Universal extra dimensions after Higgs discovery

Abstract

We show bounds on five-and six-dimensional universal extra dimension (UED) models from the latest results of the Higgs searches at the LHC and from the electroweak precision data for the S and T parameters. We consider the minimal UED model in five dimensions and the ones in six dimensions, compactified on T 2 /Z 2 , T 2 /(Z 2 × Z 2 ), T 2 /Z 4 , S 2 , S 2 /Z 2 , the real projective plane, and the projective sphere. The highest possible ultraviolet cutoff scale for each UED model is evaluated from the electroweak vacuum stability by solving the renormalization group equation of the Higgs self-coupling. This scale turns out to be lower than the conventional one obtained from the perturbativity of the gauge coupling. The resultant 95% C.L. lower bounds on the first Kaluza-Klein scale from the LHC results and from the S, T analysis are 600 and 700 GeV in the minimal UED model, while those in the six-dimensional UED models are 800-1300 GeV and 900-1500 GeV, respectively.

A review on non-minimal universal extra dimensions

“…current bound on the MUED model lies at R −1 > 680 GeV [35,36] and results mostly from the loop contributions of the KK top and Higgs modes to the gauge boson propagators. In non-minimal extensions, boundary terms and quark bulk masses lift the degeneracy of the KK mass spectrum.…”

“…UED models predict an enhanced Higgs production rate via gluon fusion as well as a modified decay rate for h → γγ because the top KK modes and (for the decay) W KK modes contribute to these one-loop induced processes [36,38,39]. Within the minimal UED model, the current ATLAS and CMS Higgs measurements [40,41] imply a lower bound of R −1 460GeV (from ATLAS data) and R −1 1300GeV (from CMS data) [42].…”

Status report on universal extra dimensions after LHC8

“…Due to additional KK loops, in particular the KK top, Higgs production is enhanced in UED while the Higgs to diphoton branching fraction also receives contributions from the KK W and is suppressed with respect to the SM prediction 48 . However, the corresponding bounds on the KK mass scale are much weaker than those from direct production of KK quarks and gluons, of the order of 600 GeV for MUED 49,13 . …”

“…Here 1-loop stands f couplings between level 2 and SM particles. The shaded region correspond preferred region obtained by WMAP [13].…”

“…680 GeV 12,13 . Besides, the flavor structure of the bulk lagrangian, being the same as the SM one, includes the GIM mechanism.…”