Immediately after the Big Bang, the Universe underwent ultra-fast expansion, an idea proposed by Alan Guth and developed by Andrei Linde. When the expansion stopped, the field-energy began to oscillate like a giant swing. The rhythmic pushes of this field turned quantum jitters into real particles — and the void started filling with matter.
Precise computer modeling revealed a surprising picture. The birth of matter was uneven: short perturbations arose in sharp jumps, as if the swing was kicked randomly but forcefully; long waves grew smoothly and leisurely. This intermittent process instantly heated the Universe from near absolute zero to unimaginable temperatures. In mere moments, particles of the future Standard Model were born, and entropy — the measure of disorder — surged, setting off an irreversible path toward complexity and chaos.
as written by the authors arXiv:2604.23224
Preheating after inflation proceeds through parametric resonance, leading to efficient particle production in scalar field models. In this work, we investigate the structure of parametric resonance in the $$\phi^4$$ chaotic inflationary model during the preheating phase by performing a fully numerical analysis of the coupled dynamical equations governing the inflaton field and the mode function of the produced particles, thereby avoiding the approximations commonly employed in earlier studies. Our results reveal resonance patterns that differ significantly from those obtained with approximate analytical treatments. In the weak coupling regime, short-wavelength modes rapidly settle into oscillations with nearly constant amplitude, while the corresponding occupation numbers approach saturation. However, the long-wavelength modes exhibit gradual amplitude growth, with occupation numbers transitioning into a non-linear oscillatory regime. As the coupling strength increases, the dynamics becomes increasingly nonlinear, leading to the emergence of stochastic behavior. In the strong coupling regime, short-wavelength modes display a step-like (staircase) evolution in the occupation number, indicative of intermittent bursts of particle production. However, the long-wavelength modes exhibit a more gradual, monotonic growth with small superimposed fluctuations. These findings highlight the rich, coupling-dependent, structure of parametric resonance in the quartic inflationary model and underscore the importance of exact numerical treatment in accurately capturing preheating dynamics.
From near absolute zero after inflation, the Universe instantly heated up to unimaginable temperatures: thus began the hot Big Bang familiar to us from textbooks.