PHD, Kent State University, 2024, College of Arts and Sciences / Department of Physics

The thermodynamics of N = 4 supersymmetric Yang-Mills theory in four dimensions (SYM4,4) is of great interest since, at finite-temperature, the weak-coupling limit of this theory has many similarities with quantum chromodynamics (QCD). Unlike QCD, however, in SYM4,4 it is possible to make use of the AdS/CFT correspondence between gravity in anti-de Sitter space (AdS) and the large-Nc limit of conformal field theories (CFT) on the boundary of AdS to obtain results for SYM4,4 thermodynamics in the strong coupling limit. The mathematical structure of SYM4,4 is similar to that of QCD, the difference is mostly in the number of degrees of freedom and the representations of fields. There are four Majorana fermions and six scalars and all the fields are in the adjoint representation. In the last decade or so the thermodynamics of SYM4,4 in a strong-coupling regime received a great deal of attention due to AdS/CFT where in SYM4,4 is mapped to its gravity dual. In this limit, the thermodynamics has been computed to the order λ−3/2, where λ = Nc g2 is the ‘t Hooft coupling. In the opposite sector of weak coupling, prior to our work, the free energy density of SYM4,4 was known to the order λ3/2. In this regime, calculations are performed using perturbative field theory methods. This weak-coupling expansion of SYM4,4 like QCD can pushed until λ5/2, after which non-perturbative effects come into play. In this SYM4,4 free energy density expansion interesting observations are made by constructing a generalized Pade which interpolates between strong and weak coupling expansion. The weak coupling expansion converges towards this Pade for λ ≲ 1 and the strong coupling for λ ≳ 10. The makes the weak and strong coupling expansion and their convergence in the intermediate region of 1 ≲ λ ≲ 10 of a great deal of interest. On the weak-coupling side the free energy density calculations in SYM4,4, like in QCD, are done and improved upon using various perturbative field t (open full item for complete abstract)

Committee: Michael Strickland Dr. (Advisor); Zhangbu Xu Dr. (Committee Member); Artem Zvavitch Dr. (Committee Member); Edgar Koojiman Dr. (Committee Member); Khandker Quader Dr. (Committee Member) Subjects: Nuclear Physics; Particle Physics; Physics

PHD, Kent State University, 2021, College of Arts and Sciences / Department of Physics

The goal of high-energy nuclear physics is to understand the dynamics and properties of the various forms and phases of the strongly-interacting matter. Heavy-ion collision experiments are performed to deposit a large energy density in a very small volume of space and generate a form of extremely hot matter called the quark-gluon plasma (QGP). The behavior of the generated matter shows signatures of collectivity allowing phenomenological models based on statistical or fluid dynamical descriptions to be used successfully to analyze the outcomes the experiments. However, the very short lifetime and the extreme conditions of the QGP call for the construction of theoretical models based on the physics of nonequilibrium systems. Understanding the properties of QGP requires the study of collective excitations in the emergent many-body dynamics of the quarks and gluons as the fundamental objects in the theory of quantum chromodynamics. In this dissertation, the collective excitations of the nonequilibrium QGP are studied by calculating the quark and gluon self-energies within the hard loop effective theory. By extracting the solutions of the gluon dispersion relation in the complex plane, the presence of unstable modes in the momentum-anisotropic QGP is studied. The quark self-energy is also used to calculate the rate of photon emission from QGP in the subsequent studies performed as part of this dissertation. Electromagnetic probes (photons and dileptons) are considered among the best observables for extracting information about the early stages of evolution of the strongly interacting matter produced in heavy-ion collisions. In contrast to the hadrons, the emitted photons and leptons are not distorted by a strong coupling to the medium and they can escape the system with much larger mean free paths. Since the dilepton and photon emission rates from QGP are directly affected by the momentum distribution of the partonic degrees of freedom, their emission patter (open full item for complete abstract)

Committee: Michael Strickland Dr. (Advisor); Declan Keane Dr. (Committee Member); Jonathan Selinger Dr. (Committee Member); Barry Dunietz Dr. (Committee Member); Gang Yu Dr. (Committee Member) Subjects: Nuclear Physics; Particle Physics; Physics

Doctor of Philosophy, The Ohio State University, 2021, Physics

The study of heavy-ion collisions presents a challenge to both theoretical and experimental nuclear physics. Due to the extremely short (10^{-23} s) lifetime and small size (10^{-14} m) of the collision system, disentangling information provided by experimental observables, and progress in physical insight, requires the careful application of plausible reasoning. I apply a program of statistical methodologies, primarily Bayesian, to quantify properties of the medium in specific models, as well as compare and criticize differing models of the system. Of particular interest are estimations of the specific shear and bulk viscosities, where we find that information carried by the experimental data is still limited. In particular we find a large sensitivity to prior assumptions at high temperatures. Moreover, sensitivities to model assumptions are present at low temperatures, and this source of model uncertainty is propagated with model averaging and model mixing.

Committee: Ulrich Heinz (Advisor) Subjects: Nuclear Physics; Physics

Bachelor of Sciences, Ohio University, 2016, Physics and Astronomy

Over the past 15 years, we have seen much evidence of the existence of quark gluon plasma. This evidence was established through Au+Au and Pb+Pb collisions at the Relativistic Heavy Ion Collider (RHIC). In recent studies, it was confirmed that deuteron and gold nuclei collisions might also produce the quark gluon plasma, albeit in much smaller quantities. To further test this trend, helium-3 nuclei were collided with gold nuclei to study the quark gluon plasma signatures. In this study, p0 - h± azimuthal angular correlations and trigger yields in He+Au collisions are measured at 200 GeV and compared to d+Au collisions and p+p collisions at the same energy. To analyze the data we use IAA plots and RI (double ratio) plots, the latter being originally proposed by Bing Xia [1]. In d+Au and Au+Au collisions we see a suppression of the RI in high momentum regions and an enhancement of the RI in low momentum regions. The enhancement and suppression is a result of jet quenching due to the quark gluon plasma being created in both of these collisions. While the IAA plots for He+Au collisions conformed to the trend set by Au+Au and d+Au collisions, the RI plots deviated from the trend. Instead, we found suppression in low momentum regions and an enhancement in high momentum regions. In an effort to explain this deviation, detector modifications were checked and the effect of hydrodynamic flow was also checked. While there is a possibility that the geometry of helium-3 may have affected hydrodynamic flow, simulations implied that this is not the case. This result implies that these collisions should be looked into further.

Committee: Justin Frantz Dr. (Advisor) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2002, Physics

The nontrivial topological structure of the QCD gauge vacuum generates a CP breaking term in the QCD Lagrangian. However, measurements of the neutron electric dipole moment have demonstrated that the term's coefficient is unnaturally small, a dilemma known as the strong CP problem. A massless up quark has long been seen as a potential solution, as the term could then be absorbed through the resulting freedom to perform arbitrary chiral rotations on the up quark field. Through the light-quark-mass ratio mu/md, leading order Chiral Perturbation Theory appears to rule this scenario out. However, the Kaplan-Manohar ambiguity demonstrates that certain strong next-to-leading order corrections are indistinguishable from the effects of an up quark mass. Only a direct calculation of the Gasser-Leutwyler coefficient combination 2L8 - L5 can resolve the issue. New theoretical insights into partial quenched Chiral Perturbation Theory have revealed that a calculation of the low-energy constants of the partially quenched chiral Lagrangian is equivalent to a determination of the physical Gasser-Leutwyler coefficients. The coefficient combination in question is directly accessible through the pion mass's dependence on the valence quark mass, a dependence ripe for determination via Lattice Quantum Chromodynamics. We carry out such a partially quenched lattice calculation using Nf = 3 staggered fermions and the recently developed smearing technique known as hypercubic blocking. Through the use of several ensembles, we make a quantitative assessment of our systematic error. We find 2L8 - L5 = (0.22 ± 0.14 ) × 10-3, which corresponds to a light-quark-mass ratio of mu/md = 0.408 ± 0.035. Thus, our study rules out the massless-up-quark solution to the strong CP problem. This is the first calculation of its type to use a physical number of light quarks, Nf = 3, and the first determination of L8 - L5 to include a comprehensive study of statistical error.

Committee: Junko Shigemitsu (Advisor) Subjects: