Precision Electroweak Data and Unification of Couplings in Warped Extra Dimensions

TL;DR

This work analyzes gauge coupling unification in warped extra dimensions with bulk gauge fields and fermions, localized the Higgs on the IR brane, and introduces brane-localized gauge kinetic terms to reconcile TeV-scale KK modes with precision electroweak data. It develops a 4D effective theory that captures oblique and non-oblique corrections via $G_f$, $G_{ff}$, and $\tilde{G}_0(L,L)$, and computes their dependence on fermion localization parameters and brane terms. The authors show that, with modest IR brane kinetic terms and appropriate fermion profiles, the model yields KK masses in the few-TeV range while remaining consistent with EW constraints, particularly when a heavier Higgs partially cancels oblique contributions. The study highlights a viable, testable alternative to SUSY GUTs, with potential LHC signatures from KK gauge bosons and the GUT sector, and emphasizes the predictive role of logarithmic running in the warped framework for gauge coupling unification.

Abstract

Warped extra dimensions allow a novel way of solving the hierarchy problem, with all fundamental mass parameters of the theory naturally of the order of the Planck scale. The observable value of the Higgs vacuum expectation value is red-shifted, due to the localization of the Higgs field in the extra dimension. It has been recently observed that, when the gauge fields propagate in the bulk, unification of the gauge couplings may be achieved. Moreover, the propagation of fermions in the bulk allows for a simple solution to potentially dangerous proton decay problems. However, bulk gauge fields and fermions pose a phenomenological challenge, since they tend to induce large corrections to the precision electroweak observables. In this article, we study in detail the effect of gauge and fermion fields propagating in the bulk in the presence of gauge brane kinetic terms compatible with gauge coupling unification, and we present ways of obtaining a consistent description of experimental data, while allowing values of the first Kaluza Klein mode masses of the order of a few TeV.

Figures (4)

• Figure 1: Behavior of $G_f/G_f^\infty$ (left) and $G_{ff}/G_{ff}^\infty$ (right) as a function of $c_f$, where the superscript $\infty$ indicates $c_f = +\infty$ (fermions localized on the UV brane). The curves correspond to $k\,r_{UV} = 0$ (red), $k\,r_{UV} = 10$ (blue) and $k\,r_{UV} = -10$ (green). In all of them we took $k\,r_{IR} = 0$ and $kL = 30$.
• Figure 2: Behavior of $G_f/\tilde{G}_0(L, L)$ (left) and $G_{ff}/\tilde{G}_0(L, L)$ (right) as a function of $c_f$. The curves correspond to $k\,r_{UV} = 0$ (red), $k\,r_{UV} = 10$ (blue) and $k\,r_{UV} = -10$ (green). In all of them we took $k\,r_{IR} = 0$ and $kL = 30$.
• Figure 3: Allowed bands of the RS unified model in the parameter space of the Higgs mass and the first KK mode mass. The central green band represents $1\sigma$ agreement with the electroweak fit to $S$ and $T$ (with $U=0$), whereas the surrounding blue and red bands indicate $2\sigma$ and $3\sigma$ agreement, respectively.
• Figure 4: As Fig. \ref{['fig:massesc']}, but with non-zero (unified) kinetic terms on the IR brane of $k r_{IR} = 1,2$.