The phase structure of two-flavor QCD is investigated at real isospin and
imaginary quark chemical potentials by using the Polyakov-loop extended
Nambu--Jona-Lasinio model. In the region, parity symmetry is spontaneously
broken by the pion superfluidity phase transition, whereas charge-conjugation
symmetry is spontaneously violated by the Roberge-Weiss transition. The chiral
(deconfinement) crossover at zero isospin and quark chemical potentials is a
remnant of the parity (charge-conjugation) violation. The interplay between the
parity and charge-conjugation violations are analyzed, and it is investigated
how the interplay is related to the correlation between the chiral and
deconfinement crossovers at zero isospin and quark chemical potentials.Comment: 12 pages, 18 figures. Typos were revised. Symbols /P and /C were
added in Figures 8a and 8b. Colors of the figures were changed. Some
sentences were added and revise