Neutron-proton mass difference in isospin-asymmetric nuclear matter U. -G. Meißner, A. M. Rakhimov, A. Wirzba and U. T. Yakhshiev Eur. Phys. J. A, 32 3 (2007) 299-309 Published online: 08 June 2007 DOI: 10.1140/epja/i2007-10390-9