Theory HEP Seminar

Primordial black holes, dark matter and gravitational waves as a probe of the early universe

Riajul Haque

IIT Madras

I will start my talk with a brief overview of the standard reheating scenario. If Primordial Black Holes (PBHs) are formed during the reheating epoch due to the enhancement of the primordial scalar power spectrum on small scales, such primordial spectra also inevitably lead to strong amplification of the scalar-induced secondary gravitational waves (GWs) at higher frequencies. I will show how the recent detection of the stochastic gravitational wave background (SGWB) by the pulsar timing arrays (PTAs) has opened up the possibility of directly probing the very early universe through the scalar-induced secondary gravitational waves. Then, I will discuss reheating through the evaporation of the ultra-light PBHs. In addition, I will show the dark matter parameter space produced from evaporating PBHs in the background of reheating obtained from two chief systems in the early universe: the inflaton and the PBHs. If Ultra-light PBHs, briefly dominating the universe's expansion, would leave detectable imprints in the SGWB. Such a scenario leads to a characteristic doubly peaked spectrum of SGWB and strongly depends on the background equation of state where it forms. Finally, I will conclude my talk by elaborating on the effect of quantum correction on the Hawking radiation for ultra-light PBHs and its observational signature through dark matter and gravitational waves.

References: Phys.Rev.D 108 (2023) 6, 063523; Phys.Rev.D 109 (2024) 2, 023521; e-Print: 2403.16963 (Accepted in JCAP);  JCAP 07 (2024) 002, and JHEP 10 (2024) 142.