The Phenomenology of Universal Extra Dimensions at Hadron Colliders

TL;DR

The work analyzes collider phenomenology of universal extra dimensions where all SM matter propagates in one extra dimension, enforcing KK parity that yields pair production and a stable LKP (gamma^*). It derives the 4D effective theory, computes pair-production rates, and assesses radiative corrections that split KK masses, then introduces gravity in the fat-brane framework to study gravity-mediated decays and single KK production. The study identifies distinct collider signatures—jets plus missing energy, diphoton plus MET, and multilepton final states—whose relative importance depends on the number of extra dimensions $N$, the gravity scale $M_D$, and the compactification scale $1/R$. These results highlight rich phenomenology with practical implications for Tevatron and LHC searches and offer strategies to distinguish UED from SUSY and other extra-dimensional scenarios.

Abstract

Theories with extra dimensions of inverse TeV size (or larger) predict a multitude of signals which can be searched for at present and future colliders. In this paper, we review the different phenomenological signatures of a particular class of models, universal extra dimensions, where all matter fields propagate in the bulk. Such models have interesting features, in particular Kaluza-Klein (KK) number conservation, which makes their phenomenology similar to that of supersymmetric theories. Thus, KK excitations of matter are produced in pairs, and decay to a lightest KK particle (LKP), which is stable and weakly interacting, and therefore will appear as missing energy in the detector (similar to a neutralino LSP). Adding gravitational interactions which can break KK number conservation greatly expands the class of possible signatures. Thus, if gravity is the primary cause for the decay of KK excitations of matter, the experimental signals at hadron colliders will be jets + missing energy, which is typical of supergravity models. If the KK quarks and gluons decay first to the LKP, which then decays gravitationally, the experimental signal will be photons and/or leptons (with some jets), which resembles the phenomenology of gauge mediated supersymmetry breaking models.

Figures (10)

• Figure 1: Tevatron Run I (left) and Run II (right) production rates for KK pairs. (The solid line is the total cross section, while the dotted, dashed and dot-dashed lines correspond to different types of final states, as described in the text).
• Figure 2: LHC production rates for KK pairs. (The solid line is the total cross section, while the dotted, dashed and dot-dashed lines correspond to different types of final states, as described in the text).
• Figure 3: Mass distribution (left) and energy distribution (right) for the graviton radiated in the decay of one matter KK excitation with mass 1 TeV. Straight lines corresponds to $N=2$ extra dimensions, dashed lines to $N=4$, and dotted lines to $N=6$. The integral of the area under the individual curves is equal to 1.
• Figure 4: Decay widths for KK fermions (left) and bosons (right) as a function of the particle mass. Straight lines corresponds to $N=2$ extra dimensions, dashed lines to $N=4$, and dotted lines to $N=6$. Here $M_D$ is taken to be 5 TeV.
• Figure 5: Regions in the parameter space where decays to $\gamma^*$ dominate versus the gravitational decays for $q^*, g^*$. The solid, dashed and dotted lines correspond to $N$ = 6, 4 and 2 extra dimensions.