The experimental detection of gravitational waves (GWs) due to the merger of astrophysical objects like black holes and neutron stars is one of the biggest discoveries in physics. The GWs can also be sourced from several other cosmological phenomena, and their amplitudes and frequencies vary in a wide range. The detection of these gravitational waves can potentially probe fundamental physics beyond the Standard Model (BSM) of particle physics and cosmology. For example, inflation is associated with several sources of tensor perturbations during inflation and the ones generated during reheating and preheating. Each of these propagates as detectable Stochastic GW background (SGWB) signals. Associated with inflation is also the collapse of density fluctuations to form Primordial Black Holes (PBH), leaving signatures in induced GWs and non-gaussianities. Cosmological first-order Phase Transitions (PT) during which the universe transitions from a false vacuum to a true vacuum leads to bubbl...
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