The description of F-2 at very high parton densities

The behavior of the structure function at high energies (high densities) is directly associated to the gluon distribution. In this Letter we analyze t he asymptotic behavior of the structure function at very high densities con sidering a leading and a higher twist relation between these two quantities . We verify that (a) if the leading twist relation between the structure fu nction and the gluon distribution is used, we recover the black disc limit, and (b) a softer behavior is predicted if a higher twist relation between F-2 and xG is considered. While the first behavior is well-established by t he current high density approaches, the higher twist behavior is a new resu lt. In both cases, the F-2 structure function unitarizes and the Froissart boundary is not violated in the asymptotic regime of high density QCD. (C) 2001 Published by Elsevier Science B.V.