  The Universal Extra Dimensions model has been implemented in the Pythia
generator from version 6.4.18 onwards, in its minimal formulation with one
inverse-TeV-sized extra dimension. The additional possibility of
gravity-mediated decays, through a variable number of inverse-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
iso-doublet and -singlet KK excitations is neglected thus far, and is expected
to be negligible for all but the top sector.
