Stochastic Gravitational Waves from Preheating

Ritwik, Piduri (2025) Stochastic Gravitational Waves from Preheating. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Piduri Ritwik (20MS227)) 20MS227_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (7MB)

Abstract

This thesis explores the generation and evolution of stochastic gravitational waves (GWs) sourced during the preheating phase following cosmic inflation. Focusing on two canonical inflaton potentials, the quartic potential V (ϕ) = λ 4ϕ4 and the quadratic potential V (ϕ) = 1 2m2ϕ2, we investigate how explosive particle production via parametric resonance leads to the generation of GWs. After reviewing the linearized theory of GW propagation and the role of the anisotropic stress tensor as a source, we analyze both the analytical scaling behavior of the resulting GW spectra and the influence of key parameters such as the resonance parameter q and inflaton mass mϕ. Using numerical simulations performed with the CosmoLattice package, we study the time evolution and spectral characteristics of the GWs produced. Our results confirm analytical predictions for the scaling of peak amplitude ΩGW ∝ q−1/2 and peak momentum kp ∝ q1/4 during the linear regime, with deviations observed in the fully non-linear phase. We also find that in the quartic case, two infrared peaks emerge independently of q, while for the quadratic potential, the GW amplitude increases with inflaton mass but the peak momentum remains fixed, highlighting a decoupling between frequency and coupling strength. These findings provide a detailed understanding of how early-universe dynamics imprint unique signatures on the stochastic GW background.

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