Analytic expression for the joint x and Q2 dependences of the deep-inelastic structure functions

We obtain a good analytic fit to the joint Bjorken-x and Q2 dependences of ZEUS data on the deep-inelastic structure function F(2)(p)(x,Q2). At fixed virtuality Q2, as we showed previously, our expression is an expansion in powers of ln(1/x) that satisfies the Froissart bound. Here we show that for each x, the Q2 dependence of the data is well described by an expansion in powers of lnQ2. The resulting analytic expression allows us to predict the logarithmic derivatives (partial differential(n)F(2)(p)/(partial differentiallnQ2)n)x for n=1,2 and to compare the results successfully with other data. We extrapolate the proton structure function F(2)(p)(x,Q2) to the very large Q2 and the very small x regions that are inaccessible to present-day experiments and contrast our expectations with those of conventional global fits of parton distribution functions.