Self-sustained, out-of-equilibrium inflation

We use holography to study dS-invariant states of non-conformal, strongly coupled quantum field theories in four-dimensional de Sitter space. We show that out-of-equilibrium effects can sustain the exponential inflation within the regime of validity of semiclassical gravity, $H \ll M \ll M_\mathrm{sp}$, with $H$ the Hubble parameter, $M$ the characteristic scale of the quantum field theory, $M_\mathrm{sp} = M_\mathrm{p}/N$ the species scale, $M_\mathrm{p}$ the Planck scale, and $N^2$ the number of matter fields. In the holographic description, the required fine-tuning scales only logarithmically with the ratio $M_\mathrm{sp}/H$. The resulting solutions exhibit apparent horizons whose increasing area indicates a continuous growth of the comoving entropy density. We suggest that this inflationary regime can arise as the late-time limit of a dynamical evolution starting from an initial Friedmann-Lema\^itre-Robertson-Walker universe.