A renewed look at eta' in medium
  We revisit the question of whether the U_A(1) symmetry is effectively restored in hot and dense medium. In particular, by generalizing the Witten-Veneziano formula to finite temperature, we investigate whether the mass of eta'-meson will change in medium due to the restoration of chiral symmetry. 
Youngshin Kwon, Su Houng Lee, Kenji Morita, Gyuri Wolf
nucl-th hep-lat hep-ph