Analytical calculations of four-neutrino oscillations in matter Y. Kamo, Y. Higasida, J.-I. Ichihara, S.-I. Kubota, S. Tokuo and S. Yajima Eur. Phys. J. C, 28 2 (2003) 211-221 Published online: 14 March 2003 DOI: 10.1140/epjc/s2003-01138-0