  Statistical theory of the dielectric susceptibility of polar liquid crystals
is proposed. The molecules are calamitic or bent-core but the permanent dipole
moment is perpendicular to the molecule long axis. The ordering of the phase is
described by means of the mean-field theory based on the Maier-Saupe approach.
The theory is used to calculate the temperature dependence of the order
parameters and the susceptibilities. The phase diagram with four phases is
obtained: isotropic, uniaxial nematic, uniaxial ferroelectric, and biaxial
ferroelectric. Four critical points are predicted.
