Browsing by Author "Peshier, Andre"

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    Bose-Einstein condensation from a gluon transport equation
    (2018) Harrison, Brent; Peshier, Andre
    In this thesis we investigate the evolution of the quark gluon plasma, as produced in the early stages of a relativistic heavy ion collision, towards equilibrium. To this end we put forward a new numerical scheme to solve the QCD Boltzmann equation in the small-scattering angle approximation, which we develop here for the quenched limit of QCD. We initially restrict our analysis to spatially homogeneous systems of gluons distributed isotropically in momentum space. With our scheme we confirm results of Blaizot et al. [1], in particular that for certain “overpopulated” initial conditions, a transient Bose-Einstein condensate emerges during equilibriation in a finite time. We further analyse the dynamics of the formation of this condensate. We then extend our scheme to systems with cylindrically symmetric momentum distributions, in order to investigate the effects of anisotropy. In particular we compare the rates at which isotropization and equilibriation occur. We also compare our results from the small-scattering angle scheme to the relaxation-time approximation.
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    Finite size effects in the thermodynamics of the free scalar field and the interacting SU(3) plasma
    (2018) Mohamed, Husam; Peshier, Andre
    In this thesis, we study the thermodynamic properties of the free scalar field and the thermodynamics of the interacting SU(3) plasma when these systems are away from the thermodynamic limit, i.e., at finite volume. In the first part of the thesis, we study the thermodynamic properties of the free scalar field in a variety of finite-size geometries (the cube, the cuboid and the parallel-plates geometries) when the field is subjected to Dirichlet and periodic boundary conditions; we also give a brief review of the thermodynamic properties of the free scalar field on discretized Euclidian space-time lattices. In the second part of the thesis, we discuss briefly the thermodynamic properties of the quark-gluon plasma in the continuum and thermodynamic limits, and then we use a quasi-particle model of the SU(3) plasma to shed some light on the interplay of finite-size and generic interaction effects in the context of lattice QCD calculations.
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    Full 3+1 dimensional simulation of the relativistic Boltzmann equation
    (2021) Grunow, Ernst William; Peshier, Andre
    Relativistic hydrodynamics has been the tool of choice to simulate the dynamics of the quark-gluon plasma produced in heavy-ion collisions. Despite the success of hydrodynamics, it has several shortcomings stemming from the fact that it assumes a system close to equilibrium. An alternative to hydrodynamics is solving the Boltzmann equation, which describes the evolution of the full distribution function of the system without the close to equilibrium requirement. Large scale simulations using the Boltzmann equation, however, has hitherto proved computationally intractable due to their computational expense. By using a novel algorithm, and leveraging the computational power of graphical processor units, we numerically integrate the Boltzmann equation in the relaxation time approximation.
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    J / ( ) production in heavy ion collisions at the STAR detector at RHIC
    (2012) Powell, Christopher Beresford; Cleymans, Jean; Peshier, Andre
    The success of the Standard Model of particle physics in describing a large variety of experimental results has been supported by the prediction and subsequent discovery of the charm, bottom, and top quarks, and the Z, W±, and Higgs bosons. The theory of Quantum Chromodynamics (QCD), which describes the strong interaction between quarks and gluons in the Standard Model, predicts a phase transition from hadronic matter to a deconfined Quark Gluon Plasma (QGP) at high temperature and energy density. The Relativistic Heavy Ion Collider (RHIC) was built to achieve these conditions to test the predictions of QCD and understand the properties of a deconfined medium. Charm (c) quarks have been suggested as ideal probes of the medium created in heavy ion collisions, as they are created primarily in the initial hard scattering of the collision because of their large mass.
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    PHY1004W - Matter & Interactions
    (2014-09-18) Buffler, Andy; Fearick, Roger; Govender, Indresan; Peshier, Andre
    PHY1004W is a first-year, calculus-based introductory Physics course for Science students intending to continue with second-year Physics. MODERN MECHANICS: Matter and interactions, conservation laws, the momentum principle, atomic nature of matter, conservation of energy, energy in macroscopic systems, energy quantization, multiparticle systems, exploring the nucleus, angular momentum, entropy, kinetic theory of gases, efficiency of engines. ELECTRIC AND MAGNETIC INTERACTIONS: Electric fields, electric potential, magnetic fields, electric circuits, capacitance, resistance, magnetic force, Gauss' law, Ampere's law, Faraday's law, induction, electromagnetic radiation, waves and particles, semiconductor devices.
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    QCD Boltzmann equation: beyond the soft-scattering approximation
    (2022) Moodley, Nicole; Peshier, Andre
    In this thesis we use the case study of a spatially homogeneous many-gluon system, distributed isotropically in momentum space, to study the evolution of a hot (quark-) gluon plasma from an initial state towards equilibrium. To that end, we investigate the QCD Boltzmann equation making use of a calculation scheme that reproduces the known result for scalar interactions and generalizes to a QCD interaction, under an approximation of soft scattering.
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    The Runny Gauge Plasma: shear viscosity to entropy for quarks and gluons
    (2016) Jackson, Greg; Peshier, Andre
    Heavy ion experiments at the LHC and RHIC have supported the existence of a quark-gluon plasma (QGP), which is strongly coupled and behaves as an almost ideal fluid. We shall discuss both bulk thermodynamic and off-equilibrium transport properties of the QGP, within the theory of quantum chromodynamics (QCD). Meaningful approximations of most observables require quantum fluctuations to be taken into account. These arise in perturbation theory as loop corrections to tree level amplitudes, and describe both the scale-dependence of the coupling and charge screening in a many- body system. We emphasise that because the effective interaction strength, for a QGP, may vary considerably at the relevant scales, the running of the coupling cannot be ignored. The goal of this thesis is to understand better a specific, long-standing question in the field of heavy ion physics: why the QGP has a remarkably small shear viscosity to entropy density ratio η/s ~< 0:5, near the confinement temperature. Our main argument hinges on combining both the thermal and vacuum fluctuations in resummation-improved perturbation theory. In this respect, we thoroughly analyse the range of applicability for perturbative approximations in which the coupling may be 'moderately' large.η