Thesis advisor: Gabor Kalman / Complex plasma systems have been studied for a long time. In this thesis we focus on a quasi-2D layer system. In fact, most experimental studies of complex plasmas are based on 2D systems, because it is easy to use camera to record the in-plane movement of particles. Unfortunately, due to the finite confining strength, the system is not a strictly 2D layer, it is a quasi-2D layer. We firstly studied the density profile of such a quasi-2D system by density functional theory(DFT). From the density profile research result, we found that the system can form a trilayer structure with proper parameters. Then we studied the dynamical properties of a trilayer system, and for simplicity, we only studied an ideal three layer model, both in liquid and lattice case. In lattice case, we firstly searched the stable lattice structure at different inter-layer distance. Then we used lattice sites summation to construct the dynamical matrix and solve the dispersion relation. For liquid case, we did the theoretical prediction for the collective dispersion by quasi localized charge approximation(QLCA), then we extracted the collective mode information from the molecular dynamics(MD) simulation. The QLCA and MD results were compared and discussed. The reason for the previous gap discrepancy problem is discovered. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Ultracold neutral plasmas (UNP) are laboratory plasmas formed by the photoionization of a magneto-optically trapped and cooled gas. Because of their unusually low temperatures, UNPs are an example of a strongly coupled plasma, meaning that the potential energy of Coulomb interactions between particles is comparable to or greater than their thermal kinetic energy. In the field of strongly coupled plasmas, which also includes dense plasmas found in astrophysics and inertial confinement fusion experiments, there is a pressing need to better understand the collisional transport of matter, momentum, and energy between electrons and ions. The main result of this thesis is to demonstrate the existence of a new physical effect that significantly influences the electron-ion collision rates of strongly coupled plasmas. The essence of the effect is that the electron-ion collision rate depends explicitly on the sign of the colliding charges. This runs counter to both traditional plasma kinetic theory and modern extensions to strong coupling, all of which predict collision rates that do not depend on the sign of the electron-ion interaction. The effect is similar to a phenomenon observed charged-particle stopping known as the Barkas effect. The existence of the Barkas effect in the electron-ion collision rate of strongly coupled plasmas is first demonstrated using molecular dynamics (MD) simulations. A non-equilibrium simulation methodology is developed to extract the electron-ion collision frequency from the relaxation of an induced electron drift velocity. The simulations are carefully designed to ensure that the relaxation process can be modeled with a constant relaxation rate, which facilitates comparison with theoretical predictions developed later in the thesis. The Barkas effect becomes apparent when these simulations are repeated with positrons in place of electrons. It is seen that the positron-ion collision rate is always lower than the equivalent electron-ion one, and that this charge-sign asymmetry widens rapidly with increasing electron (or positron) coupling strength. It is hypothesized that the observed Barkas effect can be explained by accounting for plasma screening in the kinematics of binary electron-ion collisions. This is the main tenet of Effective Potential Theory (EPT), which assumes transport occurs through binary collisions governed by the potential of mean force. In order to apply EPT to electron-ion transport in UNPs, several new theoretical developments are made. First, it is demonstrated that EPT is able to accurately predict near-equilibrium transport in ionic mixtures as compared with equilibrium MD simulations. Next, a previously proposed model for the potentials of mean force in two-temperature positron-ion plasma is validated using a new two-thermostat MD methodology. Finally, EPT is applied to electron-ion transport in UNPs using a semi-analytic mapping between a two-component plasma and a screened one-component plasma system, which alleviates numerical difficulties in the theory associated with attractive interactions. The EPT predictions for the electron-ion and positron-ion relaxation rates are in excellent agreement with the MD simulations over the range of coupling strengths attained in present-day UNP experiments. EPT is thus shown to be the first transport theory for strongly coupled plasmas that accounts for the close-interaction physics that give rise to the Barkas effect in electron-ion transport.

A strongly-coupled plasma is a collection of free charged particles that interact with a Coulomb repulsion that is so strong that nearby particles do not easily move past one another. Unlike weakly-coupled plasmas, strongly-coupled plasmas exhibit a self-organization of particles into an arrangement like a solid crystalline lattice or a liquid. Dusty plasmas consist of micron-size particles of solid matter that are immersed in a plasma of electrons and ions. The dust particles gain a large electric charge and become strongly coupled. The motion of discrete particles can be tracked using a video microscopy diagnostic. Dusty plasma experiments allow a study of strongly-coupled plasma physics and an experimental simulation of condensed matter physics. Experiments are reported using a single layer of particles in the plasma to study two-dimensional (2D) physics. It is demonstrated experimentally that in addition to the solid and liquid states, a strongly-coupled dusty plasma can exist in an exotic state called a superheated solid. A 2D dusty plasma, initially self-organized in a crystalline lattice, is heated rapidly by rastered laser beams. The suspension remains in a solid lattice at a temperature well above the melting point. Shear-induced melting is studied in a 2D dusty plasma by applying shear to a crystalline lattice using a pair of oppositely-directed laser beams. Unexpectedly, coherent longitudinal waves are also excited in the resulting shear flow. In the first experiment of its kind, a suddenly-applied shear is found to produce a melting front that spreads at the transverse sound speed. The viscoelasticity of strongly-coupled plasmas in a liquid state is quantified. In the first experiment for any kind of physical system, the wavenumber-dependent viscosity, η(k), is computed from measurements of the random motion of particles. It is found that η(k) diminishes with increasing k, indicating that viscous behavior is gradually replaced by elastic behavior as the scale length is reduced. As a tool for studying transport at a microscopic level, the self-intermediate scattering function (self-ISF) is used in numerical simulations of 2D dusty plasmas. Two physical processes are studied using the self-ISF: relaxation of random motion, and melting. The wavenumber-dependence of the relaxation time in a liquid-phase strongly-coupled plasma is shown to be useful for distinguishing normal and anomalous diffusion. The self-ISF is also demonstrated to be a sensitive indicator of the melting transition. An improved image-analysis method is developed for calculating particle positions with minimal measurement errors. This development also provides an understanding of sources of error and the dependence on parameters that the experimenter can control.

The AdS/CFT correspondence and its extensions to more general gauge/gravity dualities have provided a powerful framework for the study of strongly coupled gauge theories. This thesis explores properties of a large class of thermal strongly coupled gauge theories using the gravity dual. In order to bring the holographic framework closer to Quantum Chromodynamics (QCD), we study theories with matter in the fundamental representation. In particular, we focus on the holographic dual of SU(Nc) supersymmetric Yang-Mills theory coupled to Nf<<Nc flavours of fundamental matter at finite temperature, which is realised as Nf Dq-brane probes in the near horizon (black hole) geometry of Nc black Dp-branes. We explore many aspects of these Dp/Dq brane systems, often focussing on the D3/D7 brane system which is dual to a four dimensional gauge theory. We study the thermodynamics of the Dq-brane probes in the black hole geometry. At low temperature, the branes sit outside the black hole and the meson spectrum is discrete and possesses a mass gap. As the temperature increases, the branes approach a critical solution. Eventually, they fall into the horizon and a phase transition occurs. At large Nc and large 't Hooft coupling, we show that this phase transition is always first order. We calculate the free energy, entropy and energy densities, as well as the speed of sound in these systems. We compute the meson spectrum for brane embeddings outside the horizon and find that tachyonic modes appear where this phase is expected to be unstable from thermodynamic considerations. We study the system at non-zero baryon density nb and find that there is a line of phase transitions for small nb, terminating at a critical point with finite nb. We demonstrate that, to leading order in Nf/Nc, the viscosity to entropy density ratio in these theories saturates the conjectured universal bound. Finally, we compute spectral functions and diffusion constants for fundamental matter in the high temperature phase of the D3/D7 theory.

A written report of a paper titled Holographic dual of collimated radiation by Veronika E. Hubeny where a new and easier method is proposed to estimate the “radiation due to an accelerated quark in a strongly coupled medium”. The method is able to reproduce the results from an earlier paper without the need of solving the linearized Einstein equations but by way of calculating geodesics in AdS using the AdS/CFT correspondence and the gravitational dual of the quark being a string. A quick introduction to synchrotron radiation and general relativity is given after which the AdS/CFT correspondence is introduced along with the results and method of V. Hubeny. / A bachelor thesis in theoretical physics.

The AdS/CFT correspondence and its extensions to more general gauge/gravity dualities have provided a powerful framework for the study of strongly coupled gauge theories. This thesis explores properties of a large class of thermal strongly coupled gauge theories using the gravity dual. In order to bring the holographic framework closer to Quantum Chromodynamics (QCD), we study theories with matter in the fundamental representation. In particular, we focus on the holographic dual of SU(Nc) supersymmetric Yang-Mills theory coupled to Nf<<Nc flavours of fundamental matter at finite temperature, which is realised as Nf Dq-brane probes in the near horizon (black hole) geometry of Nc black Dp-branes. We explore many aspects of these Dp/Dq brane systems, often focussing on the D3/D7 brane system which is dual to a four dimensional gauge theory. We study the thermodynamics of the Dq-brane probes in the black hole geometry. At low temperature, the branes sit outside the black hole and the meson spectrum is discrete and possesses a mass gap. As the temperature increases, the branes approach a critical solution. Eventually, they fall into the horizon and a phase transition occurs. At large Nc and large 't Hooft coupling, we show that this phase transition is always first order. We calculate the free energy, entropy and energy densities, as well as the speed of sound in these systems. We compute the meson spectrum for brane embeddings outside the horizon and find that tachyonic modes appear where this phase is expected to be unstable from thermodynamic considerations. We study the system at non-zero baryon density nb and find that there is a line of phase transitions for small nb, terminating at a critical point with finite nb. We demonstrate that, to leading order in Nf/Nc, the viscosity to entropy density ratio in these theories saturates the conjectured universal bound. Finally, we compute spectral functions and diffusion constants for fundamental matter in the high temperature phase of the D3/D7 theory.

Thesis advisor: Gabor J. Kalman / Mixtures of charged particles, where the components have different charge numbers (Z_A ), masses (m_A ) and densities (n_A ), with A = 1, 2 denoting the components, occur in Nature in a great variety. To be sure, even the simplest plasmas are necessarily multicomponent systems, consisting of negative and positive charges. This feature is, however, obscured within the centrally important and popular OCP (one component plasma) or jellium models, where the role of one of the components is reduced to providing a neutralizing background. When this background is inert, one is led to the Coulomb OCP model, while when the background is polarizable (such as an electron gas surrounding heavy particles), to a Yukawa OCP (YOCP), with a screened Yukawa potential replacing the Coulomb potential between the dynamically active particles. There are, however situations of physical importance, where the OCP description is inadequate and a genuine two component description of a plasma composed of two species is required. This Thesis focuses on the study of the dynamics of many-body systems consisting of two components of like charges (all the Z_A -s being of the same signature) in a neutralizing background. The methodology is based upon parallel attacks through theoretical analysis and Molecular Dynamics (MD) simulations, the latter yielding the capability of instant verification of the former. The investigation involves the study of the partial (i.e. species by species) structure functions S_AB (k, ω) and current-current correlation functions L_AB (k, ω). The Fluctuation–Dissipation Theorem (FDT) con- nects these quantities to the total and partial response functions χ_AB (k, ω) (matrices in species space), which are instrumental in the description of the collective mode excitations of the system. This analysis has revealed an entirely novel feature: both S_11 (k, ω) and S_22 (k, ω) exhibit very sharp and deep (several orders of magnitude) minima in the strongly coupled liquid phase at robust characteristic frequencies of the system, which are virtually coupling independent. The FDT then demands that these anti-resonances show up as well in the imaginary part of the partial density response function χ_AB (k, ω). Our theoretical analysis, based on the Quasi-Localized Charge Approximation (QLCA), has confirmed that this is indeed the case. These anti-resonant frequencies being related to the dissipative part of the response, require a physical description of the principal source of dissipation. This has been identified as the inter-species momentum transfer, governed by drag between the microscopic current fluctuations of the two species. The description of this effect was incorporatedv in the QLCA formalism, making it possible to derive a closed analytic representation of the fluctuation spectra in the frequency domain of interest and compare them with the results of the MD simulations. Other important novel concepts, such as the idea of coupling dependent effective mass, fast vs. slow sound, the mechanism of tran- sition from short-range to long-range interaction have been identified and analyzed. Furthermore, the investigation of the dynamics has led to the first comprehensive description of the mode structures of classical binary Coulomb and Yukawa mixtures at arbitrary coupling values, which has been a longstanding problem in statistical plasma physics. Focusing on the longitudinal excitations, we describe the transition from weak coupling (where one is acquainted with the RPA result yielding only the single plasmon mode in the Coulomb case or a single acoustic mode in the Yukawa case) to strong coupling, with a doublet of modes that arise from the complex rel- ative motion between the two components, as affected by the interaction with the background. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

No description available.

The local structures of the iron atoms for a series of strongly coupled Fe 2 (TIED)L 4 complexes (TIED = tetraiminethylenedimacrocycle, L = axail ligand) have been investigated by K-edge X-ray Absorption Spectroscopy (XAS). These complexes include not only the well characterized iso-valence CH 3 CN complex, mixed-valence CH 3 CN and Cl − complexes, and previously reported iso-valence CO complex but also the new isolated solids of iso-valence Fe 2 TIED complexes with Cl − , Br − , imidazole, pyridine, histidine, N,N-dimethyformamide (DMF), SCN − , and CN − as axial ligands and mixed-valence complexes with Br − and imidazole as axial ligands. The average Fe-N distances for the first coordination sphere of the iron atom obtained by EXAFS analysis are 1.94, 1.94, 1.95, 1.96, 1.94, 1.93, 1.96, 1.96, 1.96, and 1.96 Å for the iso- and mixed-valence CH 3 CN and imidazole complexes and iso-valence complexes with SCN − , CN − , CO, pyridine, histidine, and DMF as axial ligands, respectively. Two-shell fitting analyses of the complexes gave average iron to the four planar coordinated nitrogen distance of 1.90, 1.91, 1.91, 1.92, and 1.92 Å for the Fe 2 (TIED)L 4 with L = DMF, pyridine, Cl − , Br − , imidazole, and histidine complexes, respectively. The average distances from the center iron to: N(DMF), 2.05; N(pyridine), 2.05; Cl − , 2.33; Br − , 2.45; N(imidazole), 2.08; and N(histidine), 2.07 Å. They are all comparable to related bond distances in the literature. The above data indicate that there is no significant difference in the average Fe-N distances between each of the iso- and mixed-valence pairs. Also different axial ligands do not cause significant impact on the average Fe-N distances from the iron atom to the four coordinated N in the TIED ligand. The threshold edge positions shift about +1 eV from the iso-valence CH 3 CN, Cl − , and Br − complexes to their corresponding mixed-valence complexes. The relatively small shift compared with the normal +2 [special characters omitted] +3 eV edge shift from Fe 2+ to Fe 3+ reflects the oxidation state change of iron from Fe 2+ to Fe 2.5+ . The edge energy of the isovalence diiron complexes with different axial ligands increases in the order of the spectrochemical series of the axial Iigands from strong to weak field Iigands as follows [58, 59]: [special characters omitted] All the complexes studied here have a weak dipole-forbidden 1s → 3d pre-edge transition. The low intensity indicates only a small distortion of the octahedral coordination geometry of the central iron atom.

This thesis is devoted to study far-from-equilibrium aspects of quantum systems at strong coupling using the holographic duality as a tool. The duality, originated from string theory and further generalized to broader scenarios, relates certain strongly coupled gauge theories to classical gravity theories in higher dimensions. Over the last years, it has proved itself useful as a calculational tool to map difficult questions of interest in the gauge theory into a dual (i.e., equivalent) problem in a higher-dimensional gravity language where the solution may become feasible. The interest in strongly coupled quantum field theories, in particular non-Abelian gauge theories, is motivated by a number of nuclear and condensed matter physics phenomena which are known to take place at a non-perturbative regime, such as the quark-gluon plasma phase of quantum chromodynamics or high-Tc superconducting materials. While dealing with strong coupling is typically a very hard task even at equilibrium, the situation becomes yet more dramatic when non-equilibrium setups are concerned since the main non-perturbative tool available nowadays lattice field theory suffers from serious problems when it comes to real-time dynamics. This is the reason why unconventional techniques such as the ones provided by holography are welcome. Of particular interest here are the problems of thermalization of strongly coupled plasmas as well as the quench dynamics of quantum systems, both of which admit a dual gravitational description involving time-dependent solutions to the corresponding classical equations of motion in the bulk of Anti de Sitter (AdS) spacetimes, such as collapsing solutions describing AdS black hole formation. Specifically, and always from a holographic point of view, in this thesis we deal with three classes of problems: the thermalization properties of a charged non-Abelian plasma after a sudden injection of energy (such as a heavy ion collision); the dynamics of a symmetry breaking quench process from a relativistic to a non-relativistic setup of the Lifshitz type with dynamical exponent z; and, finally, a new analytical approach to the non- equilibrium properties of conformal field theory plasmas placed in an expanding background. Apart from the specific problems, we also provide a self-contained but concise introduction to the holographic duality with a view towards newcomers with an elementary general relativity and quantum field theory background. / Esta tese designa-se ao estudo de sistemas quânticos fortemente acoplados e fora do equilíbrio utilizando como ferramenta a dualidade holográfica. A dualidade, originária da teoria de cordas e posteriormente generalizada a cenários mais abrangentes, relaciona certas teorias de calibre fortemente acopladas e teorias de gravidade clássica em dimensões mais altas. Nos últimos anos, ela tem se mostrado útil como uma ferramenta de cálculo para mapear questões complicadas na teoria de gauge em um problema \\q{dual} (isto é, equivalente) formulado na linguagem completamente diferente de gravidade em dimensões extras, onde obter uma solução pode ser viável. O interesse em teorias quânticas de campo fortemente acopladas, em particular teorias de calibre não-Abelianas, motiva-se por uma variedade de fenômenos das físicas nuclear e da matéria condensada que, reconhecidamente, ocorrem em um regime não-perturbativo, tais como o plasma de quarks e glúons da cromodinâmica quântica ou certos materiais supercondutores com temperatura crítica alta. Em geral, lidar com acoplamentos fortes é uma tarefa bastante complicada mesmo em configurações de equilíbrio, mas a situação se torna ainda mais dramática quando configurações longe do equilíbrio são tratadas, visto que a principal ferramenta não-perturbativa disponível atualmente (teoria de campos na rede) enfrenta sérios problemas em situações dinâmicas. Esta é a principal razão pela qual técnicas alternativas tais como as fornecidas pela dualidade holográfica são bem vindas. De particular interesse aqui são os problemas da termalização de plasmas fortemente acoplados bem como a dinâmica pós-\\emph{quench} de sistemas quânticos, ambos os quais admitem uma descrição gravitacional dual envolvendo soluções dependentes do tempo às correspondentes equações gravitacionais em espaços-tempo de Anti de Sitter (AdS), tais como soluções de colapso descrevendo a formação de buracos negros assintoticamente AdS. Especificamente, e sempre sob um ponto de vista holográfico, nesta tese lidamos com três tipos diferentes de problemas: a termalização de um plasma não-Abeliano carregado como resultado de uma injeção repentina de energia (tal como uma colisão de íons pesados); a dinâmica durante um processo de quebra da simetria relativística para uma simetria não-relativística do tipo Lifshitz com expoente dinâmico $z$; e, finalmente, uma nova abordagem analítica para tratar propriedades fora do equílibrio de plasmas conformes colocados em um fundo que se expande. Além de tais problemas específicos, este texto fornece também uma introdução sucinta e auto-contida à dualidade holográfica direcionada a um leitor com conhecimento elementar de relatividade geral e teoria quântica de campos.