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A. S. Kapoyannis

Publications and source records attributed to A. S. Kapoyannis.

At least 19 recordsLinked to original sources

Lévy-like flights and fractal geometry of finite point sets

We study Lévy-like and truncated Lévy-like flights with step probability distribution of the form $r^{-1+ν}$ for negative, positive, and zero $ν$, focusing on the appearance of fractal geometry characteristics in the generated point sets. Forming ensembles of such point sets with fixed multiplicity, we develop simulation techniques leading to the desired value of correlation dimension in a vast continuous interval of scales. In particular, we demonstrate the possibility to produce ensembles of data sets with a low number of points with the needed properties. Furthermore, we show that the positive $ν$ distributions, apart from a region near the upper scale limit, show fractal behaviour that extends to infinitesimally low scales. As an example, we apply our findings to producing simulations relevant to the search for critical fluctuations, related to QCD critical endpoint, in heavy-ion collision experiments.

cond-mat.stat-mech↗

Chiral QCD phase in equilibrium with Hadron Gas and the location of the critical point

We develop a description of the equation of state of QCD matter with restored chiral symmetry, which is in thermal and chemical equilibrium with the hadronic phase. The hadron gas is described with thermodynamically consistent volume corrections. The chiral phase is composed of a set of few quark condensates, each of which corresponds to a family of hadrons with specific quark content. On the boundary between the two phases we apply the requirement of conservation of particle numbers per family. We use lattice calculations for temperatures below the transition curve to determine hadronic volumes. We find that the pion system plays decisive role in the shift of the transition from higher order (crossover) to first order. For four volume models we calculate the location of the critical point as function of critical temperature $T_c$ at vanishing baryon density. Particularly, if we additionally impose the equality between the densities of quarks contained in mesons and baryons, we find a critical point residing in the interval of baryon chemical potential $μ_B \simeq$ 233-267 MeV and of temperature $T \simeq$ 153-158 MeV.

nucl-th↗

Correlation Integral vs. second order Factorial Moments and an efficient computational technique

We develop a mapping between the factorial moments of the second order $F_2$ and the correlation integral $C$. We formulate a fast computation technique for the evaluation of both, which is more efficient, compared to conventional methods, for data containing number of pairs per event which is lower than the estimation points. We find the effectiveness of the technique to be more prominent as the dimension of the embedding space increases. We are able to analyse large amount of data in short computation time and access very low scales in $C$ or extremely high partitions in $F_2$. The technique is an indispensable tool for detecting a very weak signal hidden in strong noise.

hep-ph↗

Particle states of Lattice QCD

We determine the degeneracy factor and the average particle mass of particles that produce the Lattice QCD pressure and specific entropy at zero baryon chemical potential. The number of states of the gluons and the quarks are found to converge above $T=$230 MeV to almost constant values, close to the number of states of an ideal Quark-Gluon Phase, while their assigned masses retain high values. The number of states and the average mass of a system containing quarks in interaction with gluons are found to decrease steeply with increase of temperature between $T \sim 150$ and 160 MeV, a region contained within the region of the chiral transition. The minimum value of the number of states within this temperature interval indicates that the states are of hadronic nature.

hep-ph↗

Viscosity of a net-baryon fluid near the QCD critical point

In the dynamics of the QCD critical point, the net-baryon fluid, linked to the slow component of the order parameter, relaxes to a 3d Ising system in equilibrium. An analytical study of shear and bulk viscosity, with constraints imposed by the dynamics of the critical net-baryon fluid, the universality property and the requirements of a class of strong coupling theories, is performed in the neighbourhood of the critical point. It is found that the shear viscosity of the net-baryon fluid is restricted in the domain $1.6\leq 4π\fracη{s}\leq 3.7$ for $T_c < T \leq 2T_c$ whereas the bulk viscosity is small, $4π\fracζ{s} < 0.05$ (for $T>1.27 T_c$) but rising towards the singularity at $T=T_c$.

nucl-th↗

Evidence for divergent baryon-number susceptibility in QCD matter

The baryon-number density formed in relativistic nuclear collisions, versus the chemical potential of the freeze-out states, is systematically studied on the basis of existing measurements. A remarkable power-law behaviour of the baryon-number susceptibility is found at the SPS, consistent with the existence of a QCD critical point at $μ_{B,c}\simeq 214$ MeV, $T_c\simeq 155$ MeV. The equation of state in different asymptotic regimes of the critical region is also examined and confronted with freeze-out states in these experiments.

hep-ph↗

Application of the Gibbs equilibrium conditions to the QGP-Hadron transition curve

A method is developed to consistently satisfy the Gibbs equilibrium conditions between the quark-gluon and hadronic phase, although each phase has been formulated in separate grand canonical partition functions containing three quark flavours. The sector in the space of thermodynamic variables, where the transition takes place, is restricted to a curve, according to the phase diagram of QCD. The conservation laws of quantum numbers are also imposed on the transition curve. The effect of the inclusion of the newly discovered pentaquark states is considered. The freeze-out conditions of S+S, S+Ag (SPS) and Au+Au (RHIC) are found compatible with a primordial QGP phase, but the conditions indicated by Pb+Pb (SPS) are not.

hep-ph↗

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↗

Critical Opalescence in Baryonic QCD Matter

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 behaviour 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.

hep-ph↗

The Critical Endpoint of Bootstrap and Lattice QCD Matter

The critical sector of strong interactions at high temperatures is explored in the frame of two complementary approaches: Statistical Bootstrap for the hadronic phase and Lattice QCD for the Quark-Gluon partition function. A region of thermodynamic instability of hadronic matter was found, as a direct prediction of Statistical Bootstrap. As a result, critical endpoint solutions for nonzero chemical potential were traced in the phase diagram of strongly interacting matter. These solutions are compared with recent lattice QCD results and their proximity to the freeze-out points of experiments with nuclei at high energies is also discussed.

hep-ph↗

Deriving the QGP-hadron transition curve from two separate partition functions

A method is developed to consistently satisfy the Gibbs equilibrium conditions between the quark-gluon and hadronic phase although each phase has been formulated in separate grand canonical partition function containing three quark flavours. The sector in the space of thermodynamic variables where the transition takes place is restricted to a curve, according to the phase diagram of QCD. The conservation laws of quantum numbers are also imposed on the transition curve. The effect of the inclusion of the newly discovered pentaquark states is considered. The freeze-out conditions of S+S, S+Ag (SPS) and Au+Au (RHIC) are found compatible with a primordial QGP phase, but the conditions indicated by Pb+Pb (SPS) are not.

hep-ph↗

Prospects of detecting the QCD critical point

We investigate the possibility to observe the QCD critical point in A+A collisions at the SPS. Guided by the QCD phase diagram expressed in experimentally accessible variables we suggest that the process C+C at 158 GeV/n freezes out very close to the critical point. We perform an analysis of the available preliminary experimental data for a variety of SPS processes. The basic tool in our efforts is the reconstruction of the critical isoscalar sector which is formed at the critical point. Our results strongly support our proposition regarding the C+C system.

hep-ph↗

Locating the QCD Critical Point in the Phase Diagram

It is shown that the hadronic matter formed at high temperatures, according to the prescription of the statistical bootstrap principle, develops a critical point at nonzero baryon chemical potential, associated with the end point of a first-order, quark-hadron phase-transition line. The location of the critical point is evaluated as a function of the MIT bag constant.

hep-ph↗

Quark-Hadron Critical Point consistent with Bootstrap and Lattice QCD

The critical sector of strong interactions at high temperatures is explored in the frame of two complementary paradigms: Statistical Bootstrap for the hadronic phase and Lattice QCD for the Quark-Gluon partition function. A region of thermodynamic instability of hadronic matter was found, as a direct prediction of Statistical Bootstrap. As a result, critical end point solutions for nonzero chemical potential were traced in the phase diagram of strongly interacting matter, consistently with chiral QCD and recent lattice calculations. The relevance of these solutions for current and future experiments with nuclei at high energies is also discussed.

hep-ph↗

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↗

Bootstraping the QCD Critical Point

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.

hep-ph↗

Conservation of particle multiplicities between chemical and thermal freeze-out

The evolution of a hadronic system after its chemical decomposition is described through a model that conserves the hadronic multiplicities to their values at chemical freeze-out. In the partition function describing the model all known hadronic resonances with masses up to 2400 MeV have been included. The state of the system is found as function of temperature and the corresponding baryon density is evaluated. The baryon density at thermal decoupling is also computed.

hep-ph↗

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↗