Gravitational dark matter from minimal preheating

Following our previous work, we continue to explore gravitational dark matter production during the minimal preheating caused by inflaton self-resonance. In this situation there is only one dimensionless index parameter n characterizing the inflation potential after the end of inflation, which leads to a robust prediction on the gravitational dark matter relic abundance. Using lattice method to handle the non-perturbative evolutions of relevant quantities during the inflaton self-resonance, we derive the gravitational dark matter relic abundance arising from both the inflaton condensate and fluctuation annihilation. While being absent in the large gravitational dark matter mass range for n = 2, the former one can instead dominate over the later one for n = 4, 6. Our results show that gravitational dark matter mass of 1.04 (2.66) × 10¹⁴ GeV accommodates the observed value of dark matter relic abundance for n = 4 (6).