Proton structure functions in the dipole picture of BFKL dynamics

The $F_2$, $F_G$, $R = F_L/F_T$ proton structure functions are derived in the QCD dipole picture. Assuming $k_T$ and renormalization-group factorization, we relate deep-inelastic proton scattering to deep-inelastic onium scattering. We get a three-parameter fit of the 1994 H1 data in the low-$x,$ moderate $Q^2$ range. The ratios $F_G/F_2$ and $R$ are predicted without further adjustment. The dipole picture of BFKL dynamics is shown to provide a relevant model for quantitatively describing the proton structure functions at HERA. The predictions for $F_2$ and $F_G$ are compatible with the next-to-leading order DGLAP analysis, while $R$ is expected to be significantly lower at very small $x$.