η' meson under partial restoration of chiral symmetry in nuclear medium*

Abstract

We shed light upon the η' mass in nuclear matter in the context of partial restoration of chiral symmetry, pointing out that the UA(1) anomaly effects causes the η'-η mass difference necessarily through the chiral symmetry breaking. As a consequence, it is expected that the η' mass is reduced by order of 100 MeV in nuclear matter where partial restoration of chiral symmetry takes place. The discussion given here is based on Ref. [1]