Dr. Swagat Saurav Mishra

The transition from cosmic inflation to the hot Big Bang, known as reheating, remains a key open question in cosmology. During its early stage, called preheating, the inflaton field decays explosively via parametric resonance into lighter bosonic offspring fields. However, when these external couplings are weak, strong self-interaction (cohesive force) causes the oscillating inflaton condensate to fragment, forming extremely long-lived scalar-field lumps known as oscillons. In this seminar, we investigate the conditions for oscillon formation during preheating, particularly in the presence of external couplings, within the class of inflationary potentials favored by the latest CMB observations. Using high-resolution (3+1)-dimensional lattice simulations on Cosmo Lattice platform, we systematically map the parameter space that supports oscillon formation. Our results suggest that preheating may have proceeded through both oscillon decay and the conventional decay of the inflaton condensate, offering new insights into the early reheating dynamics and the emergence of the hot Big Bang. The talk will conclude by highlighting ongoing efforts to connect this pre-hot Big Bang physics to the upcoming observational probes.