N. Antoniou

Bootstraping the QCD critical point

Abstract It is shown that hadronic matter formed at high temperatures, according to the prescription of the statistical bootstrap principle, develops a critical point at nonzero baryon chemical potential. The location of the critical point in the phase diagram, however, depends on the detailed knowledge of the partition function of the deconfined phase, near the critical line. In a simplified version of the quark–gluon partition function, the resulting location of the critical point is compared with the solutions of other approaches and in particular with the results of lattice QCD. The proximity of our solution to the freeze-out area in heavy-ion experiments is also discussed.

Fractal geometry of critical systems

We investigate the geometry of a critical system undergoing a second-order thermal phase transition. Using a local description for the dynamics characterizing the system at the critical point T=T(c), we reveal the formation of clusters with fractal geometry, where the term cluster is used to describe regions with a nonvanishing value of the order parameter. We show that, treating the cluster as an open subsystem of the entire system, new instanton-like configurations dominate the statistical mechanics of the cluster. We study the dependence of the resulting fractal dimension on the embedding dimension and the scaling properties (isothermal critical exponent) of the system. Taking into account the finite-size effects, we are able to calculate the size of the critical cluster in terms of the total size of the system, the critical temperature, and the effective coupling of the long wavelength interaction at the critical point. We also show that the size of the cluster has to be identified with the correlation length at criticality. Finally, within the framework of the mean field approximation, we extend our local considerations to obtain a global description of the system.

FRACTALS AT T = TC DUE TO INSTANTONLIKE CONFIGURATIONS

We investigate the geometry of the critical fluctuations for a general system undergoing a thermal second order phase transition. Adopting a generalized effective action for the local description of the fluctuations of the order parameter at the critical point (

Critical opalescence in baryonic QCD matter.

T=T_c

A new SPS programme

) we show that instanton-like configurations, corresponding to the minima of the effective action functional, build up clusters with fractal geometry characterizing locally the critical fluctuations. The connection between the corresponding (local) fractal dimension and the critical exponents is derived. Possible extension of the local geometry of the system to a global picture is also discussed.

Critical events and intermittency in nuclear collisions

We show that critical opalescence, a clear signature of second-order phase transition in conventional matter, manifests itself as critical intermittency in QCD matter produced in experiments with nuclei. This behavior is revealed in transverse momentum spectra as a pattern of power laws in factorial moments, to all orders, associated with baryon production. This phenomenon together with a similar effect in the isoscalar sector of pions (sigma mode) provide us with a set of observables associated with the search for the QCD critical point in experiments with nuclei at high energies.

Criticality, fractality, and intermittency in strong interactions.

A new experiemntal program to study hadron production in hadron-nucleus and nucleus-nucleus collisions at the CERN SPS has been recently proposed by the NA49-future collaboration. The physics goals of the program are: -Search for the critical point of strongly interacting matter and a study of the properties of the onset of deconfinemnt in nucleus-nucleus collisions, -Measurements of correlations, fluctuations and hadron spectra at high pT in proton-nucleus collisions needed as for better understanding of nucleus-nucleus results, -Measurements of hadron production in hadron-nucleus interactions needed for neutrino (T2K) and cosmic-ray (Pierre Auger Observatory and KASCADE) expriments. The physics of the nucleus-nucleus program is reviewed in this presentation.

Fractality in rapidity space and low temperature intermittency in multihadron processes

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.

Indication of divergent baryon-number susceptibility in QCD matter

Assuming a second-order phase transition for the hadronization process, we attempt to associate intermittency patterns in high-energy hadronic collisions to fractal structures in configuration space and corresponding intermittency indices to the isothermal critical exponent at the transition temperature. In this approach, the most general multidimensional intermittency pattern, associated to a second-order phase transition of the strongly interacting system, is determined, and its relevance to present and future experiments is discussed.

Evolutionary intermittency and the QCD critical point

We study intermittency effects in high energy collisions introducing a fractal measure in rapidity space and formulationg the hadronization sector of the S-matrix within the Ginzburg-Landau approach. The properties of the critical Feynman-Wilson fluid provide us with a boundary condition forT=Tc whereas a low temperatures (T≪Tc) a strong amplification of the intermittency effect is found, corresponding to a local minimum of the effective free energy. The significance of this solution for the interpretation of the intermittency phenomenon for low multiplicities is discussed and a comparison with experimental measurements is attempted, within the two-component model.