How to impose initial conditions for QCD evolution of double parton   distributions?
  Double parton distribution functions (DPDFs) are used in the QCD description of double parton scattering. The DPDFs evolve with hard scales through QCD evolution equations which obey nontrivial momentum and valence quark number sum rules. We describe an attempt to construct initial conditions for the evolution equations which exactly fulfil these sum rules and discuss its shortcomings. We also discuss the factorization of the DPDFs into a product of two single parton distribution functions at small values of the parton momentum fractions. 
Krzysztof Golec-Biernat, Emilia Lewandowska
hep-ph