Resonances from Two Universal Extra Dimensions

TL;DR

This work analyzes the Standard Model with two universal extra dimensions compactified on the chiral square, showing that (1,1) KK vector modes can be singly produced and yield a predictable pattern of narrow t tbar resonances, while spinless adjoints enrich the phenomenology. The authors derive the KK mass spectrum, KK-number violating couplings, and detailed branching fractions for all (1,1) modes, highlighting distinctive collider signatures. They quantify Tevatron s-channel production prospects, including multiple closely spaced ttbar resonances, and project LHC reach for higher 1/R through ttbar and dijet channels, underscoring the potential to test a clustered KK-spectrum from two universal extra dimensions. The study also notes a viable dark matter candidate among the spinless adjoints, connecting collider signals to cosmological implications in a unified 6D framework.

Abstract

Standard model gauge bosons propagating in two universal extra dimensions give rise to heavy spin-1 and spin-0 particles. The lightest of these, carrying Kaluza-Klein numbers (1,0), may be produced only in pairs at colliders, whereas the (1,1) modes, which are heavier by a factor of \sqrt{2}, may be singly produced. We show that the cascade decays of (1,1) particles generate a series of closely-spaced narrow resonances in the t\bar{t} invariant mass distribution. At the Tevatron, s-channel production of (1,1) gluons and electroweak bosons will be sensitive to t\bar{t} resonances up to masses in the 0.5 - 0.7 TeV range. Searches at the LHC for resonances originating from several higher-level modes will further test the existence of two universal extra dimensions.

Figures (9)

• Figure 1: Mass spectrum of the (1,1) level for $1/R$ = 500 GeV. Electroweak symmetry breaking effects are small, and have not been included.
• Figure 2: Mass spectrum of the (1,0) level. The lightest KK particle is the $B_H^{(1,0)}$ spinless adjoint.
• Figure 3: Production cross sections for $(1,1)$ vector modes in the $s$ channel at the Tevatron, as a function of their mass. The solid line is for $G^{(1,1)}_\mu$, while the dashed and dotted (lowest) lines are for $W^{(1,1)3}_\mu$ and $B^{(1,1)}_\mu$, respectively (accidentally, the cross sections for these two are close to each other such that they might not be distinguishable).
• Figure 4: Production of the vector (1,1) gluon followed by a cascade decay. The $\bullet$ stands for a KK number-violating coupling. Other diagrams having the same topology exist: the $U_-^{(1,1)}$ quark KK mode may be replaced by $D_-^{(1,1)}$, $Q_+^{(1,1)}$, or the corresponding anti-quarks; in addition the spinless gluon $G^{(1,1)}_H$ may be replaced by $B^{(1,1)}_\mu$ or $B^{(1,1)}_H$, and in the case where the quark KK mode is an $SU(2)_W$ doublet, by $W^{(1,1)3}_\mu$ or $W^{(1,1)3}_H$.
• Figure 5: Production of $W^3_\mu$ and $B_\mu$ (1,1) modes, followed by representative decays.