The curvature of F-2(p) (x, Q(2)) as a probe of the range of validity of perturbative QCD evolutions in the small-x region

Perturbative NLO and NNLO QCD evolutions of parton distributions are studied, in particular in the (very) small-x region, where they are in very good agreement with all recent precision measurements of F-2(2)(x,Q(2)). These predictions turn out to be also rather insensitive to the specific choice of the factorization scheme (MS or DIS). A characteristic feature of perturbative QCD evolutions is a positive curvature of F p 2 which increases as x decreases. This perturbatively stable prediction provides a sensitive test of the range of validity of perturbative QCD.