions provide a very interesting and attractive framework that solves the hierarchy problem of the Standard Model (SM) of particle physics through the curvature along an extra dimension. In this thesis I will discuss various aspects of collider phenomenology of warped extra dimensions. First, I will discuss a class of models within this framework that are very attractive due to their naturalness, which are called warped/composite Pseudo-Goldstone Boson (PGB) Higgs models. A generic prediction of these models is the existence of extra gauge bosons (called coset gauge bosons), which give rise to distinctive signatures at the Large Hadron Collider (LHC). However, due to the large masses (beyond 3 Teraelectronvolt (TeV)) of the coset gauge bosons and their small couplings to standard model states, their discovery would be very challenging at the LHC, and an upgrade of the LHC is needed. My second topic is about the phenomenology of the Higgs boson in warped extra dimensions. In models where fermions propagate in the extra dimension, there exist heavy excitations of SM fermions, which are called the Kaluza-Klein (KK) fermions. These KK states give sizable new contributions to the production and decay channels of the Higgs boson. I will give a detailed analysis of the Higgs boson couplings to massless vector bosons (gluons and photons) in warped extra dimensions. I will show that KK fermions of all generations contribute to these couplings, leading to significant deviation from the prediction of the SM. Therefore, precision measurement of the properties of the Higgs boson can shed light on the structure of warped extra dimensions even if KK particles cannot be directly produced at the LHC due to their heavy masses.