Possible medium effects on \eta-\pi^0 mixing and \eta \rightarrow \pi^0   \pi^+ \pi^- decay in the asymmetric nuclear matter
  It is known that the decay process \eta\rightarrow\pi^0\pi^+\pi^- in free space is possible due to the isospin-symmetry breaking in Quantum Chromodynamics (QCD), i.e., the small mass difference between u and d quarks: The small width is intimately related with the mixing property between \eta and \pi^0 mesons for which the chiral anomaly play a role. In asymmetric nuclear matter such as heavy nuclei, isospin-symmetry breaking is large and it is expected that the mixing property of the mesons changes significantly and the above-mentioned decay width of the \eta created in such a medium may be enhanced. This is an intriguing possibility to revealing a medium effect on a hadron in nuclei. We apply the in-medium chiral perturbation theory to estimate the modification of the \eta -\pi^0 mixing angle and the partial width of \eta\pi^0\pi^+\pi^- in asymmetric nuclear matter as a function of the isospin asymmetry. We find that these quantities can be greatly enhanced in neutron-rich matter, which should be deteactable in experiment. 
Shuntaro Sakai, Teiji Kunihiro
hep-ph nucl-th