41 research outputs found
A space-time approach to multigluon computations in QCD: An application to effective action terms
The applicability of the space-time formulation of the gluonic sector of QCD
in terms of the Polyakov worldline path integral, via the use of the background
field gauge fixing method, is extended to multi-gluon loop configurations.
Relevant master formulas are derived for the computation of effective action
terms.Comment: 10 page
Perturbative Computation of the Gluonic Effective Action via Polyaokov's World-Line Path Integral
The Polyakov world-line path integral describing the propagation of gluon
field quanta is constructed by employing the background gauge fixing method and
is subsequently applied to analytically compute the divergent terms of the one
(gluonic) loop effective action to fourth order in perturbation theory. The
merits of the proposed approach is that, to a given order, it reduces to
performing two integrations, one over a set of Grassmann and one over a set of
Feynman-type parameters through which one manages to accomodate all Feynman
diagrams entering the computation at once.Comment: 21 page
A numerical algorithm for efficiently obtaining a Feynman parameter representation of one-gluon loop QCD Feynman diagrams for a large number of external gluons
A numerical program is presented which facilitates a computation pertaining
to the full set of one-gluon loop diagrams (including ghost loop
contributions), with M attached external gluon lines in all possible ways. The
feasibility of such a task rests on a suitably defined master formula, which is
expressed in terms of a set of Grassmann and a set of Feynman parameters. The
program carries out the Grassmann integration and performs the Lorentz trace on
the involved functions, expressing the result as a compact sum of parametric
integrals. The computation is based on tracing the structure of the final
result, thus avoiding all intermediate unnecessary calculations and directly
writing the output. Similar terms entering the final result are grouped
together. The running time of the program demonstrates its effectiveness,
especially for large M.Comment: 32 pages, 5 figures. in press Computer Physics Communication
Non-perturbative quenched propagator beyond the infrared approximation
A new approach to the quenched propagator in QED beyond the IR limit is
proposed. The method is based on evolution equations in the proper time.Comment: 13 pages, 1 figure; Misprint on reference correcte
Zig Zag symmetry in AdS/CFT duality
The validity of the Bianchi identity, which is intimately connected with the
zig zag symmetry, is established, for piecewise continuous contours, in the
context of Polakov's gauge field-string connection in the large 'tHooft
coupling limit, according to which the chromoelectric `string' propagates in
five dimensions with its ends attached on a Wilson loop in four dimensions. An
explicit check in the wavy line approximation is presented.Comment: 24 pages version to appear in EPJ
Worldline approach to Sudakov-type form factors in non-Abelian gauge theories
We calculate Sudakov-type form factors for isolated spin-1/2 particles
(fermions) entering non-Abelian gauge-field systems. We consider both the on-
and the off-mass-shell case using a methodology which rests on a worldline
casting of field theories. The simplicity and utility of our approach derives
from the fact that we are in a position to make, a priori, a more transparent
separation (factorization), with respect to a given scale, between short- and
long-distance physics than diagramatic methods.Comment: 18 pages. RevTex is used. No figure
Analyticity and power corrections in hard-scattering hadronic functions
Demanding the analyticity of hadronic observables (calculated in terms of
power series of the running coupling) as a {\it whole}, we show that they are
free of the Landau singularity. Employing resummation and dispersion-relation
techniques, we compute in a unifying way power corrections to two different
hard-scattering functions in perturbative QCD: the electromagnetic pion form
factor to leading order and the inclusive cross section of the Drell-Yan
process. In the second case, the leading nonperturbative power correction in
gives rise to a Sudakov-like exponential factor in the
impact parameter space which provides enhancement rather than suppression.Comment: V1: 11 pages in RevTeX; 1 figure as EPS file; V2: typos in Eqs. (5)
and (24) corrected; V3: Phys. Lett. B. 504 (2001) 225; V4: The following
equations have been corrected: (2), (5), (14), (15), (21), (22), (27), (32),
(33), (34); one equation added: new (28). Figure corrected. Conclusions
unchange
Pion production from a critical QCD phase
A theoretical scheme which relates multiparticle states generated in
ultrarelativistic nuclear collisions to a QCD phase transition is considered in
the framework of the universality class provided by the 3-D Ising model. Two
different evolution scenarios for the QGP system are examined. The statistical
mechanics of the critical state is accounted for in terms of (critical) cluster
formation consistent with suitably cast effective action functionals, one for
each considered type of expansion. Fractal properties associated with these
clusters, characterizing the density fluctuations near the QCD critical point,
are determined. Monte-Carlo simulations are employed to generate events,
pertaining to the total system, which correspond to signals associated with
unconventional sources of pion production
Two different quasiparticle scattering rates in vortex line liquid phase of layered d-wave superconductors
We carry out a quantum mechanical analysis of the behavior of nodal
quasiparticles in the vortex line liquid phase of planar d-wave
superconductors. Applying a novel path integral technique we calculate a number
of experimentally relevant observables and demonstrate that in the low-field
regime the quasiparticle scattering rates deduced from photoemission and
thermal transport data can be markedly different from that extracted from
tunneling, specific heat, superfluid stiffness or spin-lattice relaxation time.Comment: Latex, 4 pages, no figure
Power corrections to the transition form factor and pion distribution amplitudes
Employing the standard hard-scattering approach and the running coupling
method we calculate a class of power-suppressed corrections to the electromagnetic transition form
factor (FF) arising from the end-point
integration regions. In the investigations we use a hard-scattering amplitude
of the subprocess , symmetrized under
exchange important for exclusive
processes containing two external photons. In the computations the pion model
distribution amplitudes (DA's) with one and two non-asymptotic terms are
employed. The obtained predictions are compared with the CLEO data and
constraints on the DA parameters and at the
normalization point are extracted. Further restrictions on
the pion DA's are deduced from the experimental data on the electromagnetic FF
.Comment: 23 pages, 6 figures; the version published in Phys. Rev. D69, 094010
(2004