Annihilations of superheavy dark matter in superdense clumps
  Superheavy dark matter (SHDM) exchanges energy with its environment much
slower than particles with masses close to the electroweak (EW) scale and has
therefore different small-scale clustering properties. Using the neutralino as
candidate for the SHDM, we find that free-streaming allows the formation of DM
clumps of all masses down to $\sim 260 m_\chi$ in the case of bino. If
small-scale clumps evolve from a non-standard, spiky spectrum of perturbations,
DM clumps may form during the radiation dominated era. These clumps are not
destroyed by tidal interactions and can be extremely dense. In the case of a
bino, a "gravithermal catastrophe" can develop in the central part of the most
dense clumps, increasing further the central density and thus the annihilation
signal. In the case of a higgsino, the annihilation signal is enhanced by the
Sommerfeld effect. As a result annihilations of superheavy neutralinos in dense
clumps may lead to observable fluxes of annihilation products in the form of
ultrahigh energy particles, for both cases, higgsinos and binos, as lightest
supersymmetric particles.
