Decoding the phases of early and late time reheating through imprints on primordial gravitational waves

Understand

Primordial gravitational waves (GWs) carry the imprints of the dynamics of the universe during its earliest stages.

• With a variety of GW detectors being proposed to operate over a wide range of frequencies, there is great expectation that observations of primordial GWs can provide us with an unprecedented window to the physics operating during inflation and reheating.
• In this work, we closely examine the effects of the regime of reheating on the spectrum of primordial GWs observed today.
• We consider a scenario wherein the phase of reheating is described by an averaged equation of state (EoS) parameter with an abrupt transition to radiation domination as well as a scenario wherein there is a gradual change in the effective EoS parameter to that of radiation due to the perturbative decay of the inflaton.