Inflation with generalized initial conditions

In many current models of the early Universe a scalar field φ which is only very weakly coupled to other quantum fields is used to generate inflation. In such models there are no forces which could thermalize the scalar field, and previous assumptions about its preinflation ‘‘initial’’ conditions must be abandoned. In this paper the onset of inflation is studied classically for more general initial conditions of the scalar field configuration. In particular, initial conditions with a nonvanishing spatial average of φ, with φ chosen at random in each initial horizon volume, and with random initial momenta are considered. We identify and discuss several mechanisms that can drive these more general initial conditions toward an inflationary state. The analysis is done in one spatial dimension.