Bounds on the Fermion-Bulk Masses in Models with Universal Extra Dimensions

TL;DR

This paper investigates how bulk fermion masses in models with universal extra dimensions affect experimental observables, setting bounds on these masses through precision measurements, dark matter, and collider data, with LHC expected to further constrain the parameters.

Contribution

It provides the first comprehensive bounds on bulk fermion masses in universal extra dimension models using current experimental data.

Findings

Current bounds on universal bulk mass are smaller than (0.2-0.3)/R.

Non-universal bulk masses have slightly relaxed bounds.

LHC will further constrain the parameter space.

Abstract

In models with extra dimensions, vectorlike Dirac masses for fermion fields are generically allowed. These masses are independent of electroweak symmetry breaking and do not contribute to the known masses for the quarks and leptons. They control the profile of the bulk wave functions, the mass spectra of Kaluza-Klein modes, and interactions that could be tested in experiments. In this article, we study the effects of bulk masses in electroweak precision measurements and in dark matter and collider searches, to set bounds on the bulk mass parameters in models with a flat universal extra dimension, namely, Split-UED. We find the current bound on the universal bulk-mass to be smaller than (0.2-0.3)/R, where R is the radius of the extra dimension. Similar but slightly relaxed bounds are obtained in the non-universal bulk mass case. The LHC is expected to play an important role in constraining the remaining parameter space.