M.Sc Thesis

M.Sc StudentSurujon Ze'ev
SubjectPhenomenology of Models with Extra Dimensions
DepartmentDepartment of Physics
Supervisors PROF. Yael Shadmi
MR Yuval Grossman


    The puzzle of flavor hierarchy in the standard model may be explained by separating the fermions in extra dimensions.   The resulting four dimensional observables are suppressed by exponentially small overlaps of separated fermion wave-functions.   In order to localize fermions in the extra dimensions, one or more gauge singlet scalars are introduced.   In such “split fermion” models, several assumptions have commonly been made.   One of these assumptions is that the Higgs vacuum expectation value (VEV) is either uniform throughout the extra space, or confined to a “brane”.   The theoretical motivation for these choices is not clear.   In particular, the Higgs VEV cannot be uniform since it couples to the localizing scalars.   We study the assumptions that are needed in order to generate such configurations, and provide an underlying mechanism for generating them.   Another assumption that has always been made in the split fermion models is that the fermion fields couple diagonally to the localizing scalars.   In that case flavor mixing occur only due to the couplings of the fermions to the standard model Higgs field. We relax this simplifying assumption and allow order one non diagonal couplings to the localizer.   We find that within this scenario of “twisted split fermions”, the hierarchical flavor structure of the Standard Model can be recovered in the effective four dimensional theory.   Moreover, in this case the standard model flavor structure can arise from the fermion coupling to the localizing scalars even when the five dimensional Yukawa couplings to the Higgs are universal.