Photon impact factor and $k_T$-factorization for DIS in the   next-to-leading order
  The photon impact factor for the BFKL pomeron is calculated in the next-to-leading order (NLO) approximation using the operator expansion in Wilson lines. The result is represented as a NLO $k_T$-factorization formula for the structure functions of small-$x$ deep inelastic scattering. 
Ian Balitsky and Giovanni A. Chirilli
hep-ph