Low-energy pions in nuclear matter and ππ photoproduction within a BUU transport model O. Buss, L. Alvarez-Ruso, P. Mühlich and U. Mosel Eur. Phys. J. A, 29 2 (2006) 189-207 Published online: 28 August 2006 DOI: 10.1140/epja/i2006-10075-y