Applications of the leading-order Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations to the combined HERA data on deep inelastic scattering

We recently derived explicit solutions of the leading-order Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equations for the $Q^2$ evolution of the singlet structure function $F_s(x,Q^2)$ and the gluon distribution $G(x,Q^2)$ using very efficient Laplace transform techniques. We apply our results here to a study of the HERA data on deep inelastic $ep$ scattering as recently combined by the H1 and ZEUS groups. We use initial distributions $F_2^{\gamma p}(x,Q_0^2)$ and $G(x,Q_0^2)$ fixed by a global fit to the HERA data. From $F_2^{\gamma p}(x,Q_0^2)$ we obtain the singlet quark distribution $F_s(x,Q_0^2)$---using small non-singlet quark distributions taken from either the CTEQ6L or the MSTW2008LO analyses---evolve to arbitrary $Q^2$, and then convert the results to individual quark distributions. Finally, we show directly from a study of systematic trends in a comparison of the evolved $F_2^{\gamma p}(x,Q^2)$ with the HERA data, that the assumption of leading-order DGLAP evolution is inconsistent with those data.