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Electroweak Constraints on Extended Models with Extra Dimensions

Christopher D. Carone

TL;DR

The paper investigates electroweak precision constraints on extensions of the Standard Model with extra dimensions, focusing on three representative bulk/brane assignments for gauge, Higgs, and chiral matter. It derives how Kaluza-Klein excitations and mass mixing modify electroweak observables and computes bounds on the compactification scale $M_c=1/R$ for δ=1, finding typical limits in the 1.5–4 TeV range while highlighting model-dependent variations. The results show that bulk leptons can yield the strongest bounds due to Z–KK mixing, SU(2)-brane scenarios are constrained mainly by G_F, and bulk generations depend strongly on the bulk vs brane Higgs vev ratio; these constraints imply that KK states are generally inaccessible at the Tevatron but potentially testable at the LHC. The work underscores the sensitivity of precision EW data to new physics in extra dimensions and points to distinctive collider signatures for these extended models.

Abstract

Electroweak measurements place significant bounds on higher-dimensional versions of the standard model in which the gauge and Higgs fields have Kaluza-Klein excitations. These bounds may be altered quantitatively if chiral matter is also allowed to propagate in the higher-dimensional `bulk'. We determine the electroweak constraints on a number of models of this type, including scenarios in which only the leptons or only the first two generations of matter fields propagate in the bulk. We also consider the possibility that different factors of the electroweak gauge group may be distinguished by their bulk/three-brane assignment, and study a minimal extra-dimensional Z' model. We find typical bounds on the compactification scale between 1.5 and 4 TeV, and comment on models in which these bounds might be significantly relaxed.

Electroweak Constraints on Extended Models with Extra Dimensions

TL;DR

The paper investigates electroweak precision constraints on extensions of the Standard Model with extra dimensions, focusing on three representative bulk/brane assignments for gauge, Higgs, and chiral matter. It derives how Kaluza-Klein excitations and mass mixing modify electroweak observables and computes bounds on the compactification scale for δ=1, finding typical limits in the 1.5–4 TeV range while highlighting model-dependent variations. The results show that bulk leptons can yield the strongest bounds due to Z–KK mixing, SU(2)-brane scenarios are constrained mainly by G_F, and bulk generations depend strongly on the bulk vs brane Higgs vev ratio; these constraints imply that KK states are generally inaccessible at the Tevatron but potentially testable at the LHC. The work underscores the sensitivity of precision EW data to new physics in extra dimensions and points to distinctive collider signatures for these extended models.

Abstract

Electroweak measurements place significant bounds on higher-dimensional versions of the standard model in which the gauge and Higgs fields have Kaluza-Klein excitations. These bounds may be altered quantitatively if chiral matter is also allowed to propagate in the higher-dimensional `bulk'. We determine the electroweak constraints on a number of models of this type, including scenarios in which only the leptons or only the first two generations of matter fields propagate in the bulk. We also consider the possibility that different factors of the electroweak gauge group may be distinguished by their bulk/three-brane assignment, and study a minimal extra-dimensional Z' model. We find typical bounds on the compactification scale between 1.5 and 4 TeV, and comment on models in which these bounds might be significantly relaxed.

Paper Structure

This paper contains 5 sections, 53 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Bulk Leptons
  3. Bulk Generations
  4. An SU(2)-brane scenario
  5. Conclusions

Figures (1)

  • Figure 1: Bounds on the bulk generations scenario. The $h_t$ line indicates where the top quark Yukawa coupling becomes nonperturbative. The bound from $\rho$ is indistinguishable from the $\Gamma(e^+e^-)$ result.