|M.Sc Student||Itzhak Baum|
|Subject||Top Quark Rare Decays in a Two Higgs Doublet Model|
for the Top
|Department||Department of Physics||Supervisors||Professor Emeritus Eilam Gad|
|Dr. Bar Shalom Shaouly|
|Full Thesis text|
The two Higgs doublet model for the top (T2HDM) is a model with two scalar doublets in which the top quark receives a special status. The special status of the top is manifest in the Yukawa potential, by coupling it to the second Higgs doublet, while all other quarks couple to the first Higgs doublet. The working assumption of the model is that the vacuum expectation value (VEV) of the second Higgs v2 is much larger than the first Higgs VEV v1, so that the top receives a much larger mass than all other quarks in a natural manner, and tan≡v2/v1 is large. In addition, these Yukawa couplings generate potentially enhanced flavor-changing (FC) interactions, both in the charged and the neutral sectors. These interactions can greatly enhance FC decays such as t→ch and h→tc.
In this work we explicitly (and independently) derive the Yukawa and Higgs potential of the T2HDM, obtaining the scalar to quarks and triple scalar interactions Feynman rules. We calculate the branching ratio (BR) of the one-loop and tree-level rare FC decays t→ch and h→tc in the T2HDM. We explore the BR within the parameter space of the T2HDM, focusing on regions in which BR(t→ch) and BR(h→tc) in the T2HDM can be enhanced compared to these BR's in the standard model (SM) and two Higgs doublet models (2HDM) of types I and II. We find that the BR of the rare decays t→ch and h→tc can be enhanced by many orders of magnitude in the T2HDM compared to the BR in the SM and in the 2HDM-I,II, especially in regions of the parameter space where the decays are dominated by dynamics of the neutral scalar sector.
The BR(t→ch) can be measured in the upcoming Large Hadron Collider (LHC), if its value is above ~5x10-5 which is the discovery threshold of the LHC. We find that the BR(t→ch) can exceed the LHC threshold in certain regions of the parameter space of the T2HDM, reaching up to ~10-4. Moreover, we find that the BR(h→tc) in the T2HDM can exceed ~10-4. Discovering these processes at the LHC will show a clear indication of new physics beyond the standard model, and will particularly motivate the special dynamics of the T2HDM setup.