Top Yukawa Deviation in Extra Dimension

TL;DR

This paper proposes a five-dimensional Higgs model where the top Yukawa coupling can deviate from the standard model, potentially observable at the LHC, and explores two scenarios with different fermion localizations.

Contribution

It introduces a simple extra-dimensional model with brane-localized Higgs potentials that predicts measurable top Yukawa deviations and discusses their experimental implications.

Findings

Top Yukawa coupling can be smaller than standard model expectation.

Sizable top Yukawa deviation is possible and detectable at the LHC.

Both scenarios are consistent with electroweak precision tests.

Abstract

We suggest a simple one-Higgs-doublet model living in the bulk of five-dimensional spacetime compactified on $S^1/Z_2$, in which the top Yukawa coupling can be smaller than the naive standard-model expectation, i.e. the top quark mass divided by the Higgs vacuum expectation value. If we find only single Higgs particle at the LHC and also observe the top Yukawa deviation, our scenario becomes a realistic candidate beyond the standard model. The Yukawa deviation comes from the fact that the wave function profile of the free physical Higgs field can become different from that of the vacuum expectation value, due to the presence of the brane-localized Higgs potentials. In the Brane-Localized Fermion scenario, we find sizable top Yukawa deviation, which could be checked at the LHC experiment, with a dominant Higgs production channel being the $WW$ fusion. We also study the Bulk Fermion scenario with brane-localized Higgs potential, which resembles the Universal Extra Dimension model with a stable dark matter candidate. We show that both scenarios are consistent with the current electroweak precision measurements.