Accelerated expansion in the effective field theory of a radiation dominated universe

We construct the effective field theory of a perfect fluid in the early Universe. Focusing on the case where the fluid has the equation of state of radiation, we show that it may lead to corrections to the background dynamics that can dominate over those of an effective field theory of gravity alone. We describe the periods of accelerated expansion, in the form of inflationary and bounce solutions, that arise in the background dynamics and discuss their regime of validity within effective field theory.

Figure 1

Plot of solutions of Eq. (7): “EFT - A,” Eq. (9): “EFT - B,” and of the classical FLRW solution: “FLRW,” where we have set $M_P={\rho }_0=M=1$ and $A=B=0.05$ for clarity (this rescaling does not satisfy ${\rho }_0\ll M_P^4$ or $M\ll M_P$; however this will not change the behavior of the solution but only make this new behavior more evident). The time scale corresponds to one Hubble time ($1/H_0$) in the rescaled units, and the scale for $a$ corresponds to $a(1/H_0)$. Note that at late times all solutions approach the classical solution for a radiation dominated universe.