Small-x parton content of the photon.

Abstract

The parton content of the photon is examined systematically. In the low-${Q}^{2}$ region (${Q}^{2}<1$ ${\mathrm{GeV}}^{2}$) we assume the photon behaves largely according to the vector-meson-dominance (VMD) hypothesis, while for higher ${Q}^{2}$ we supplement the VMD with a purely perturbative pointlike component and QCD corrections. Special care is taken in the region of small $x$: we work in the leading-logarithm approximation (LLA) in $\frac{1}{x}$ at low ${Q}^{2}$ and in the LLA in ${Q}^{2}$ for ${Q}^{2}>4$ ${\mathrm{GeV}}^{2}$. We include small-$x$ shadowing effects in the VMD sector and show that they need not be considered in the pointlike sector where the parton content is much less.