|Ph.D Student||Geller Michael|
|Subject||Higgs Physics, Electroweak Symmetry Breaking and Extended|
Quark Sector at the LHC
|Department||Department of Physics||Supervisors||Professor Emeritus Gad Eilam|
|Dr. Shaouly Bar Shalom|
|Full Thesis text|
The standard model of particle physics describes all the known particles and interactions, with the exception of gravity. Despite its experimental success, the SM has a few crucial flaws and shortcomings. The foremost of these is the "naturalness problem" of the Higgs - the colossal amount of tuning required to keep the SM valid far in the UV.
The extensions of the SM addressing these issue have been thoroughly studied in the literature. Most of the extensions have in common the existence of new "top partner" states responsible for cancelling the top loops. The top partners are required to be light to avoid fine-tuning, and they are typically easy to produce and discover at colliders.
No such state has been discovered yet and thus it is interesting to consider alternatives to these scenarios. Such an alternative is the "neutral naturalness" approach, wherein the top partners are neutral under the SM gauge group and thus avoid discovery at the LHC. The main part of this thesis focuses on the best known example of "neutral naturalness" - the twin Higgs model. In this work, we UV-complete the twin Higgs in the composite Higgs framework where the Higgs is a composite pseudo-Goldstone boson in the coset of SO(8)/SO(7). Unlike ordinary composite Higgs where the top loops are cancelled due to composite top partners, naturalness is now restored due to new "mirror states" living in the copy of the SM. These states have no SM charges and will not appear in any LHC searches. The composite states, on the contrary, are charged under the SM gauge group and can be discovered in collider searches. These, however, no longer play the role of top partners and can naturally appear above the LHC reach. We study the flavor constraints on this model and find that that they can be satisfied without any additional flavor structure at the expense of O(1%) tuning in the Higgs potential.
Beyond the naturalness problem, there are experimental motivations for studying BSM phenomenology as well. In particular, all sensible alternatives for the SM should be tested experimentally. The second part of this thesis concentrates on a few of these alternatives, on their compatibility with the current experimental data and on the possible predictions for future experiments. In this part we focus on two distinct BSM scenarios - the SM extended with a fourth generation of quarks and leptons and a possible extra-dimensional interpretation of the 125 GeV state.