25 research outputs found
Geometry of gauge links in operator definitions of transverse-momentum dependent PDFs: A comparative view
Different approaches to the problem of a gauge-invariant operator definition
of transverse-momentum dependent parton densities (TMDs) are reviewed and
compared from the point of view of their compatibility with the operator
definition of collinear (integrated) parton distribution functions. In
particular, geometry of the longitudinal and transverse gauge links (Wilson
lines) both in unsubtracted quark TMDs and in the associate soft factors is
addressed. A possible connection between different operator definitions is also
discussed.Comment: 9 pages, 4 figures. Presented at the International Conference
"Photon-2011", 22-27 May 2011 Spa, Belgiu
TMD PDF's: gauge invariance, RG properties and Wilson lines
The UV divergences associated with transverse-momentum dependent (TMD) parton
distribution functions (PDF) are calculated together with the ensuing one-loop
anomalous dimensions in the light-cone gauge. Time-reversal-odd effects in the
anomalous dimensions are observed and the role of Glauber gluons is discussed.
A generalized renormalization procedure of TMD PDFs is proposed, relying upon
the renormalization of contour-dependent operators with obstructions.Comment: 4 pages, 1 figure. Talk presented at the International Workshop on
Diffraction in High Energy and Nuclear Physics, La Londe-les-Maures, France,
9-14 Sept 2008. v2: 5 pages, preprint number and e-mail addresses adde
Calculation of Ground State Energy for Confined Fermion Fields
A method for renormalization of the Casimir energy of confined fermion fields
in (1+1)D is proposed. It is based on the extraction of singularities which
appear as poles at the point of physical value of the regularization parameter,
and subsequent compensation of them by means of redefinition of the "bare"
constants. A finite ground state energy of the two-phase hybrid model of
fermion bag with chiral boson-fermion interaction is calculated as the function
of the bag's size.Comment: 10 pages, LaTeX; no figures. Version to appear in Phys. Lett. B
(2001
Instanton Contribution to the Quark Form Factor
The nonperturbative effects in the quark form factor are considered in the
Wilson loop formalism. The properties of the Wilson loops with cusp
singularities are studied taking into account the perturbative and
nonperturbative contributions, where the latter are considered within the
framework of the instanton liquid model. For the integration path corresponding
to this form factor -- the angle with infinite sides -- the explicit expression
for the vacuum expectation value of the Wilson operator is found to leading
order. The calculations are performed in the weak-field limit for the instanton
vacuum contribution and compared with the one- and two-loop order results for
the perturbative part. It is shown that the instantons produce the powerlike
corrections to the perturbative result, which are comparable in magnitude with
the perturbative part at the scale of order of the inverse average instanton
size. It is demonstrated that the instanton contributions to the quark form
factor are exponentiated to high orders in the small instanton density
parameter.Comment: Version coincident with the journal publication. LaTeX, 15 pages, 1
figur
Nonperturbative contributions to the quark form factor at high energy
The analysis of nonperturbative effects in high energy asymptotics of the
electomagnetic quark form factor is presented. It is shown that the
nonperturbative effects determine the initial value for the perturbative
evolution of the quark form factor and find their general structure with
respect to the high energy asymptotics. Within the Wilson integral formalism
which is natural for investigation of the soft, IR sensitive, part of the
factorized form factor, the structure of the instanton induced effects in the
evolution equation is discussed. It is demonstrated that the instanton
contributions result in the finite renormalization of the subleading
perturbative result and numerically are characterized by small factor
reflecting the diluteness of the QCD vacuum within the instanton liquid model.
The relevance of the IR renormalon induced effects in high energy asymptotic
behaviour is discussed. The consequences of the various analytization
procedures of the strong coupling constant in the IR domain are considered.Comment: REVTeX, 12 pages, 1 figure. Important references and discussions
added, misprints corrected, minor changes in tex