Large Deviation of the Density Profile in the Steady State of the Open Symmetric Simple Exclusion Process

We consider an open one dimensional lattice gas on sites i=1,..., N, with particles jumping independently with rate 1 to neighboring interior empty sites, the simple symmetric exclusion process. The particle fluxes at the left and right boundaries, corresponding to exchanges with reservoirs at different chemical potentials, create a stationary nonequilibrium state (SNS) with a steady flux of particles through the system. The mean density profile in this state, which is linear, describes the typical behavior of a macroscopic system, i.e., this profile occurs with probability 1 when NQ.. The probability of microscopic configurations corresponding to some other profile r(x), x=i/N, has the asymptotic form exp[−NF({r})]; F is the large deviation functional. In contrast to equilibrium systems, for which Feq({r}) is just the integral of the appropriately normalized local free energy density, the F we find here for the nonequilibrium system is a nonlocal function of r. This gives rise to the long range correlations in the SNS predicted by fluctuating hydrodynamics and suggests similar nonlocal behavior of F in general SNS, where the long range correlations have been observed experimentally.