Alternatives to DGLAP in the theory of the Deep-Inelastic Scattering
Prof. Boris Ermolaev
(Ioffe Physico-Technical Institute, Russia)
Sala P7, IST, Edifício Matemática
Tuesday, November 4th, 2008 at 04:00 PM
The most popular theoretical instrument for describing
the Deep-Inelastic Scattering (DIS) is Standard Approach (SA). It is
applied to description of all DIS structre function. SA combines the
DGLAP evolution equations and standard fits for the initial parton
densities. In spite of the fact that DGLAP was originally
suggested for describing DIS at large x and large Q^2, it is rather
successfully applied to experiment beyond this region at small x, though
without theoretical grounds.
The small-x alternative to SA for the unpolarizec DIS involves the BFKL
equation. The presently available experimental data cannot discriminate
between those approaches
We present an alternative approach to the Polarized DIS. It accounts for
the total resummation of the leading logs of x and Q^2. Contrary to
DGLAP, the value of Q^2 in our approach should not be kept large.
We re-examine the well-known DGLAP parametrization of alpha_s and find it
to be true at large x and large starting point of the Q^2 -evolution
only, otherwise it should be changed.
We show that efficience of SA at small x is entirely based on using
special fits for the initial parton densities which mimic the total
resummation of ln(x). When the resummation is taken into account, the
fits can be seriously simplified.
We demonstrate that using SA beyond the proper DGLAP applicability region
(large x and large Q^2) leads to various misconceptions and discuss them.
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