Higgs Dark Matter in UEDs: A Good WIMP with Bad Detection Prospects
  We study the first Kaluza-Klein excitation of the Higgs boson in universal
extra dimensions as a dark matter candidate. The first-level Higgs boson could
be the lightest Kaluza-Klein particle, which is stable due to the conservation
of Kaluza-Klein parity, in non-minimal models where boundary localized terms
modify the mass spectrum. We calculate the relic abundance and find that it
agrees with the observed dark matter density if the mass of the first-level
Higgs boson is slightly above 2 TeV, not considering coannihilations and
assuming no relative mass splitting among the first-level Kaluza-Klein modes.
In the case of coannihilations and a non-zero mass splitting, the mass of the
first-level Higgs boson can range from 1 TeV to 4 TeV. We study also the
prospects for detection of this dark matter candidate in direct as well as
indirect detection experiments. Although the first-level Higgs boson is a
typical weakly interacting massive particle, an observation in any of the
conventional experiments is very challenging.
