CLASSICAL NATURE OF THE INFLATION FIELD WITH SELF-INTERACTION

Taking into account the effect of self-interaction, the dynamics of th e quantum fluctuations of the inflaton field with a lambda phi(4) pote ntial is studied in detail. We find that the self-interaction efficien tly drives the initial pure state into a mixed state, which can be und erstood as a statistical ensemble. Further, the expectation value of t he squared field operator is found to be converted into the variance o f this statistical ensemble without giving any significant change in t he amplitude of fluctuations. These results verify the ansatz of the q uantum-to-classical transition that has been assumed in the standard e valuation of the amplitude of the primordial fluctuations of the unive rse.