Precise calculation of the relic density of Kaluza-Klein dark matter in universal extra dimensions

We revisit the calculation of the relic density of the lightest Kaluza-Kleinparticle (LKP) in the model of Universal Extra Dimensions. The Kaluza-Klein(KK) particle spectrum at level one is rather degenerate, and variouscoannihilation processes may be relevant. We extend the calculation ofhep-ph/0206071 to include coannihilation processes with all level one KKparticles. In our computation we consider a most general KK particle spectrum,without any simplifying assumptions. In particular, we do not assume acompletely degenerate KK spectrum and instead retain the dependence on eachindividual KK mass. As an application of our results, we calculate theKaluza-Klein relic density in the Minimal UED model, turning on coannihilationswith all level one KK particles. We then go beyond the minimal model anddiscuss the size of the coannihilation effects separately for each class oflevel 1 KK particles. Our results provide the basis for consistent relicdensity computations in arbitrarily general models with Universal ExtraDimenions.Comment: 44 pages, 19 figures, typeset in JHEP styl