  We investigate a model with a massless fermion and a massive scalar field
with the Yukawa interaction between these two fields. The model possess a
discrete symmetry. The chiral condensate is calculated in one-loop
approximation in $(1+1)$-dimensional spacetime. It was shown that the chiral
condensate vanishes at two different values of the coupling constant. At the
first of them there is a phase transition in which the discrete symmetry is
restored. At the second zero of the chiral condensate it takes place a phase
transition which distinguishes the positive $\mu^2$ from the negative $\mu^2$,
where $\mu^2$ is an effective mass of the scalar field.

High Energy Physics - Phenomenology