Superheavy WIMP dark matter from incomplete thermalization

Although it is usually thought that a class of weakly interacting massive particle (WIMP) dark matters (DMs), which have the vector coupling with the Z boson, is denied by null results of the direct DM searches, such WIMP DMs are still viable if they are superheavy with the mass of ({m}{DM}\gtrsim {10}^{9}) GeV. In the future, the superheavy WIMP DMs can be searched up to ({m}{DM}\simeq {10}^{12}) GeV, which corresponds to the so-called neutrino floor limit. We show that the observed abundance of ({\Omega }{\text{DM}}{h}^{2}\simeq 0.1) for a superheavy WIMP DM can be reproduced by a suitable reheating temperature of ({T}{R}\simeq {m}_{DM}/29) after inflation, if the direct inflaton decay into DM is negligible or kinematically forbidden.