Markus Diehl

Time ordering in off-diagonal parton distributions

We investigate the relevance of time ordering in the definition of off-diagonal parton distributions in terms of products of fields. The method we use easily allows determination of their support properties and provides a link to their interpretation from a parton point of view. It can also readily be applied to meson distribution amplitudes.

Exclusive electroproduction of vector mesons and transversity distributions

We show that the leading twist contribution to exclusive electroproduction of transversely polarized vector mesons vanishes at all orders in perturbation theory. Therefore one cannot extract information on the quark transversity distribution of the nucleon from this reaction. In turn one has that the produced vector meson is purely longitudinal in the large-Q^2 limit, which provides a new test of the dominance of leading twist at finite Q^2.

Unintegrated parton density functions

An overview on activities to determine unintegrated parton density functions is given and the concept and need for unintegrated PDFs is discussed. It is also argued that it is important to reformulate perturbative QCD results in terms of fully unintegrated parton densities, differential in all components of the parton momentum. Also the need for non-linear BFKL evolution is discussed and results using the BK equation supplemented by DGLAP corrections at shortndistances is reviewed. Finally the use unintegrated generalized parton distributions for hard diffractive processes is discussed.