Minimal subtraction vs. physical factorisation schemes in small-x QCD

We investigate the relationship of “physical” parton densities defined by k-factorisation, to those in the minimal subtraction scheme, by comparing their small-x behaviour. We first summarize recent results on the above scheme change derived from the BFKL equation at NLx level, and we then propose a simple extension to the renormalisation-group-improved (RGI) equation. In this way we are able the examine the difference between resummed gluon distributions in the Q0 and MS¯ schemes and also to show MS¯ scheme resummed results for Pgg and approximate ones for Pqg. We find that, due to the stability of the RGI approach, small-x resummation effects are not much affected by the scheme-change in the gluon channel, while they are relatively more important for the quark-gluon mixing.