Theta vacuum effects on QCD phase diagram
  Theta vacuum effects on the QCD phase structure in the \mu-T plane are studied by using the Polyakov-loop extended Nambu-Jona-Lasinio model and its extension, where \mu is the quark chemical potential and T is temperature, respectively. As the parameter \theta of the theta vacuum increases, the chiral transition becomes stronger. For large \theta, it eventually becomes first order even at zero \mu. 
Yuji Sakai, Hiroaki Kouno, Takahiro Sasaki and Masanobu Yahiro
hep-ph hep-lat hep-th nucl-th