Non-Markovian source term for particle production by a self-interacting scalar field in the large-N approximation

The particle production in the self-interacting N-component complex scalar field theory is studied at large N. A non-Markovian source term that includes all higher order back-reaction and collision effects is derived. The kinetic amplitudes accounting for the change in the particle number density caused by collisions are obtained. It is shown that the production of particles is symmetric in the momentum space. The problem of renormalization is briefly discussed.Comment: minor changes, journal versio

Net Baryon Fluctuations from a Crossover Equation of State

We have constructed an equation of state which smoothly interpolates between an excluded volume hadron resonance gas at low energy density to a plasma of quarks and gluons at high energy density. This crossover equation of state agrees very well with lattice calculations at both zero and nonzero baryon chemical potential. We use it to compute the variance, skewness, and kurtosis of fluctuations of baryon number, and compare to measurements of proton number fluctuations in central Au-Au collisions as measured by the STAR collaboration in a beam energy scan at the Relativistic Heavy Ion Collider. The crossover equation of state can reproduce the data if the fluctuations are frozen out at temperatures well below than the average chemical freeze-out.Comment: 5 pages, 7 figures. arXiv admin note: substantial text overlap with arXiv:1506.0340

Matching Excluded Volume Hadron Resonance Gas Models and Perturbative QCD to Lattice Calculations

We match three hadronic equations of state at low energy densities to a perturbatively computed equation of state of quarks and gluons at high energy densities. One of them includes all known hadrons treated as point particles, which approximates attractive interactions among hadrons. The other two include, in addition, repulsive interactions in the form of excluded volumes occupied by the hadrons. A switching function is employed to make the crossover transition from one phase to another without introducing a thermodynamic phase transition. A chi-square fit to accurate lattice calculations with temperature $100 < T < 1000$ MeV determines the parameters. These parameters quantify the behavior of the QCD running gauge coupling and the hard core radius of protons and neutrons, which turns out to be $0.62 \pm 0.04$ fm. The most physically reasonable models include the excluded volume effect. Not only do they include the effects of attractive and repulsive interactions among hadrons, but they also achieve better agreement with lattice QCD calculations of the equation of state. The equations of state constructed in this paper do not result in a phase transition, at least not for the temperatures and baryon chemical potentials investigated. It remains to be seen how well these equations of state will represent experimental data on high energy heavy ion collisions when implemented in hydrodynamic simulations.Comment: 19 pages, 9 figure

Modification of Z Boson Properties in Quark-Gluon Plasma

We calculate the change in the effective mass and width of a Z boson in the environment of a quark-gluon plasma under the conditions expected in Pb-Pb collisions at the LHC. The change in width is predicted to be only about 1 MeV at a temperature of 1 GeV, compared to the natural width of 2490$\pm$7 MeV. The mass shift is even smaller. Hence no observable effects are to be expected.Comment: 7 pages latex file with 6 embedded PS figure

Thermal Conductivity and Chiral Critical Point in Heavy Ion Collisions

Background: Quantum Chromodynamics is expected to have a phase transition in the same static universality class as the 3D Ising model and the liquid-gas phase transition. The properties of the equation of state, the transport coefficients, and especially the location of the critical point are under intense theoretical investigation. Some experiments are underway, and many more are planned, at high energy heavy ion accelerators. Purpose: Develop a model of the thermal conductivity, which diverges at the critical point, and use it to study the impact of hydrodynamic fluctuations on observables in high energy heavy ion collisions. Methods: We apply mode coupling theory, together with a previously developed model of the free energy that incorporates the critical exponents and amplitudes, to construct a model of the thermal conductivity in the vicinity of the critical point. The effect of the thermal conductivity on correlation functions in heavy ion collisions is studied in a boost invariant hydrodynamic model via fluctuations, or noise. Results: We find that the closer a thermodynamic trajectory comes to the critical point the greater is the magnitude of the fluctuations in thermodynamic variables and in the 2-particle correlation functions in momentum space. Conclusions: It may be possible to discern the existence of a critical point, its location, and thermodynamic and transport properties near to it in heavy ion collisions using the methods developed here.Comment: 36 pages, 8 figures. Version published in Phys.Rev.C86, 054911 (2012). It contains some minor improvements with respect to v1: further clarifications, small changes on figures and two extra reference