Electromagnetic Response of Stochastic High-Frequency Gravitational Waves from Inflaton Decay

This paper concerns the production of a high-frequency stochastic gravitational wave background (SGWB) generated during the reheating epoch through gravitational decays of the inflaton field. Our analysis focuses on scenarios in which the inflaton predominantly decays into pairs of vector particles. Within this framework, we find that the resulting gravitational wave (GW) energy density spectrum exhibits a peak amplitude in the range of 10−8 to 10−6. The corresponding GW strain amplitude spans from 10−33.3 to 10−30 across the high-frequency band of 108–1011 Hz. To assess detectability, we consider the electromagnetic (EM) detection scheme and derive the associated transverse perturbative photon flux (PPF) and the signal-to-noise ratio (SNR). Our results demonstrate that both the PPF and the SNR generated by this SGWB exceed those predicted for relic GWs from canonical single-field slow-roll inflation by approximately four to five orders of magnitude. This significant enhancement suggests that high-frequency stochastic gravitational waves (HFSGWs) produced during reheating provide a more promising target for experimental detection. Our findings highlight the potential of electromagnetic (EM) detection methods as viable probes of early-universe dynamics beyond the standard inflationary paradigm.