  Partition function zeros provide alternative approach to study phase
structure of finite density QCD. The structure of the Lee-Yang edge
singularities associated with the zeros in the complex chemical potential plane
has a strong influence on the real axis of the chemical potential. In order to
investigate what the singularities are like in a concrete form, we resort to an
effective theory based on a mean field approach in the vicinity of the critical
point. The crossover is identified as a real part of the singular point. We
consider the complex effective potential and explicitly study the behavior of
its extrema in the complex order parameter plane in order to see how the Stokes
lines are associated with the singularity. Susceptibilities in the complex
plane are also discussed.
