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Brane-localized Kinetic Terms in the Randall-Sundrum Model

H. Davoudiasl, J. L. Hewett, T. G. Rizzo

TL;DR

The paper addresses the RS framework with bulk SM gauge fields by introducing brane-localized kinetic terms (BLKT's) on the Planck and TeV branes, deriving the modified gauge KK wavefunctions, masses, and especially the mode-dependent couplings to TeV-brane fermions. It shows that for natural BLKT parameters the gauge-fermion couplings can be suppressed relative to the original RS predictions, weakening precision electroweak constraints on the lightest KK mass $m_1$ and allowing $ ext{m}_1$ to lie in the few-hundred-GeV range, which corresponds to $ ext{Λ}_ ext{π}$ potentially near $10$ TeV. This relaxation makes the RS scenario with bulk gauge fields more compatible with a low electroweak scale and suggests near-degeneracy between gauge KK states and gravitons in large regions of parameter space, with distinctive collider implications. The work highlights that BLKT's are generic in orbifold constructions and can substantially modify RS phenomenology, motivating further exploration for other bulk fields (e.g., gravitons).

Abstract

We examine the effects of boundary kinetic terms in the Randall-Sundrum model with gauge fields in the bulk. We derive the resulting gauge Kaluza-Klein (KK) state wavefunctions and their corresponding masses, as well as the KK gauge field couplings to boundary fermions, and find that they are modified in the presence of the boundary terms. In particular, for natural choices of the parameters, these fermionic couplings can be substantially suppressed compared to those in the conventional Randall-Sundrum scenario. This results in a significant relaxation of the bound on the lightest gauge KK mass obtained from precision electroweak data; we demonstrate that this bound can be as low as a few hundred GeV. Due to the relationship between the lightest gauge KK state and the electroweak scale in this model, this weakened constraint allows for the electroweak scale to be near a TeV in this minimal extension of the Randall-Sundrum model with bulk gauge fields, as opposed to the conventional scenario.

Brane-localized Kinetic Terms in the Randall-Sundrum Model

TL;DR

The paper addresses the RS framework with bulk SM gauge fields by introducing brane-localized kinetic terms (BLKT's) on the Planck and TeV branes, deriving the modified gauge KK wavefunctions, masses, and especially the mode-dependent couplings to TeV-brane fermions. It shows that for natural BLKT parameters the gauge-fermion couplings can be suppressed relative to the original RS predictions, weakening precision electroweak constraints on the lightest KK mass and allowing to lie in the few-hundred-GeV range, which corresponds to potentially near TeV. This relaxation makes the RS scenario with bulk gauge fields more compatible with a low electroweak scale and suggests near-degeneracy between gauge KK states and gravitons in large regions of parameter space, with distinctive collider implications. The work highlights that BLKT's are generic in orbifold constructions and can substantially modify RS phenomenology, motivating further exploration for other bulk fields (e.g., gravitons).

Abstract

We examine the effects of boundary kinetic terms in the Randall-Sundrum model with gauge fields in the bulk. We derive the resulting gauge Kaluza-Klein (KK) state wavefunctions and their corresponding masses, as well as the KK gauge field couplings to boundary fermions, and find that they are modified in the presence of the boundary terms. In particular, for natural choices of the parameters, these fermionic couplings can be substantially suppressed compared to those in the conventional Randall-Sundrum scenario. This results in a significant relaxation of the bound on the lightest gauge KK mass obtained from precision electroweak data; we demonstrate that this bound can be as low as a few hundred GeV. Due to the relationship between the lightest gauge KK state and the electroweak scale in this model, this weakened constraint allows for the electroweak scale to be near a TeV in this minimal extension of the Randall-Sundrum model with bulk gauge fields, as opposed to the conventional scenario.

Paper Structure

This paper contains 2 sections, 16 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Formalism

Figures (1)

  • Figure 1: (a) The behavior of the first five roots as $\delta_\pi$ is varied, assuming $\delta_0=0$. Note the sharp increase in $x_n$ near $\delta_\pi=0$ for all KK levels. (b) The large negative $\delta_\pi$ region is expanded to show the new root originating at the value $\delta_\pi= -kr_c\pi\simeq -35.4$.