Mixed dark matter in Universal Extra Dimension models with TeV scaleWRandZ′

We show that in a class of universal extra dimension (UED) models that solvesboth the neutrino mass and proton decay problems using low scale left-rightsymmetry, the dark matter of the Universe consists of an admixture of KK photonand KK right-handed neutrinos. We present a full calculation of the dark matterdensity in these models taking into account the co-annihilation effects due tonear by states such as the scalar partner of the KK photon as well as fermionstates near the right-handed KK neutrino. Using the value of the relic CDMdensity, we obtain upper limits on $R^{-1}$ of about 400-650 GeV and$M_{Z'}\leq 1.5$ TeV, both being accessible to LHC. For a region in thisparameter space where the KK right-handed neutrino contributes significantly tothe total relic density of dark matter, we obtain a lower bound on the darkmatter-nucleon scattering cross section of $10^{-44}$ cm$^2$, which can beprobed by the next round of dark matter search experiments.Comment: 28 pages, 7 figure