Soft and collinear gluon radiation and factorization in perturbation theory and beyond

by Einan GARDI (CERN - TH)

Friday 10 May 2002, 14:00 → 15:00 Europe/Zurich

TH Auditorium (CERN)

Power corrections to differential cross sections in the proximity of a kinematic threshold are analysed in the framework of Dressed Gluon Exponentiation. Exploiting the factorization property of soft and collinear radiation, a large class of radiative corrections which dominate the perturbative expansion in this region is resummed, yielding a renormalization-scale invariant expression for the Sudakov exponent. It is conjectured that factorization applies beyond the perturbative level. Thus information on power corrections can be drawn from the resummed perturbative calculation. The interplay between Sudakov logs and renormalons is clarified, and the necessity to resum the latter whenever power corrections are non-negligible is emphasized. Two examples are discussed. The first is event-shape distributions in the two-jet region, where there is no operator product expansion (OPE), and the second is deep inelastic (DIS) structure functions, where the OPE applies, but breaks down dramatically at large Bjorken x. In the DIS case, a detailed analysis of twist four is reported on, where it is shown precisely how the twist-two renormalon ambiguity eventually cancels out. This analysis provides a physical picture which substantiates the non-perturbative factorization conjecture.