Pion condensation in the two--flavor chiral quark model at finite   baryochemical potential
  Pion condensation is studied at one--loop level and nonzero baryochemical potential in the framework of two flavor constituent quark model using the one--loop level optimized perturbation theory for the resummation of the perturbative series. A Landau type of analysis is presented for the investigation of the phase boundary between the pion condensed/non-condensed phases. The statement that the condensation starts at $\muI = m_{\pi}$ is slightly modified by one--loop corrections. The second order critical surface is determined and analysed in the $\muI-\muB-T$ space. The $\muI$ dependence of the one--loop level charged pion pole masses is also studied. 
T. Herpay, P. Kov\'acs