  We study the competition between the Kondo effect and the exchange
interaction in the parallel double quantum dot(DQDs) system within an effective
action field theory. The strong on-site Coulomb interactions in DQDs are
treated by using the Hubbard-Stratonovich transformation and the introduction
of scalar potential fields. We show that a self-consistent perturbation
approach, which takes into account the statistical properties of the potential
fields acting on the electrons in DQDs, describes well the crossover from the
Kondo regime to the spin-singlet state in this system. The linear conductance
and the intradot/interdot spin excitation spectra of this system are obtain
