The contribution of off-shell gluons to the longitudinal structure function FL A.V. Kotikov, A.V. Lipatov and N.P. Zotov Eur. Phys. J. C, 27 2 (2003) 219-228 Published online: 24 January 2003 DOI: 10.1140/epjc/s2002-01107-1