  In this paper we calculate the effective action for neutral particles with
anomalous magnetic moment in an external magnetic and electric field. We show
that we can take advantage from the Foldy Wouthuysen transformation for such
systems, determined in our previous works: indeed, by this transformation we
have explicitly evaluated the diagonalized Hamiltonian, allowing to present a
closed form for the corresponding effective action and for the partition
function at finite temperature from which the thermodynamical potentials can be
calculated.
