Searcharxiv⌕ Search

arXiv subjects

C. N. Ktorides

Publications and source records attributed to C. N. Ktorides.

At least 19 recordsLinked to original sources
arXiv2009

Worldline Casting of the Stochastic Vacuum Model and Non-Perturbative Properties of QCD: General Formalism and Applications

The Stochastic Vacuum Model for QCD, proposed by Dosch and Simonov, is fused with a Worldline casting of the underlying theory, i.e. QCD. Important, non-perturbative features of the model are studied. In particular, contributions associated with the spin-field interaction are calculated and both the validity of the loop equations and of the Bianchi identity are explicitly demonstrated. As an application, a simulated meson-meson scattering problem is studied in the Regge kinematical regime. The process is modeled in terms of the "helicoidal" Wilson contour along the lines introduced by Janik and Peschanski in a related study based on a AdS/CFT-type approach. Working strictly in the framework of the Stochastic Vacuum Model and in a semiclassical approximation scheme the Regge behavior for the Scattering amplitude is demonstrated. Going beyond this approximation, the contribution resulting from boundary fluctuation of the Wilson loop contour is also estimated.

hep-ph↗
arXiv2008

Non-Perturbative Regge Exchange in Meson-Meson Scattering: An Analysis Based on the Stochastic Vacuum Model

Employing the Worldline casting of the Dosch-Simonov Stochastic Vacuum Model(SVM) for QCD, a simulated meson-meson scattering is studied in the Regge kinematical regime. The process is modelled in terms of the "helicoidal" Wilson contour first introduced by Janic and Peschanski in a related study based on an AdS/CFT-type approach. Using lattice supported estimations for the behavior of a two-point, field strength correlation function, as defined in the framework of the SVM, the reggeon slope and intercept are calculated in a semiclassical approximation. The resulting values are in good agreement with the accepted phenomenological ones. Going beyond this approximation, the contribution resulting from boundary fluctuations of the Wilson loop contour is also estimated.

hep-ph↗
arXiv2007

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.

hep-th↗
arXiv2007

Establishing the Uniqueness of the Connection between SdS_5 and Conformally Invariant Relativistic Systems: A Group/Field Theoretical Approach

Adopting as working assumption that the conformal group O(4,2) of Minkowski space, being the largest symmetry group which respects its light cone structure, is the appropriate global symmetry underlying the description of relativistic systems, it is shown that AdS$_5$ uniquely emerges as the space on the boundary of which a corresponding relativistic field system should be accommodated. The basic mathematical tools employed for establishing this result are (a) Cartan's theory of spinors and (b) group contraction methods. Extending our considerations to supersymmetry it is demostrated how an $N$=1 SUSY YM field system can emerge as a broken version of an $N$=4 SUSY YM field system. An especially important feature of the presentation is the `unearthing' of seminal, independent from each other, works of I. Segal and of S. Fubini which give a purely field theoretical perspective on the intimate relation between conformally invariant relativistic field theories and AdS$_5$ including, in particular, the warping phenomenon.

hep-th↗
arXiv2006

An Alternative for Moduli Stabilisation

The one-loop vacuum energy is explicitly computed for a class of perturbative string vacua where supersymmetry is spontaneously broken by a T-duality invariant asymmetric Scherk-Schwarz deformation. The low-lying spectrum is tachyon-free for any value of the compactification radii and thus no Hagedorn-like phase-transition takes place. Indeed, the induced effective potential is free of divergence, and has a global anti de Sitter minimum where geometric moduli are naturally stabilised.

hep-th↗
arXiv2006

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.

hep-th↗
arXiv2004

Non-perturbative corrections to perturbative results pertaining to a four-point Sudakov process in QCD

Within the framework of the Fock-Feynman-Schwinger (equivalently, worldline) casting of QCD a four-point process, mediated by a closed quark loop, is studied in the Sudakov kinematical region, first perturbatively and subsequently with the inclusion of non-perturbative contributions through the use of the stochastic vacuum model. Deformations of the, first order, perturbative results are determined. Finally, the resummation of the leading logarithmic terms is performed and physical implications of the result are discussed.

hep-ph↗
arXiv2004

Theoretical evidence for a tachyonic ghost state contribution to the gluon propagator in high energy, forward quark-quark `scattering'

Implications stemming from the inclusion of non-perturbative, confinining effects, as contained in the Stochastic Vacuum Model of Dosch and Simonov, are considered in the context of a, hypothetical, quark-quark `scattering process' in the Regge kinematical region. In a computation wherein the non-perturbative input enters as a correction to established perturbative results, a careful treatment of infrared divergencies is shown to imply the presence of an effective propagator associated with the existence of a linear term in the static potential. An equivalent statement is to say that the modified gluonic propagator receives contribution from a tachyonic ghost state, an occurence which is fully consistent with earlier such suggestions made in the context of low energy QCD phenomenology.

hep-ph↗
arXiv2004

A numerical algorithm for computing the complete set of one-gluon loop diagrams in QCD on the basis of a single master expression

A numerical program is presented which facilitates the computation of 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 number of which increases with M. An important component of the numerical program is an algorithm for computing multi-Grassmann variable integrals. The cases M=2, 3, 4, which are the only ones having divergent terms, are fully worked out. A complete agreement with known, analytic results pertaining to the divergent terms is attained.

hep-th↗
arXiv2002

A global assessment of the Strangeness including-Statistical Bootstrap Model analysis of nucleus-nucleus and proton-antiproton interactions

A strangeness and isospin asymmetry including statistical bootstrap model analysis of the multiparticle system produced in the Pb+Pb collision at 158 AGeV at CERN is presented. It is concluded that this interaction process has not crossed the deconfinenent line. Direct comparisons with the results of similar analyses pertaining to nucleus-nucleus and proton-antiproton collisions at CERN are made. The overall picture points to the S+S collision at 200 AGeV as a prime candidate of a process which has crossed the border separating the hadronic from the deconfined phase of matter.

hep-ph↗
arXiv2002

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.

hep-th↗
arXiv2002

Resummation of perturbatively enhanced gluon radiative corrections

By remaining strictly within the confines of QCD, i.e., {\it without} invoking the parton model or any other exogenous element, we identify and resum perturbatively to leading order, along with a correction term, enhanced radiative gluon contributions to the Drell-Yan type ($q\bar{q}$ pair annihilation) and deep-inelastic-scattering type ($eq\to eq+X$) cross-sections. The key feature of the adopted approach is the recasting of QCD in terms of a space-time mode of description, which employs a path-integral formulation of field theories, as originally implied in works of Fock, Feynman and Schwinger.

hep-ph↗
arXiv2000

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.

hep-ph↗
arXiv2000

Polyakov's spin factor and new algorithms for efficient perturbative computations in QCD

Polyakov's spin factor enters as a weight in the path-integral description of particle-like modes propagating in Euclidean space-times, accounting for particle spin. The Fock-Feynman-Schwinger path integral applied to QCD accomodates Polyakov's spin factor in a natural manner while, at the same time, it identifies Wilson line (loop) operators as sole agents of interaction dynamics among matter and gauge field quanta. A direct application of such a separation between spin content and dynamics is the emergence of master expressions for the perturbative series involving either open or closed fermionic lines which provide new, comprehensive approaches to perturbative QCD.

hep-th↗
arXiv1999

Statistical Bootstrap analysis of S+Ag interaction at 200AGeV: Evidence of a phase beyond the hadronic one?

A generalized Strangeness-incorporating Statistical Bootstrap Model (SSBM) is constructed so as to include indepedent fugacities for up and down quarks. Such an extension is crucial for the confrontation of multiparticle data emerging from heavy ion collisions, wherein isospin symmetry is not satisfied. Two constraints, in addition to the presence of a critical surface which sets the boundaries of the hadronic world, enter the extended model. An analysis pertaining to produced particle multiplicities and ratios is performed for the S+Ag interaction at 200 GeV/nucleon. The resulting evaluation, concerning the location of the source of the produced system, is slightly in favor the source being outside the hadronic domain.

hep-ph↗
arXiv1999

Off-mass-shell Sudakov-like suppression factor for the fermionic four-point function in QCD

We consider a four-point process, associated with a wide-angle elastic scattering of two off-mass-shell spin-1/2 matter particles, in a non-abelian gauge theory. On the basis of a worldline approach, which reverts the functional to a path-integral description of the system, we factorize an eikonal (``soft'') subsector of the full theory and calculate the Sudakov-like suppression factor for the four-point function as a whole, once we have extracted the associated anomalous dimensions and taken into account the renormalization-group controlled evolution.

hep-ph↗