216 research outputs found
Extension of worldline computational algorithms for QCD to open fermionic contours
The worldline casting of a gauge field system with spin-1/2 matter fields has
provided a, particle-based, first quantization formalism in the framework of
which the Bern-Kosower algorithms for efficient computations in QCD acquire a
simple interpretation. This paper extends the scope of applicability of the
worldline scheme so as to include open fermionic paths. Specific algorithms are
established which address themselves to the fermionic propagator and which are
directly applicable to any other process involving external fermionic states.
It is also demonstrated that in this framework the sole agent of dynamics
operating in the system is the Wilson line (loop) operator, which makes a
natural entrance in the worldline action; everything else is associated with
geometrical properties of particle propagation, of which the most important
component is Polyakov's spin factor.Comment: 24 page
Spin microscopy with enhanced Wilson lines in the TMD parton densities
We discuss the possibility of non-minimal gauge invariance of
transverse-momentum-dependent parton densities (TMDs) that allows direct access
to the spin degrees of freedom of fermion fields entering the operator
definition of (quark) TMDs. This is achieved via enhanced Wilson lines that are
supplied with the spin-dependent Pauli term , thus providing an appropriate tool for the "microscopic"
investigation of the spin and color structure of TMDs. We show that this
generalization leaves the leading-twist TMD properties unchanged but modifies
those of twist three by contributing to their anomalous dimensions. We also
comment on Collins' recent criticism of our approach.Comment: 4 pages. Presented at the XIV Workshop on High Energy Spin Physics,
20-24 Sept 2011, Dubna, Russi
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