Chromomagnetism, flavour symmetry breaking and S-wave tetraquarks F. Buccella, H. Høgaasen, J.-M. Richard and P. Sorba Eur. Phys. J. C, 49 3 (2007) 743-754 Published online: 18 November 2006 DOI: 10.1140/epjc/s10052-006-0142-1