Neutron-proton mass difference in nuclear matter U. -G. Meißner, A. M. Rakhimov, A. Wirzba and U. T. Yakhshiev Eur. Phys. J. A, 31 3 (2007) 357-364 Published online: 12 March 2007 DOI: 10.1140/epja/i2006-10274-6