Dynamics of broken symmetry λφ4 field theory -: art. no. 051901

We study the domain of validity of a Schwinger-Dyson approach to nonequilibrium dynamics when [phi(x)] not equal 0. We perform exact numerical simulations of the one- and two-point functions of a single component lambdaphi(4) field theory in 1 + 1 dimensions in the classical field theory case. We compare these results to two self-consistent truncations of the Schwinger-Dyson equations which ignore three-point vertex function corrections. The first approximation, which we called the bare vertex approximation, sets the three-point function to one. It gives a promising description for [phi(x)] = phi(t). The second approximation, which ignores higher in 1/N corrections to the 2PI generating functional is not as accurate for phi(t) for the case N = 1. Both approximations have serious deficiencies in describing the two-point function when phi(0)greater than or similar to0.4.