410 research outputs found
Soft and hard pomerons
Regge theory provides an excellent description of small-
structure-function data from up to the highest available values. The
large- data should also be described by perturbative QCD: the two
descriptions must agree in the region where they overlap. However, at present
there is a serious lack in our understanding of how to apply perturbative QCD
at small . The usual lowest-order or next-to-lowest order expansion is not
valid, at least not until becomes much larger than is usually assumed; a
resummation is necessary, but as yet we do not know how to do this resummation.Comment: 8 pages, plain tex, with 6 figures embedded using epsf. Lecture at
Workshop on New Trends in HERA Physics, Ringberg (june 1999
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