Bosonic Supersymmetry? Getting Fooled at the LHC

TL;DR

This work introduces Minimal Universal Extra Dimensions (MUEDs), where all SM fields propagate in a single TeV-scale extra dimension and a conserved KK parity yields a stable LKP, $\gamma_1$, resulting in missing-energy signatures with soft visible objects. The authors define MUEDs with three free parameters $\{R,\Lambda,m_h\}$ and compute a one-loop corrected KK spectrum, showing a characteristic mass hierarchy and level-1 decays that resemble supersymmetric scenarios with near-degenerate spectra. They analyze collider signatures, finding that while level-1 KK states at the LHC mimic SUSY signals and are challenging to detect due to soft final states, multilepton channels and the presence of higher-level KK modes offer potential discovery avenues, with a reach up to $R^{-1} \approx 1.5$ TeV in favorable channels. They also show that level-2 KK states can provide clean probes via KK-number-violating decays to SM particles, offering additional discovery channels and a natural smoking gun for MUEDs, with the $\gamma_1$ LKP potentially serving as dark matter.

Abstract

We define a minimal model with Universal Extra Dimensions, and begin to study its phenomenology. The collider signals of the first KK level are surprisingly similar to those of a supersymmetric model with a nearly degenerate superpartner spectrum. The lightest KK particle (LKP) is neutral and stable because of KK-parity. KK excitations cascade decay to the LKP yielding missing energy signatures with relatively soft jets and leptons. Level 2 KK modes may also be probed via their KK number violating decays to Standard Model particles. In either case we provide initial estimates for the discovery potential of the Tevatron and the LHC.

Figures (4)

• Figure 1: One-loop corrected mass spectrum of the first KK level in MUEDs for $R^{-1}=500$ GeV, $\Lambda R = 20$ and $m_h=120$ GeV.
• Figure 2: Radiative corrections (in %) to the spectrum of the first KK level for $R^{-1}=500$ GeV, versus $\Lambda R$.
• Figure 3: Qualitative sketch of the level 1 KK spectroscopy depicting the dominant (solid) and rare (dotted) transitions and the resulting decay product.
• Figure 4: Discovery reach for MUEDs at the Tevatron (blue) and the LHC (red) in the $4\ell\not \!\! E_T$ channel. We require a $5\sigma$ excess or the observation of 5 signal events, and show the required total integrated luminosity per experiment (in ${\rm fb}^{-1}$) as a function of $R^{-1}$, for $\Lambda R=20$. (In either case we do not combine the two experiments).