Massive particle pair production and oscillation in Friedman Universe: dark energy and matter interaction

The classical Friedman equations of time-varying Hubble function $H$, dark-energy and matter densities couple to quantised field equations for massive modes $M\gg H$. Numerically solving these equations, we show the particle-antiparticle pairs production and oscillation in microscopic time scale ${\mathcal O}(M^{-1})$. A massive pair plasma state is formed in macroscopic time scale ${\mathcal O}(H^{-1})$. Its density and pressure introduce the interaction of matter and dark energy densities in the Friedman equations. Focusing on epochs after reheating, we show that the negative dark energy tracks down the radiation energy in the radiation epoch. Such tracking dynamics ends, and dark energy becomes positive in the matter epoch. The matter converts to dark energy, and their present values are comparable, explaining the cosmic coincidence. As a result, a class of effective interacting dark energy models is advocated to confront cosmological observations.