One universal extra dimension in Pythia

The Universal Extra Dimensions model has been implemented in the PYTHIA generator from version 6.4.18 onwards, in its minimal formulation with one TeV sized extra dimension. The additional possibility of gravity-mediated decays, through a variable number of eV sized extra dimensions into which only gravity extends, is also available. The implementation covers the lowest lying Kaluza-Klein (KK) excitations of Standard Model particles, except for the excitations of the Higgs fields, with the mass spectrum calculated at one loop. 2 → 2 tree-level production cross sections and KK number conserving 2-body decays are included. Mixing between isodoublet and -singlet KK excitations is neglected thus far, and is expected to be negligible for all but the top sector.