Дисертації з теми "Solvable models"

This Ph.D. thesis in mathematical physics concerns systems of interacting fermions with strong correlations. For these systems the physical properties can only be described in terms of the collective behavior of the fermions. Moreover, they are often characterized by a close competition between fermion localization versus delocalization, which can result in complex and exotic physical phenomena. Strongly correlated fermion systems are usually modelled by many-body Hamiltonians for which the kinetic- and interaction energy have the same order of magnitude. This makes them challenging to study as the application of conventional computational methods, like mean field- or perturbation theory, often gives unreliable results. Of particular interest are Hubbard-type models, which provide minimal descriptions of strongly correlated fermions. The research of this thesis focuses on such models defined on two-dimensional square lattices. One motivation for this is the so-called high-Tc problem of the cuprate superconductors. A main hypothesis is that there exists an underlying Fermi surface with nearly flat parts, i.e. regions where the surface is straight. It is shown that a particular continuum limit of the lattice system leads to an effective model amenable to computations. This limit is partial in that it only involves fermion degrees of freedom near the flat parts. The result is an effective quantum field theory that is analyzed using constructive bosonization methods. Various exactly solvable models of interacting fermions in two spatial dimensions are also derived and studied.
QC 20111207

For beta > 0, the beta-ensemble corresponds to the joint probability density on the real line proportional to prod_{n > m}^N abs{x_n - x_m}^beta prod_{n = 1}^N w(x_n) where w is the weight of the system. It has the application of being the Boltzmann factor for the configuration of N charge-one particles interacting logarithmically on an infinite wire inside an external field Q = -log w at inverse temperature beta. Similarly, the circular beta-ensemble has joint probability density proportional to prod_{n > m}^N abs{e^{itheta_n} - e^{itheta_m}}^beta prod_{n = 1}^N w(x_n) quad for theta_n in [- pi, pi) and can be interpreted as N charge-one particles on the unit circle interacting logarithmically with no external field. When beta = 1, 2, and 4, both ensembles are said to be solvable in that their correlation functions can be expressed in a form which allows for asymptotic calculations. It is not known, however, whether the general beta-ensemble is solvable. We present four families of particle models which are solvable point processes related to the beta-ensemble. Two of the examples interpolate between the circular beta-ensembles for beta = 1, 2, and 4. These give alternate ways of connecting the classical beta-ensembles besides simply changing the values of beta. The other two examples are "mirrored" particle models, where each particle has a paired particle reflected about some point or axis of symmetry.

This dissertation demonstrates the usefulness of exactly solvable quantum models in the investigation of light-matter interaction phenomena associated with the propagation of ultrashort laser pulses through gaseous media. This work fits into the larger research effort towards remedying the weaker portions of the standard set of medium modeling equations commonly used in simulations. The ultimate goal is to provide a self-consistent quantum mechanical description that can integrate Maxwell and Schrödinger systems and provide a means to realistically simulate nonlinear optical experiments on relevant scales. The study of exactly solvable models begins with one of the simplest quantum systems available, one with a 1D Dirac-delta function potential plus interaction with the light field. This model contains, in the simplest form, the most important "ingredients" that control optical filamentation, i.e. discrete and continuum electronic states. The importance of both states is emphasized in the optical intensity regime in which filaments form, where both kinds of electronic states simultaneously play a role and may not even be distinguishable. For this model atom, an analytical solution for the time-dependent light-induced atomic response from an arbitrary excitation waveform is obtained. Although this system is well-known and has been studied for decades, this result is probably the most practically useful and general one obtained thus far. Numerical implementation details of the result are also given as the task is far from trivial. Given an efficient implementation, the model is used in light-matter interaction simulations and from these it is apparent that even this toy model can qualitatively reproduce many of the nonlinear phenomena seen in experiments. Not only does this model capture the basic physics of optical filamentation, but it is also well-suited for high harmonic generation simulations. Next, a theoretical framework for using Stark resonant states (or metastable states) to represent the medium's polarization response is presented. Researchers have recognized long ago the utility of Gamow resonant states as a description of various decay processes. Even though a bound electron experiences a similar decay-like process as it transitions into the continuum upon ionization, it was unclear whether field-induced Stark resonant states carry physically relevant information. It is found that they do, and in particular it is possible to use them to capture a medium's polarization response. To this end, two quantum systems with potentials represented by a 1D Dirac-delta function and a 1D square well are solved, and all the necessary quantities for their use as medium models are presented. From these results it is possible to conjecture some general properties that hold for all resonance systems, including systems that reside in higher than one dimensional space. Finally, as a practical application of this theory, the Metastable Electronic State Approach (MESA) is presented as a quantum-based replacement for the standard medium modeling equations.

Intuitive arguments involving standard quantum mechanical uncertainty relations suggest that at length scales close to the Planck length, strong gravity effects limit the spatial as well as temporal resolution smaller than fundamental length scale, leading to space-space as well as spacetime uncertainties. Space-time cannot be probed with a resolution beyond this scale i.e. space-time becomes "fuzzy" below this scale, resulting into noncommutative spacetime. Hence it becomes important and interesting to study in detail the structure of such noncommutative spacetimes and their properties, because it not only helps us to improve our understanding of the Planck scale physics but also helps in bridging standard particle physics with physics at Planck scale. Our main focus in this thesis is to explore different methods of constructing models in these kind of spaces in higher dimensions. In particular, we provide a systematic procedure to relate a three dimensional q-deformed oscillator algebra to the corresponding algebra satisfied by canonical variables describing non-commutative spaces. The representations for the corresponding operators obey algebras whose uncertainty relations lead to minimal length, areas and volumes in phase space, which are in principle natural candidates of many different approaches of quantum gravity. We study some explicit models on these types of non-commutative spaces, in particular, we provide solutions of three dimensional harmonic oscillator as well as its decomposed versions into lower dimensions. Because the solutions are computed in these cases by utilising the standard Rayleigh-Schrodinger perturbation theory, we investigate a method afterwards to construct models in an exact manner. We demonstrate three characteristically different solvable models on these spaces, the harmonic oscillator, the manifestly non-Hermitian Swanson model and an intrinsically non-commutative model with Poschl-Teller type potential. In many cases the operators are not Hermitian with regard to the standard inner products and that is the reason why we use PT -symmetry and pseudo-Hermiticity property, wherever applicable, to make them self-consistent well designed physical observables. We construct an exact form of the metric operator, which is rare in the literature, and provide Hermitian versions of the non-Hermitian Euclidean Lie algebraic type Hamiltonian systems. We also indicate the region of broken and unbroken PT -symmetry and provide a theoretical treatment of the gain loss behaviour of these types of systems in the unbroken PT -regime, which draws more attention to the experimental physicists in recent days. Apart from building mathematical models, we focus on the physical implications of noncommutative theories too. We construct Klauder coherent states for the perturbative and nonperturbative noncommutative harmonic oscillator associated with uncertainty relations implying minimal lengths. In both cases, the uncertainty relations for the constructed states are shown to be saturated and thus imply to the squeezed coherent states. They are also shown to satisfy the Ehrenfest theorem dictating the classical like nature of the coherent wavepacket. The quality of those states are further underpinned by the fractional revival structure which compares the quality of the coherent states with that of the classical particle directly. More investigations into the comparison are carried out by a qualitative comparison between the dynamics of the classical particle and that of the coherent states based on numerical techniques. We find the qualitative behaviour to be governed by the Mandel parameter determining the regime in which the wavefunctions evolve as soliton like structures. We demonstrate these features explicitly for the harmonic oscillator, the Poschl-Teller potential and a Calogero type potential having singularity at the origin, we argue on the fact that the effects are less visible from the mathematical analysis and stress that the method is quite useful for the precession measurement required for the experimental purpose. In the context of complex classical mechanics we also find the claim that "the trajectories of classical particles in complex potential are always closed and periodic when its energy is real, and open when the energy is complex", which is demanded in the literature, is not in general true and we show that particles with complex energies can possess a closed and periodic orbit and particles with real energies can produce open trajectories.

Nanoscale systems have sizes intermediate between atomic and macroscopic ones. Therefore their treatment often requires a combination of methods from atomic and condensed matter physics. The conventional Landau-Zener theory, being a powerful tool in atomic physics, often fails to predict correctly nonadiabatic transition probabilities in various nanostructures because it does not include many-body effects typical for mesoscopics. In this research project the generalizations of the Landau-Zener theory that solve this problem were studied. The multistate, multiparticle and nonunitary extensions of the theory have been proposed and investigated. New classes of exactly solvable models have been derived. I discuss their applications in problems of the molecular condensate dissociation and of the driven charge transport. In application to the physics of nanomagnets new approaches in modeling the influence of the environment on the Landau-Zener evolution are proposed and simple universal formulas are derived for the extensions of the theory that include the coupling to noise and the nuclear spin bath.

This thesis is devoted to quantum confinement effects in low-dimensional Dirac materials. We propose a variety of schemes in which massless Dirac fermions, which are notoriously diffcult to manipulate, can be trapped in a bound state. Primarily we appeal for the use of external electromagnetic fields. As a consequence of this endeavor, we find several interesting condensed matter analogues to effects from relativistic quantum mechanics, as well as entirely new effects and a possible novel state of matter. For example, in our study of the effective Coulomb interaction in one dimension, we demonstrate how atomic collapse may arise in carbon nanotubes or graphene nanoribbons, and describe the critical importance of the size of the band gap. Meanwhile, inspired by groundbreaking experiments investigating the effects of strain, we propose how to confine the elusive charge carriers in so-called velocity barriers, which arise due to a spatially inhomogeneous Fermi velocity triggered by a strained lattice. We also present a new and beautiful quasi-exactly solvable model of quantum mechanics, showing the possibilities for confinement in magnetic quantum dots are not as stringent as previously thought. We also reveal that Klein tunnelling is not as pernicious as widely believed, as we show bound states can arise from purely electrostatic means at the Dirac point energy. Finally, we show from an analytical solution to the quasi-relativistic two-body problem, how an exotic same-particle paring can occur and speculate on its implications if found in the laboratory.

An exact quantum Monte Carlo algorithm for interacting particles in the spatial continuum is extended to exploit the massive parallelism offered by graphics processing units. Its efficacy is tested on the Calogero-Sutherland model describing a system of bosons interacting in one spatial dimension via an inverse square law. Due to the long range nature of the interactions, this model has proved difficult to simulate via conventional path integral Monte Carlo methods running on conventional processors. Using Graphics Processing Units, optimal speedup factors of up to 640 times are obtained for N = 126 particles. The known results for the ground state energy are confirmed and, for the first time, the effects of thermal fluctuations at finite temperature are explored.

Cette thèse porte sur l'étude de système quantique intégrable spécifique ``chaînes de spin'' présentant différentes symétries. Ces chaînes de spin sont considérées comme des modèles jouets de certaines théories bidimensionnelles des champs lorsque la taille de ces modèles est finie. En particulier, certaines relations fonctionnelles dans ces chaînes de spin ont été généralisées aux théories des champs en utilisant un nombre fini d'équations pour trouver leur spectre.Nous commençons cette thèse en décrivant la chaîne de spins rationnelle bien étudiée avec symétrie GL(n) en utilisant l'opérateur de ``codérivée'' pour construire un « opérateur Q » polynomial qui nous permet de diagonaliser l'hamiltonien. Nous montrons l'équivalence avec une autre construction s'appuyant sur des représentations explicites en termes d’oscillateurs harmoniques.Nous étudions ensuite une chaîne de spins moins connue présentant une symétrie SO(2r). Nous construisons le ``Q-opérateur'' pour les représentations connues. Nous essayons ensuite plusieurs méthodes pour construire lesdits opérateurs pour des représentations générales. Ces tentatives montrent clairement que, d’une part, elles suggèrent fortement que la codérivative n’est pas suffisante pour décrire des représentations générales dans l’espace auxiliaire. Nous espérons en revanche qu’ils aideront à trouver quels outils supplémentaires pourraient nous permettre de les décrire
This thesis is concerned with the study of specific integrable quantum system ``spin chains'' with different symmetries. These spin chains are considered toy models of some two-dimensional field theories when the size of these models is finite. In particular, some functional relations in these spin chains were generalized to field theories using a finite number of equations to find their spectrum.We start this thesis by describing the well-studied rational spin chain with GL(n) symmetry using the Coderivative operator to build a polynomial ``Q-operator'' that allows us to diagonalize the Hamiltonian. We show the equivalence with another construction relying on representations that are explicit in terms of harmonic oscillators.We then study a lesser-known spin chain with SO(2r) symmetry. We build the ``Q-operator'' for the known representations. Then we attempt several methods to build said operators for general representations. These attempts clearly show that, on the one hand, the attempts strongly suggest the Coderivative is not sufficient to describe general representations in auxiliary space. On the other hand, we hope they will help to find what additional tools may allow us to describe them

Cette thèse présente plusieurs aspects de la physique des systèmes élastiques désordonnés et des méthodes analytiques utilisées pour les étudier. On s’intéressera d’une part aux propriétés universelles des processus d’avalanches statiques et dynamiques (à la transition de dépiégeage) d’interfaces élastiques de dimension arbitraire en milieu aléatoire à température nulle. Pour étudier ces questions nous utiliserons le groupe de renormalisation fonctionnel. Après une revue de ces aspects,nous présenterons plus particulièrement les résultats obtenus pendant la thèse sur (i) la structure spatiale des avalanches et (ii) les corrélations entre avalanches.On s’intéressera d’autre part aux propriétés statiques à température finie de polymères dirigés en dimension 1+1, et en particulier aux observables liées à la classe d’universalité KPZ. Dans ce contexte l’étude de modèles exactement solubles a récemment permis de grands progrès. Après une revue de ces aspects, nous nous intéresserons plus particulièrement aux modèles exactement solubles de polymère dirigé sur le réseau carré, et présenterons les résultats obtenus pendantla thèse dans cette voie: (i) classification des modèles à température finie sur le réseau carré exactement solubles par ansatz de Bethe; (ii) universalité KPZ pour les modèles Log-Gamma et Inverse-Beta; (iii) universalité et nonuniversalitéKPZ pour le modèle Beta; (iv) mesures stationnaires du modèle Inverse-Beta et des modèles à température nulle associés
This thesis presents several aspects of the physics of disordered elastic systems and of the analytical methods used for their study.On one hand we will be interested in universal properties of avalanche processes in the statics and dynamics (at the depinning transition) of elastic interfaces of arbitrary dimension in disordered media at zero temperature. To study these questions we will use the functional renormalization group. After a review of these aspects we will more particularly present the results obtained during the thesis on (i) the spatial structure of avalanches and (ii) the correlations between avalanches.On the other hand we will be interested in static properties of directed polymers in 1+1 dimension, and in particular in observables related to the KPZ universality class. In this context the study of exactly solvable models has recently led to important progress. After a review of these aspects we will be more particularly interested in exactly solvable models of directed polymer on the square lattice and present the results obtained during the thesis in this direction: (i) classification ofBethe ansatz exactly solvable models of directed polymer at finite temperature on the square lattice; (ii) KPZ universality for the Log-Gamma and Inverse-Beta models; (iii) KPZ universality and non-universality for the Beta model; (iv) stationary measures of the Inverse- Beta model and of related zero temperature models

In this thesis, we study the non-Abelian anyons that emerge as vortices in Ki-taev's honeycomb spin lattice model. By generalizing the solution of the model, we explicity demonstrate the non-Abelian fusion rules and the braid statistics that charaterize the anyons. This is based on showing the presence of vortices leads to zero modes in the spectrum. These can acquire finite energy due to short range vortex-vortex interactions. By studying the spectral evolution as a function of the vortex seperation, we unambigously identify the zero modes with the fusion degrees of freedom of non-Abelian anyons. To calculate the non-Abelian statistics, we show how the vortex transport can be implemented through local manipulation of the couplings. This enables us to employ the eigenstates of the model to simulate a process where a vortex winds around another. The corresponding evolution of the degenerate ground state space is given by a Berry phase, which under suitable conditions coincides with the statistics. By considering a range of finite size systems, we find a physical regime where the Berry phase gives the predicted statistics of the anoyonic vortices with high fidelity. Finally we study the full-vortex sector of the model and find that is supports a previously undiscovered topological phase. This new phase emerges from the phase with non-Abelian anyons due to their interactions. To study the transitions between the different topological phases appearing in the model, we consider Fermi surface, whose topology captures the long-range properties. Each phase is found to be characterized by a distinct number of Fermi points, with the number depending on distinct global Hamiltonian symmetries. To study how the Fermi surfaces evolve into each other at phase transitions, we consider the low-energy field theory that is described by Dirac fermions. We show that phase transition driving perturbations translate to a coupling to chiral gauge fields, that always lead to Fermi point transport. By studying this transport, we obtain analytically the extended phase space of the model and its properties.

Solvate formation is a phenomenon that has received special attention in solid state chemistry over the past few years. This is due to its potential to both improve and impair pharmaceutical formulations. The reasons for solvate formation aren’t explicitly known. Therefore, there is currently no reliable guide in the literature on what solvents to choose in order to avoid or form a solvate when crystallizing an organic material. In this thesis we address the problem by trying to find the main reasons of solvate formation. A knowledge-based approach was used to link the molecular structure of an organic compound to its ability to form a solvate with five different solvents; these are ethanol, methanol, dichloromethane, chloroform and water. The Cambridge Structural Database (CSD) was used as a source of information for this study. A supervised machine learning method, logistic regression was found to be the optimal method for fitting these knowledge-based models. The result was one predictive model per solvent, with a success rate of 74-80 %. Each model incorporated two molecular descriptors, representing two molecular features of molecules. These are the size and branching in addition to hydrogen bonding ability. The models’ predictive ability was validated via experimental work, in which slurries of 10 pharmaceutically active ingredients were screened for solvate formation with each of the five solvents in the study. During the screening process, a new diflunisal dichloromethane solvate, a diflunisal chloroform solvate and a hymercromone methanol solvate were found. The PXRD patterns of these forms are reported. The thesis also includes SCXRD analysis of a previously known grisoefulvin dichloromethane solvate, a previously known fenofibrate polymorph and a new fenofibrate polymorph.

Cette thèse de doctorat porte sur l'étude du modèle de croissance stochastique Kardar-Parisi-Zhang (KPZ) en 1+1 dimensions et en particulier de l'équation qui le régit. Cette thèse est d'une part destinée à effectuer un état de l'art et dresser un portrait moderne de la recherche des solutions exactes de l'équation KPZ, de leurs propriétés en terme de théorie des grandes déviations et également de leurs applications (en théorie des matrices aléatoires ou en calcul stochastique notamment). D'autre part cette thèse a pour but de formuler un certain nombre de questions ouvertes à l'interface avec la théorie de l'intégrabilité, la théorie des matrices aléatoires et la théorie des gaz de Coulomb.Cette thèse est divisée en trois parties distinctes portant (i) sur les solutions exactes de l'équation KPZ, (ii) sur les solutions à temps court sous la forme d'un principe grandes déviations et (iii) sur les solutions à temps long et leurs extensions aux statistiques linéaires au bord de spectre de matrice aléatoire.Nous présenterons les résultats de cette thèse comprenant notamment (a) une nouvelle solution de l'équation KPZ à tout temps dans un demi-espace, (b) une méthodologie générale pour établir à temps court un principe de grandes déviations pour les solutions de KPZ à partir de leur représentation sous forme de déterminant de Fredholm et (c) une unification de quatre méthodes permettant d'obtenir à temps long un principe de grandes déviations pour les solutions de l'équation KPZ et de manière plus générale d'étudier des statistiques linéaires au bord du spectre de matrices aléatoires
Throughout this Ph.D thesis, we will study the Kardar-Parisi-Zhang (KPZ) stochastic growth model in 1+1 dimensions and more particularly the equation which governs it. The goal of this thesis is two-fold. Firstly, it aims to review the state of the art and to provide a detailed picture of the search of exact solutions to the KPZ equation, of their properties in terms of large deviations and also of their applications to random matrix theory or stochastic calculus. Secondly, is it intended to express a certain number of open questions at the interface with integrability theory, random matrix theory and Coulomb gas theory.This thesis is divided in three distinct parts related to (i) the exact solutions to the KPZ equation, (ii) the short time solutions expressed by a Large Deviation Principle and the associated rate functions and (iii) the solutions at large time and their extensions to linear statistics at the edge of random matrices.We will present the new results of this thesis including (a) a new solution to the KPZ equation at all times in a half-space, (b) a general methodology to establish at short time a Large Deviation Principle for the solutions to the KPZ equation from their representation in terms of Fredholm determinant and (c) the unification of four methods allowing to obtain at large time a Large Deviation Principle for the solution to the KPZ equation and more generally to investigate linear statistics at the soft edge of random matrices

The critical phases of two dimensional lattice models are widely believed to be described by conformal quantum field theories in the scaling limit. In the past few years, formal proofs of the conformal invariance in different formulations of the Ising model have emerged which make pivotal use of some complex lattice observables. Due to their distinctive property of discrete holomorphicity, they are considered to be the lattice counterpart of holomorphic currents in the field theories. In this thesis, we study a weakened form of discrete holomorphicity that is known to be obeyed by natural generalizations of these observables to three important families of solvable models. The main result of this thesis is that discrete holomorphicity can be seen as a requirement stronger than the conditions of integrability of the models. That is, these conditions, the inversion relations and the Yang-Baxter equations, can be derived from this form of lattice holomorphicity. This finding is proposed as an explanation for the remarkable observation that discrete holomorphicity holds only on the integrable critical manifold of the weights. For the self-dual models, the duality conditions can also be established similarly. A key role in this argument is played by the rhombic embeddings of Baxter lattices. It is noted that, by the requirement of holomorphicity on every rhombus, the conformal spins of the observables are restricted to a discrete spectrum that label the solutions in which the angles of the rhombuses are interpreted as re-scaled spectral parameters. This interpretation allows the relationships between the spectral parameters in the integrability conditions to be seen as the criteria for geometric consistency of the rhombic embedding. The crossing symmetry of the models is then related to the alignment of the rhombuses with respect to the rapidity lines. It has also been shown here that values of the observables on the boundary of a simply connected domain remain unchanged by local rearrangement of rhombuses due to the Z-invariance of the models. This provides an independent characterization of the observables besides discrete holomorphicity and enables us to define them on the equivalence class of Baxter lattices with any given braiding of the rapidity lines. For an equivalence class, the holomorphicity equations then provide linear relations among its partition functions with different boundary conditions. The results of this thesis thus point to the essential, albeit somewhat obscure, role of integrability in the rigorous proofs.

abstract: In the traditional setting of quantum mechanics, the Hamiltonian operator does not depend on time. While some Schrödinger equations with time-dependent Hamiltonians have been solved, explicitly solvable cases are typically scarce. This thesis is a collection of papers in which this first author along with Suslov, Suazo, and Lopez, has worked on solving a series of Schrödinger equations with a time-dependent quadratic Hamiltonian that has applications in problems of quantum electrodynamics, lasers, quantum devices such as quantum dots, and external varying fields. In particular the author discusses a new completely integrable case of the time-dependent Schrödinger equation in R^n with variable coefficients for a modified oscillator, which is dual with respect to the time inversion to a model of the quantum oscillator considered by Meiler, Cordero-Soto, and Suslov. A second pair of dual Hamiltonians is found in the momentum representation. Our examples show that in mathematical physics and quantum mechanics a change in the direction of time may require a total change of the system dynamics in order to return the system back to its original quantum state. The author also considers several models of the damped oscillators in nonrelativistic quantum mechanics in a framework of a general approach to the dynamics of the time-dependent Schrödinger equation with variable quadratic Hamiltonians. The Green functions are explicitly found in terms of elementary functions and the corresponding gauge transformations are discussed. The factorization technique is applied to the case of a shifted harmonic oscillator. The time-evolution of the expectation values of the energy related operators is determined for two models of the quantum damped oscillators under consideration. The classical equations of motion for the damped oscillations are derived for the corresponding expectation values of the position operator. Finally, the author constructs integrals of motion for several models of the quantum damped oscillators in a framework of a general approach to the time-dependent Schrödinger equation with variable quadratic Hamiltonians. An extension of the Lewis-Riesenfeld dynamical invariant is given. The time-evolution of the expectation values of the energy related positive operators is determined for the oscillators under consideration. A proof of uniqueness of the corresponding Cauchy initial value problem is discussed as an application.
Dissertation/Thesis
Ph.D. Applied Mathematics for the Life and Social Sciences 2011

In this thesis, we present three projects studying exactly solvable models in the KPZ universality class and one project studying a generalization of the SIR model from epidemiology. The first chapter gives an overview of the results and how they fit into the study of KPZ universality when applicable. Each of the following 4 chapters corresponds to a published or submitted article. In the first project, we study an oriented first passage percolation model for the evolution of a river delta. We show that at any fixed positive time, the width of a river delta of length L approaches a constant times L²/³ with Tracy-Widom GUE fluctuations of order L⁴/⁹. This result can be rephrased in terms of a particle system generalizing pushTASEP. We introduce an exactly solvable particle system on the integer half line and show that after running the system for only finite time the particle positions have Tracy-Widom fluctuations. In the second project, we study n-point sticky Brownian motions: a family of n diffusions that evolve as independent Brownian motions when they are apart, and interact locally so that the set of coincidence times has positive Lebesgue measure with positive probability. These diffusions can also be seen as n random motions in a random environment whose distribution is given by so-called stochastic flows of kernels. For a specific type of sticky interaction, we prove exact formulas characterizing the stochastic flow and show that in the large deviations regime, the random fluctuations of these stochastic flows are Tracy-Widom GUE distributed. An equivalent formulation of this result states that the extremal particle among n sticky Brownian motions has Tracy-Widom distributed fluctuations in the large n and large time limit. These results are proved by viewing sticky Brownian motions as a diffusive limit of the exactly solvable beta random walk in random environment. In the third project, we study a class of probability distributions on the six-vertex model, which originates from the higher spin vertex model. For these random six-vertex models we show that the behavior near their base is asymptotically described by the GUE-corners process. In the fourth project, we study a model for the spread of an epidemic. This model generalizes the classical SIR model to account for inhomogeneity in the infectiousness and susceptibility of individuals in the population. A first statement of this model is given in terms of infinitely many coupled differential equations. We show that solving these equations can be reduced to solving a one dimensional first order ODE, which is easy to solve numerically. We use the explicit form of this ODE to characterize the total number of people who are ever infected before the epidemic dies out. This model is not related to the KPZ universality class.

In this thesis, we study gapped topological phases of matter in systems with strong inter-particle interaction. They are challenging to analyze theoretically, because interaction not only gives rise to a plethora of phases that are otherwise absent, but also renders methods used to analyze non-interacting systems inadequate. By now, people have had a relatively systematic understanding of topological orders in two spatial dimensions. However, less is known about the higher dimensional cases. In Chapter 2, we will explore three dimensional long-range entangled topological orders in the framework of Walker-Wang models, which are a class of exactly solvable models for three-dimensional topological phases that are not known previously to be able to capture these phases. We find that they can represent a class of twisted discrete gauge theories, which were discovered using a different formalism. Meanwhile, a systematic theory of bosonic symmetry protected topological (SPT) phases in all spatial dimensions have been developed based on group cohomology. A generalization of the theory to group supercohomology has been proposed to classify and characterize fermionic SPT phases in all dimensions. However, it can only handle cases where the symmetry group of the system is a product of discrete unitary symmetries. Furthermore, the classification is known to be incomplete for certain symmetries. In Chapter 3, we will construct an exactly solvable model for the two-dimensional time-reversal-invariant topological superconductors, which could be valuable as a first attempt to a systematic understanding of strongly interacting fermionic SPT phases with anti-unitary symmetries in terms of exactly solvable models. In Chapter 4, we will propose an alternative classification of fermionic SPT phases using the spin cobordism theory, which hopefully can capture all the phases missing in the supercohomology classification. We test this proposal in the case of fermionic SPT phases with Z₂ symmetry, where Z₂ is either time-reversal or an internal symmetry. We find that cobordism classification correctly describes all known fermionic SPT phases in space dimensions less than or equal to 3.

In this dissertation, two exactly solvable models from the Kitaev class [Ann. Phys. 321, 2 (2006)] of exactly solvable models are analysed. In the second chapter, Kitaev models and their generic properties are reviewed. Majorana fermions are introduced and discussed. Then their relationship with the solution of Kitaev models are discussed which involves the emergence of a Z₂ gauge symmetry and anyonic particles of both Abelian and non-Abelian varieties. The third chapter, which is based on the research article [Phys. Rev. B (Rapid Comm.) 83, (2011)], examines the Kitaev model on the kagome lattice. A rich phase diagram of this model is found to include a topological (gapped) chiral spin liquid with gapless chiral edge states, and a gapless chiral spin liquid phase with a spin Fermi surface. The ground state of the current model contains an odd number of electrons per unit cell which qualitatively distinguishes it from previously studied exactly solvable models with a spin Fermi surface. Moreover, it is shown that the spin Fermi surface is stable against weak perturbations. The fourth chapter is based on the article [Phys. Rev. B 84,(2011)] and analyses a disordered generalisation of the Yao-Kivelson [Phys. Rev. Lett. 99,247203 (2007)] chiral spin-liquid on the decorated honeycomb lattice. The model is generalised by the inclusion of random exchange couplings. The phase diagram was determined and it is found that disorder enlarges the region of the topological non-Abelian phase with finite Chern number. A study of the energy level statistics as a function of disorder and other parameters in the Hamiltonian show that the phase transition between the non-Abelian and Abelian phases of the model at large disorder can be associated with pair annihilation of extended states at zero energy. Analogies to integer quantum Hall systems, topological Anderson insulators, and disordered topological Chern insulators are discussed.
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Title: Stochastic dynamics and energetics of biomolecular systems Author: Artem Ryabov Department: Department of Macromolecular Physics Supervisor: prof. RNDr. Petr Chvosta, CSc., Department of Macromolecular Physics Abstract: The thesis comprises exactly solvable models from non-equilibrium statistical physics. First, we focus on a single-file diffusion, the diffusion of particles in narrow channel where particles cannot pass each other. After a brief review, we discuss open single-file systems with absorbing boundaries. Emphasis is put on an interplay of absorption process at the boundaries and inter-particle entropic repulsion and how these two aspects affect the dynam- ics of a given tagged particle. A starting point of the discussions is the exact distribution for the particle displacement derived by order-statistics argu- ments. The second part of the thesis is devoted to stochastic thermodynam- ics. In particular, we present an exactly solvable model, which describes a Brownian particle diffusing in a time-dependent anharmonic potential. The potential has a harmonic component with a time-dependent force constant and a time-independent repulsive logarithmic barrier at the origin. For a particular choice of the driving protocol, the exact work characteristic func- tion is obtained. An asymptotic analysis of...

Cette thèse porte sur l’étude des familles de polynômes orthogonaux et leurs liens avec les modèles exactement résolubles. Elle se décline en deux parties. Dans la première, on caractérise quatre nouvelles familles de polynômes orthogonaux à l’aide de processus limites appliqués à des familles appartenant aux schéma d’Askey et de Bannai-Ito. Des troncations singulières des polynômes de Wilson et d’Askey-Wilson sont considérées. Deux premières extensions bivariées de polynômes appartenant au tableau de Bannai-Ito sont également introduites. La deuxième partie présente quatre modèles exactement résolubles en lien avec la théorie des polynômes orthogonaux. Les propriétés de transfert parfait d’information quantique et de partage d’intrication d’un modèle de chaîne de spin XX dont les couplage sont liés aux polynômes de para-Racah sont examinées. Deux modèles superintégrables contenant des opérateurs de réflexions sont proposés. Leurs solutions sont obtenues et leurs symétries s’encodent respectivement dans l’algèbre de Bannai-Ito de rang deux et de rang arbitraire ce qui mène à conjecturer l’apparition des polynômes de Bannai-Ito multivariés comme coefficients de connection. Finalement, par la théorie des représentations de la superalgèbre osp(1|2), deux identités de convolution pour des familles de polynômes du tableau de Bannai-Ito sont offertes. Une réalisation en termes d’opérateurs de Dunkl conduit à une fonction génératrice bilinéaire pour les polynômes de Big −1 Jacobi.
This thesis is concerned with the study of families of orthogonal polynomials and their connection to exactly solvable models. It comprises two parts. In the first one, four novel families of orthogonal polynomials are caracterized through limit processes applied to families belonging to the Askey and Bannai-Ito schemes. Singular truncations of the Wilson and Askey-Wilson polynomials are considered. The first two bivariate extensions of families of the Bannai-Ito tableau are also introduced. The second part presents four exactly solvable models connected to the theory of orthogonal polynomials. The perfect transfer of quantum information and entanglement generation properties of an XX spin chain model whose couplings are linked to the para-Racah polynomials are examined. Two superintegrable models containing reflexion operators are proposed. Their solutions are obtained and their symmetries are encoded respectively in the rank two and arbitrary rank Bannai-Ito algebra which leads to conjecture the apparition of multivariate Bannai-Ito polynomials as overlaps. Finally, via the representation theory of the osp(1|2) Lie superalgebra, two convolution identities for families of orthogonal polynomials of the Bannai-Ito tableau are offered. Realizations in terms of Dunkl operators lead to a bilinear generating function for the Big −1 Jacobi polynomials.

The aim of this thesis is to investigate the Zamolodchikov model by using the equivalence to the sl(n)-chiral Potts model. The Zamolodchikov model is a three-dimensional exactly solvable model. It was constructed by Baxter[4] according to the solution of the tetrahedron equation obtained by Zamolodchikov[31]. In particular, we considered the minimum non-trivial case, the three-layer model Zamolodchikov model. Using the equivalency, we constructed the general Boltzmann weights and transfer matrices of the sl(3)-chiral Potts model. We also analysed the commutation relations by using the “starstar” relation[6] and found that the relations are shifted by one spin along the chain in the horizontal direction. The functional relations of the eigenvalues of transfer matrices were constructed by generalizing the results from paper [11] and [10]. It was noticed that the shifted relations forbid us from using the methods of studying the homogeneous Zamolodchikov model. The Bethe ansatz equations were derived for general three-layer Zamolodchikov model and simplified for some particular cases.