Author: Nopoush Mohammad
Publisher:
Published: 2019
Total Pages: 0
ISBN-13:
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Relativistic heavy-ion collision experiments are currently the only controlled way to generate and study matter in the most extreme temperatures (T ~10e+12 K). At these temperatures matter undergoes a phase transition to an exotic phase of matter called the quark-gluon plasma (QGP). The QGP is an extremely hot and deconfined phase of matter where sub-nucleonic constituents (quarks and gluons) are asymptotically free. The QGP phase is important for different reasons. First of all, our universe existed in this phase up to approximately t ~10e-5 s after the Big Bang, before it cools down sufficiently to form any kind of quark bound states. In this regard, studying the QGP provides us with useful information about the dynamics and evolution of the early universe. Secondly, high-energy collisions serve as a microscope with a resolution on the order of 10e-15 m (several orders of magnitude more powerful than the best ever developed electron microscopes). With this fantastic probe, penetrating into the detailed structure of nucleons, and the discovery of new particles and fundamental phases are made possible. The dynamics of the QGP is based on quantum chromodynamics (which governs the interactions of quarks and gluons) and the associated force is "strong force". The strong collective behaviors observed experimentally inspired people to use dissipative fluid dynamics to model the dynamics of the medium. The QGP produced in heavy-ion collisions, experiences strong longitudinal expansion at early times which leads to a large momentum-space anisotropy in the local rest frame distribution function. The rapid longitudinal expansion casts doubt on the application of standard viscous hydrodynamics (vHydro) models, which lead to unphysical predictions such as negative pressure, negative one-particle distribution function, and so on. Anisotropic hydrodynamics (aHydro) takes into account the strong momentum-space anisotropy in the leading order distribution function in a consistent and systematic way. My dissertation is about the formulation and application of anisotropic hydrodynamics as a successful non-equilibrium hydrodynamics model for studying the QGP. For this purpose, I introduce the basic conformal anisotropic hydrodynamics formalism and then explain the ways we included realistic features (bulk degree of freedom, quasiparticle implementation of realistic equation of state, more realistic collisional kernel), to make it a suitable hydrodynamics model for studying the QGP generated in heavy-ion collisions. For verification of our model we have compared the evolution of model parameters predicted by aHydro and vHydro, with exact analytical solution of the Boltzmann equation. For this purpose, we have studied the evolution of the system under conformal Gubser flow using the aHydro model. By transforming to de Sitter spacetime (a non-trivial curved coordinate system) we simplified the dynamics to 0+1d spacetime. Comparisons with exact solutions show that aHydro better reproduces the exact solutions than the best available vHydro models. However, the system is not conformal and the aHydro needed to be improved to include a realistic prescription for the equation of state which takes care of non-ideal effect in the dynamics. In the framework of finite temperature eld theory the equation of state is provided by numerical calculation of QCD partition function using lattice QCD (LQCD), whereas, devising an equation of state for aHydro model is challenging because therein we deal with anisotropic pressures. In the next step of my research, we have designed a novel method for implementing the realistic equation of state (provided by lattice QCD) in the aHydro formalism. This model, called the quasiparticle aHydro model, integrates the non-conformal effects in the aHydro model. The non-conformal effects are due to strong interactions of plasma constituents which leads to temperature-dependence of the particles' effective mass in the system. Based on the quasiparticle picture, we have developed the quasiparticle aHydro (aHydroQP) model which has all necessary components for studying the phenomenology of the QGP created in heavy-ion collisions. We have then compared the phenomenological predictions of the aHydroQP model with experimental observations. Comparisons illustrate a high level of consistency between our model and the experimental data. The last two chapters are about two applications of the aHydro model to field-theoretical measurables in the QGP. In these chapters, we have calculated the quark self-energy in an anisotropic QGP. The quark self-energy is important because it encodes the way quarks gain interactional mass while in the hot QGP. I also have presented the calculation of gluon self-energy in hard loop approximation in an anisotropic QGP.The gluon self-energy is important since it is related to heavy-quark potential and heavy quarkonium suppression. Heavy quarkonia bound states, besides theoretical importance, serve as a thermometer for the QGP.
