Update of MRST Parton Distributions

Abstract

I present a brief summary of the most important updates in the MRST determinations of the NLO and NNLO parton distributions. I concentrate on uncertainties due to input assumptions and possible theoretical corrections, particularly isospin violation, QED corrections, NNLO and corrections at low Q^2 and small x.

To appear in proceedings of "DIS 2004: XII International Workshop on Deep Inelatic Scattering" (Strbske Pleso, Slovakia, April 2004). 6 pages, 3 figures