On thermal gravitational contribution to particle production and dark matter

Abstract

We investigate the particle production from thermal gravitational annihilation in the very early universe, which is an important contribution for particles that might not be in thermal equilibrium or/and might only have gravitational interaction, such as dark matter (DM). For particles with spin 0, 1/2 and 1 we calculate the relevant cross sections through gravitational annihilation and give the analytic formulas with full mass-dependent terms. We find that DM with mass between TeV and 10 16 GeV could have the relic abundance that fits the observation, with small dependence on its spin. We also discuss the effects of gravitational annihilation from inflatons. Interestingly, contributions from inflatons could be dominant and have the same power dependence on Hubble parameter of inflation as that from vacuum fluctuation. Also, fermion production from inflaton, in comparison to boson, is suppressed by its mass due to helicity selection.

Production of purely gravitational dark matter: the case of fermion and vector boson

“…Evidently, wide parameter space exists for the correct DM relic density. Note that we should also include the contribution from thermal production by gravitational annihilation of SM particles in the thermal bath [18][19][20][21]. See Appendix C for details.…”

“…Here we briefly summarize the thermal production (TP) of gravitationally interacting DM. The production cross section of purely gravitational DM X, either X is fermion or vector boson, through the scattering of SM particles in the thermal bath with the temperature T is [18][19][20][21] σv = y T 2 M 4 P for T > m X ,…”

“…#2 Gravitationally interacting particles are also produced by scatterings of the Standard Model (SM) particles in thermal bath through the graviton exchange [18][19][20][21].…”

Misalignment & Co.: (pseudo-)scalar and vector dark matter with curvature couplings

“…The focus of the studies has been on the generation of dark matter during inflation [42][43][44][45][46][47] or at preheating and reheating [64][65][66][67][68][69][70][71][72]. Graviton-mediated thermal production has also been explored [70][71][72][73][74][75][76].…”

A note on gravitational particle production in supergravity

“…In such a case the fermion contribution is negligible and the slow contribution to the scalar production should be taken into account. Then the moduli abundance is expected to be given by (46) after m χ is reinterpreted as the SUSY breaking moduli mass and ∆ replaced #8 One also should take into account the contribution from gravitational scattering of MSSM particle in thermal bath that create χ particles [36][37][38][39].…”