Superheavy Dark Matter and Thermal Inflation

The thermal inflation is the most plausible mechanism that solves the cosmological moduli problem naturally. We discuss relic abundance of superheavy particle $X$ in the presence of the thermal inflation assuming that its lifetime is longer than the age of the universe, and show that the long-lived particle $X$ of mass $10^{12}$--$10^{14}$ GeV may form a part of the dark matter in the present universe in a wide region of parameter space of the thermal inflation model. The superheavy dark matter of mass $\sim 10^{13}$ GeV may be interesting in particular, since its decay may account for the observed ultra high-energy cosmic rays if the lifetime of the $X$ particle is sufficiently long.