Particle-antiparticle oscillation modes crossing horizon: Baryogenesis and dark-matter waves

Quantum massive particle and antiparticle pair production and oscillation during reheating result in a holographic and massive pair plasma state. Perturbations in the densities of particles and antiparticles within this plasma form acoustic waves, characterized by symmetric and asymmetric density contrasts. By deriving the acoustic wave equations and identifying the frequencies of the lowest-lying perturbation modes (with zero wave number), the study shows that the wavelengths of these modes, when compared with the horizon size, suggest the possibility of superhorizon crossing during reheating. This crossing leads to particle-antiparticle asymmetry observable by an observer inside the horizon. The decay of massive particles and antiparticles into baryons generates a net baryon number, potentially explaining baryogenesis. The calculated baryon number-to-entropy ratio aligns with observational data. This crossing also accounts for dark matter particle-antiparticle asymmetry in the present Universe. The study also explores perturbation modes with nonzero wave numbers, representing dark-matter acoustic waves. These modes exited the horizon and re-entered after recombination, potentially imprinting on the matter power spectrum at large length scales and influencing the formation of large-scale structures and galaxies.