Deeply bound pionic states and the effective pion mass in nuclear systems

We show that the s-wave pion-nuclear potential which reproduces the deeply bound pionic states in Pb, recently discovered at GSI, is remarkably close to the one constructed directly from low energy theorems based on chiral symmetry. Converting this information into an effective pion mass we find $m_{\pi }^{\star }\mathrm{/}{m}_{\pi }\simeq 1.13$ in the center of the Pb nucleus, and $m_{\pi }^{\star }\mathrm{/}{m}_{\pi }\simeq 1.07$ in symmetric nuclear matter.