Harmonic expansion of the effective potential in Functional Renormalization Group at finite chemical potential

In this paper we propose a method to study the Functional Renormalization Group at finite chemical potential. The method consists of mapping the FRG equations within the Fermi surface into a differential equation defined on a rectangle with zero boundary conditions. To solve this equation we use an expansion of the potential in a harmonic basis. With this method we determined the phase diagram of a simple Yukawa-type model; as expected, the bosonic fluctuations decrease the strength of the transition.Comment: 15 pages, 10 figure

Heavy quarks or compactified extra dimensions in the core of hybrid stars

Neutron stars with extremely high central energy density are natural laboratories to investigate the appearance and the properties of compactified extra dimensions with small compactification radius, if they exist. Using the same formalism, these exotic hybrid stars can be described as neutron stars with quark core, where the high energy density allows the presence of heavy quarks (c, b, t). We compare the two scenarios for hybrid stars and display their characteristic features.Comment: Talk given at 4th International Workshop on New Worlds in Astroparticle Physics, Faro, Portugal, 5-7, Sep 2002. 10 pages, 6 EPS figure

Pion production in d+Au collisions at RHIC energy

We present our results on neutral pion pi0 production in pp and dAu collisions at RHIC energy. Pion spectra are calculated in a next-to-leading order (NLO) perturbative QCD-based model. The model includes the transverse component of the initial parton distribution (``intrinsic kT''). We compare our results to the available experimental data from RHIC, and fit the data with high precision. The calculation tuned this way is repeated for the dAu collision, and used to investigate the interplay of shadowing and multiple scattering at RHIC. The centrality dependence of the nuclear modification factor shows a measurable difference between different shadowing parameterizations.Comment: Final version published in the Eur. Phys. J. ST in the Proceedings of the Zimanyi Memorial Workshop, 2-4 July, 2007, Budapest, Hungary; 12 pages in Latex, 6 EPS figure

New Entropy Formula with Fluctuating Reservoir

Finite heat reservoir capacity and temperature fluctuations lead to modification of the well known canonical exponential weight factor. Requiring that the corrections least depend on the one-particle energy, we derive a deformed entropy, K(S). The resulting formula contains the Boltzmann-Gibbs, the Renyi and the Tsallis formulas as particular cases. For extreme large fluctuations (compared to the Gaussian case) a new, parameter-free entropy - probability relation emerges. This formula and the corresponding canonical equilibrium distribution are nearly Boltzmannian for high probability, but deviate from the classical result for low probability. In the extreme large fluctuation limit the canonical distribution resembles for low probability the cumulative Gompertz distribution

Jet Tomography Studies in AuAu Collision at RHIC Energies

Recent RHIC results on pion production in AuAu collision at sqrt(s)=130 and 200 AGeV display a strong suppression effect at high p_T. This suppression can be connected to final state effects, namely jet energy loss induced by the produced dense colored matter. Applying our pQCD-based parton model we perform a quantitative analysis of the measured suppression pattern and determine the opacity of the produced deconfined matter.Comment: Talk given at European Physical Society International Europhysics Conference on High Energy Physics HEP2003, July 17-23. 2003, in Aachen, Germany 3 pages in LaTeX, 2 EPS figure. (Accepted for publication in European Physical Journal C direct

Perturbative QCD Results on Pion Production in pp, pA and AA Collisions

We summarize new pQCD results on pion production in proton-proton (pp), proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our calculation introduces intrinsic parton transverse momentum (k_T) and is performed effectively at next-to-leading order (NLO), applying a K factor extracted for jet events. Two different factorization scales, Q=p_{T,jet}/2 and p_{T,jet} are used. Experimental data in pA collisions imply a preference for the latter choice at NLO level. We display our results at CERN SPS for AA collisions.Comment: Talk given at Budapest Workshop on Quark and Hadron Dynamics in Relativistic Heavy Ion Collisions (BP 2002) Budapest, Hungary, 3-7 Mar 2002. 11 pages in Latex, 7 PS figure. Submitted to Heavy Ion Physic

High-p_T Pion Production in Heavy-Ion Collisions at RHIC energies

Perturbative QCD results on pion production are presented in proton-proton, proton-nucleus and nucleus-nucleus collisions from CERN SPS up to RHIC energy. A K_{jet}(s, p_T, Q) factor obtained from jet production is applied to perform next-to-leading order calculations. Using the intrinsic transverse momentum (k_T) we determined transverse momentum spectra for pions in wide energy region. We have investigated nuclear multiscattering and the Cronin effect at RHIC energies.Comment: Talk given at XXXII. International Symposion on Multiparticle Dynamics (ISMD'02) Alusha, Crimea, Ukraine, 7-13 September 2002. 4 pages in Latex, 1 PS figur