Does a massive vector field imply spontaneous symmetry breaking?

Working in the classical tree approximation and for the Abelian case only we indicate the existence of converse routes to the Higgs mechanism. In particular, we show how a carefully formulated compatibility between gauge invariance and massiveness of a vector field leads to spontaneous breakdown of the local symmetry.     

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

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.     

Chiral QCD phase transition in nuclear collisions

The characteristic aspects of multiparticle states generated at , as a result of chiral QCD phase transition, are studied in the framework of the O(4) theory. Predictions concerning critical events, in connection with current and future experiments with ultrarelativistic heavy ions, are presented. Received: 9 June 1997 / Revised version: 18 July 1997 / Published online: 26 February 1998     

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

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. Received: 22 December 1999 / Published online: 6 April 2000     

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

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 ( pair annihilation) cross-sections. We emphasize that this is the first time that world-line techniques are applied to cross-section calculations. Received: 10 June 2002 / Published online: 31 October 2002 RID="a" ID="a" e-mail: akaranik@cc.uoa.gr RID="b" ID="b" e-mail: cktorid@cc.uoa.gr RID="c" ID="c" e-mail: stefanis@tp2.ruhr-uni-bochum.de     

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 nonperturbative confining effects, as contained in the stochastic vacuum model of H. Dosch and Yu.A. Simonov, are considered in the context of a (hypothetical) quark-quark “scattering process” in the Regge kinematical region. In a computation wherein the nonperturbative input enters as a correction to established perturbative results, a careful treatment of infrared divergences 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 a contribution from a tachyonic ghost state, an occurrence which is fully consistent with earlier suggestions made in the context of low-energy QCD phenomenology.     

A special construction of Berezin'sL-Kernel

We consider Berezin's algebraic considerations regarding the quantization of phase space polynomials. After making a connection with Prugoveki's stochastic quantization approach, we give a particular construction of Berezin's L-Kernel in terms of Prugoveki's -functions.     

A space–time approach to multi-gluon loop 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.