63,681 research outputs found
On scale dependence of QCD string operators
We have obtained a general solution of evolution equations for QCD twist-2
string operators in form of expansion over complete set of orthogonal
eigenfunctions of evolution kernels in coordinate-space representation. In the
leading logarithmic approximation the eigenfunctions can be determined using
constraints imposed by conformal symmetry. Explicit formulae for the LO
scale-dependence of quark and gluon twist-2 string operators are given
Chiral-Odd and Spin-Dependent Quark Fragmentation Functions and their Applications
We define a number of quark fragmentation functions for spin-0, -1/2 and -1
hadrons, and classify them according to their twist, spin and chirality. As an
example of their applications, we use them to analyze semi-inclusive
deep-inelastic scattering on a transversely polarized nucleon.Comment: 19 pages in Plain TeX, MIT CTP #221
Disentangling Intertwined Embedded States and Spin Effects in Light-Front Quantization
Naive light-front quantization, carried out by a light-front energy
integration of covariant amplitudes, is not guaranteed to generate the
corresponding Feynman amplitudes. In an explicit example we show that the
nonvalence contribution to the minus-component of the EM current of a meson
with fermion constituents has a persistent end-point singularity. Only after
this term is subtracted, the result is covariant and satisfies current
conservation. If the spin-1/2 constituents are replaced by spin zero ones, the
singularity does not occur and the result is, without any adjustment, identical
to the Feynman amplitude. Numerical estimates of valence and nonvalence
contributions are presented for the cases of fermion and boson constituents.Comment: 17 pages and 9 figure
- …