  Charge conjugation (C) and Parity (P) are exact symmetries at theta =pi and
Theta = mu/(iT)=pi, where theta is the parameter of the so-called theta-vacuum,
mu is the imaginary quark-number chemical potential and T is the temperature.
Spontaneous breakings of these discrete symmetries are investigated by the the
Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model. At zero T, P symmetry
is spontaneously broken while C symmetry is conserved. As T increases, P
symmetry is restored just after C symmetry is spontaneously broken, so that
either P or C symmetry or both the symmetries are spontaneously broken for any
T. The chiral-symmetry restoration and the deconfinement transition at theta
=Theta =0 are remnants of the P restoration and the C breaking at theta =Theta
=pi, respectively.
