Resonant high energy graviton to photon conversion at post recombination epoch

Understand

Resonant conversion of high energy gravitons into photons in large scale cosmological magnetic fields at the post recombination epoch is considered.

• It is shown that the probability of the resonance photon production is much higher than the non-resonant one.
• As a result an observable isotropic background of cosmic gamma rays might be created.
• As shown in our previous paper, an early population of primordial black holes (PBHs) prior to big bang nucleosynthesis (BBN) could be an efficient source of high frequency gravitational waves.