C.N. Ktorides

The Delta nucleon transition form-factors in chiral perturbation theory

The three complex form factors entering the ∆ → Nγ∗ vertex are calculated to O(ε3) in the framework of a chiral effective theory with explicit ∆(1232) degrees of freedom included. Corrections to leading contributions entering the expansion in inverse powers of the chiral symmetry breaking scale Λχ are identified. It is shown that the low q 2 behavior of the form factors is governed by πN , π∆ loop effects. Furthermore, the role of presently unknown low energy constants that affect the values of the transition-multipole ratios EMR and CMR is elucidated. PACS numbers: Typeset using REVTEX ∗e-mail: ggellas@atlas.cc.uoa.gr †email: th.hemmert@fz-juelich.de ‡e-mail: gpoulis@rtm.iasa.uoa.gr 1

Worldline approach to Sudakov-type form factors in non-Abelian gauge theories

We calculate Sudakov-type form factors for isolated spin-12 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.

World-line techniques for resumming gluon radiative corrections at the cross-section level

Abstract. We employ the Polyakov world-line path-integral version of QCD to identify and resum at leading perturbative order enhanced radiative gluon contributions to the Drell-Yan type (

Probing the boundaries of the hadronic phase through a strangeness- including statistical bootstrap model

q\bar{q}

Spinorial charges and their role in the fusion of internal and space-time symmetries

pair annihilation) cross-sections. We emphasize that this is the first time that world-line techniques are applied to cross-section calculations.

Zig zag symmetry in AdS/CFT duality

A recently constructed strangeness-including Statistical Bootstrap Model (S-SBM), which defines the limits of the hadronic phase and provides for a phase beyond, is further extended so as to include a factor that describes strangeness suppression. The model is then used to analyse the multiplicity data from collision experiments in which the colliding entities form isospin symmetric systems, the primary focus being on S+S interactions (NA35 collaboration). An optimal set of thermodynamical variables is extracted through a fit to both the inclusive full phase space and midrapidity data. The assumption that the measured particles originate from a thermally and partial-chemically equilibrated source described by the S-SBM is satisfactorily established. The proximity of the thermodynamical variables extracted from the S+S data to the limits of the hadronic phase is systematically investigated. Finally, experimental data from proton-antiproton collisions (UA5 collaboration) are similarly analysed.

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

Abstract The advent of supersymmetry immediately led to speculations that a non-trivial mixing of internal and space-time symmetries could be achieved within its framework. In fact, the well-known no-go theorems do not apply to the supersymmetry algebra due to the presence, in the latter, of (anticommuting) spinorial charges. However, not until the recent work of Haag, Lopuszanski and Sohnius did a clearcut picture emerge as to how the aforementioned nontrivial mixing can take place. Most notably, the presence of the conformal algebra within the supersymmetry algebra turns out to be vital. We solidify the findings of Haag et al. through an explicit construction which uses as underlying space the pseudo-Euclidean space E(4,2), i.e. the space for which the conformal group is the group of rotations, and which employs as main tools the spinors associated with the space E(4,2). We follow the algebro-geometric approach of Cartan in order to understand both the introduction and the properties of these spinors. In this manner, we gain many insights regarding the mathematical foundations of supersymmetry. Thus, we fully understand the emergence of the anticommutator, rather than the commutator, among spinor charges as a natural algebraic consequence and not as an a priori given fact. In addition, we clearly see how an (internal) unitary symmetry group can make its appearance within the supersymmetry scheme and verify, via our explicit construction, the results of Haag et al.

Critical events and intermittency in nuclear collisions

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 ’t Hooft 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.

Perturbative computation of the gluonic effective action via Polyakov’s world-line path integral

Abstract. A generalized strangeness-including statistical bootstrap model (SSBM) is constructed so as to include independent 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 of the source being outside the hadronic domain.

Worldline approach to forward and fixed angle fermion-fermion scattering in Yang-Mills theories at high energies

Abstract The structure of events in relativistic heavy ion collisions (RHIC), associated with chiral QCD phase transition, is investigated. In particular the density fluctuations of pions, emitted from the excited vacuum (at T ≈ T c ), are studied and classified in terms of intermittency patterns in rapidity space. For this purpose a Monte Carlo simulation of critical events in the central region is presented, on the basis of the O (4) theory of chiral phase transition. The universal character of these events is revealed and the predictions of the theory are discussed in connection with event by event measurements in current and future experiments with relativistic heavy ions.