  Multidimensional modification of gravity with a smaller mass scale of the
gravitational interaction is considered. Stable by assumption dark matter
particles could decay via interactions with virtual black holes. The decay
rates of such processes are estimated. It is shown that with the proper
fixation of the parameters the decays of these ultra-massive particles can give
noticeable contribution to the flux of high energy cosmic rays in particular,
near the Greisen-Zatsepin-Kuzmin limit. Such particles can also create
neutrinos of very high energies observed in the existing huge underwater or
ice-cube detectors.
