Dirty Tricks for Statistical Mechanics
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2D Potts Model Correlation Lengths
KOMA Revised version May D Potts Mo del Correlation Lengths Numerical Evidence for = at o d t Wolfhard Janke and Stefan Kappler Institut f ur Physik Johannes GutenbergUniversitat Mainz Staudinger Weg Mainz Germany Abstract We have studied spinspin correlation functions in the ordered phase of the twodimensional q state Potts mo del with q and at the rstorder transition p oint Through extensive Monte t Carlo simulations we obtain strong numerical evidence that the cor relation length in the ordered phase agrees with the exactly known and recently numerically conrmed correlation length in the disordered phase As a byproduct we nd the energy moments o t t d in the ordered phase at in very go o d agreement with a recent large t q expansion PACS numbers q Hk Cn Ha hep-lat/9509056 16 Sep 1995 Introduction Firstorder phase transitions have b een the sub ject of increasing interest in recent years They play an imp ortant role in many elds of physics as is witnessed by such diverse phenomena as ordinary melting the quark decon nement transition or various stages in the evolution of the early universe Even though there exists already a vast literature on this sub ject many prop erties of rstorder phase transitions still remain to b e investigated in detail Examples are nitesize scaling FSS the shap e of energy or magnetization distributions partition function zeros etc which are all closely interrelated An imp ortant approach to attack these problems are computer simulations Here the available system sizes are necessarily -
Full and Unbiased Solution of the Dyson-Schwinger Equation in the Functional Integro-Differential Representation
PHYSICAL REVIEW B 98, 195104 (2018) Full and unbiased solution of the Dyson-Schwinger equation in the functional integro-differential representation Tobias Pfeffer and Lode Pollet Department of Physics, Arnold Sommerfeld Center for Theoretical Physics, University of Munich, Theresienstrasse 37, 80333 Munich, Germany (Received 17 March 2018; revised manuscript received 11 October 2018; published 2 November 2018) We provide a full and unbiased solution to the Dyson-Schwinger equation illustrated for φ4 theory in 2D. It is based on an exact treatment of the functional derivative ∂/∂G of the four-point vertex function with respect to the two-point correlation function G within the framework of the homotopy analysis method (HAM) and the Monte Carlo sampling of rooted tree diagrams. The resulting series solution in deformations can be considered as an asymptotic series around G = 0 in a HAM control parameter c0G, or even a convergent one up to the phase transition point if shifts in G can be performed (such as by summing up all ladder diagrams). These considerations are equally applicable to fermionic quantum field theories and offer a fresh approach to solving functional integro-differential equations beyond any truncation scheme. DOI: 10.1103/PhysRevB.98.195104 I. INTRODUCTION was not solved and differences with the full, exact answer could be seen when the correlation length increases. Despite decades of research there continues to be a need In this work, we solve the full DSE by writing them as a for developing novel methods for strongly correlated systems. closed set of integro-differential equations. Within the HAM The standard Monte Carlo approaches [1–5] are convergent theory there exists a semianalytic way to treat the functional but suffer from a prohibitive sign problem, scaling exponen- derivatives without resorting to an infinite expansion of the tially in the system volume [6]. -
Notes on Statistical Field Theory
Lecture Notes on Statistical Field Theory Kevin Zhou [email protected] These notes cover statistical field theory and the renormalization group. The primary sources were: • Kardar, Statistical Physics of Fields. A concise and logically tight presentation of the subject, with good problems. Possibly a bit too terse unless paired with the 8.334 video lectures. • David Tong's Statistical Field Theory lecture notes. A readable, easygoing introduction covering the core material of Kardar's book, written to seamlessly pair with a standard course in quantum field theory. • Goldenfeld, Lectures on Phase Transitions and the Renormalization Group. Covers similar material to Kardar's book with a conversational tone, focusing on the conceptual basis for phase transitions and motivation for the renormalization group. The notes are structured around the MIT course based on Kardar's textbook, and were revised to include material from Part III Statistical Field Theory as lectured in 2017. Sections containing this additional material are marked with stars. The most recent version is here; please report any errors found to [email protected]. 2 Contents Contents 1 Introduction 3 1.1 Phonons...........................................3 1.2 Phase Transitions......................................6 1.3 Critical Behavior......................................8 2 Landau Theory 12 2.1 Landau{Ginzburg Hamiltonian.............................. 12 2.2 Mean Field Theory..................................... 13 2.3 Symmetry Breaking.................................... 16 3 Fluctuations 19 3.1 Scattering and Fluctuations................................ 19 3.2 Position Space Fluctuations................................ 20 3.3 Saddle Point Fluctuations................................. 23 3.4 ∗ Path Integral Methods.................................. 24 4 The Scaling Hypothesis 29 4.1 The Homogeneity Assumption............................... 29 4.2 Correlation Lengths.................................... 30 4.3 Renormalization Group (Conceptual).......................... -
10 Basic Aspects of CFT
10 Basic aspects of CFT An important break-through occurred in 1984 when Belavin, Polyakov and Zamolodchikov [BPZ84] applied ideas of conformal invariance to classify the possible types of critical behaviour in two dimensions. These ideas had emerged earlier in string theory and mathematics, and in fact go backto earlier (1970) work of Polyakov [Po70] in which global conformal invariance is used to constrain the form of correlation functions in d-dimensional the- ories. It is however only by imposing local conformal invariance in d =2 that this approach becomes really powerful. In particular, it immediately permitted a full classification of an infinite family of conformally invariant theories (the so-called “minimal models”) having a finite number of funda- mental (“primary”) fields, and the exact computation of the corresponding critical exponents. In the aftermath of these developments, conformal field theory (CFT) became for some years one of the most hectic research fields of theoretical physics, and indeed has remained a very active area up to this date. This chapter focusses on the basic aspects of CFT, with a special emphasis on the ingredients which will allow us to tackle the geometrically defined loop models via the so-called Coulomb Gas (CG) approach. The CG technique will be exposed in the following chapter. The aim is to make the presentation self- contained while remaining rather brief; the reader interested in more details should turn to the comprehensive textbook [DMS87] or the Les Houches volume [LH89]. 10.1 Global conformal invariance A conformal transformation in d dimensions is an invertible mapping x x′ → which multiplies the metric tensor gµν (x) by a space-dependent scale factor: gµ′ ν (x′)=Λ(x)gµν (x). -
Arxiv:1509.06955V1 [Physics.Optics]
Statistical mechanics models for multimode lasers and random lasers F. Antenucci 1,2, A. Crisanti2,3, M. Ib´a˜nez Berganza2,4, A. Marruzzo1,2, L. Leuzzi1,2∗ 1 NANOTEC-CNR, Institute of Nanotechnology, Soft and Living Matter Lab, Rome, Piazzale A. Moro 2, I-00185, Roma, Italy 2 Dipartimento di Fisica, Universit`adi Roma “Sapienza,” Piazzale A. Moro 2, I-00185, Roma, Italy 3 ISC-CNR, UOS Sapienza, Piazzale A. Moro 2, I-00185, Roma, Italy 4 INFN, Gruppo Collegato di Parma, via G.P. Usberti, 7/A - 43124, Parma, Italy We review recent statistical mechanical approaches to multimode laser theory. The theory has proved very effective to describe standard lasers. We refer of the mean field theory for passive mode locking and developments based on Monte Carlo simulations and cavity method to study the role of the frequency matching condition. The status for a complete theory of multimode lasing in open and disordered cavities is discussed and the derivation of the general statistical models in this framework is presented. When light is propagating in a disordered medium, the system can be analyzed via the replica method. For high degrees of disorder and nonlinearity, a glassy behavior is expected at the lasing threshold, providing a suggestive link between glasses and photonics. We describe in details the results for the general Hamiltonian model in mean field approximation and mention an available test for replica symmetry breaking from intensity spectra measurements. Finally, we summary some perspectives still opened for such approaches. The idea that the lasing threshold can be understood as a proper thermodynamic transition goes back since the early development of laser theory and non-linear optics in the 1970s, in particular in connection with modulation instability (see, e.g.,1 and the review2). -
Arxiv:1910.10745V1 [Cond-Mat.Str-El] 23 Oct 2019 2.2 Symmetry-Protected Time Crystals
A Brief History of Time Crystals Vedika Khemania,b,∗, Roderich Moessnerc, S. L. Sondhid aDepartment of Physics, Harvard University, Cambridge, Massachusetts 02138, USA bDepartment of Physics, Stanford University, Stanford, California 94305, USA cMax-Planck-Institut f¨urPhysik komplexer Systeme, 01187 Dresden, Germany dDepartment of Physics, Princeton University, Princeton, New Jersey 08544, USA Abstract The idea of breaking time-translation symmetry has fascinated humanity at least since ancient proposals of the per- petuum mobile. Unlike the breaking of other symmetries, such as spatial translation in a crystal or spin rotation in a magnet, time translation symmetry breaking (TTSB) has been tantalisingly elusive. We review this history up to recent developments which have shown that discrete TTSB does takes place in periodically driven (Floquet) systems in the presence of many-body localization (MBL). Such Floquet time-crystals represent a new paradigm in quantum statistical mechanics — that of an intrinsically out-of-equilibrium many-body phase of matter with no equilibrium counterpart. We include a compendium of the necessary background on the statistical mechanics of phase structure in many- body systems, before specializing to a detailed discussion of the nature, and diagnostics, of TTSB. In particular, we provide precise definitions that formalize the notion of a time-crystal as a stable, macroscopic, conservative clock — explaining both the need for a many-body system in the infinite volume limit, and for a lack of net energy absorption or dissipation. Our discussion emphasizes that TTSB in a time-crystal is accompanied by the breaking of a spatial symmetry — so that time-crystals exhibit a novel form of spatiotemporal order. -
Conclusion: the Impact of Statistical Physics
Conclusion: The Impact of Statistical Physics Applications of Statistical Physics The different examples which we have treated in the present book have shown the role played by statistical mechanics in other branches of physics: as a theory of matter in its various forms it serves as a bridge between macroscopic physics, which is more descriptive and experimental, and microscopic physics, which aims at finding the principles on which our understanding of Nature is based. This bridge can be crossed fruitfully in both directions, to explain or predict macroscopic properties from our knowledge of microphysics, and inversely to consolidate the microscopic principles by exploring their more or less distant macroscopic consequences which may be checked experimentally. The use of statistical methods for deductive purposes becomes unavoidable as soon as the systems or the effects studied are no longer elementary. Statistical physics is a tool of common use in the other natural sciences. Astrophysics resorts to it for describing the various forms of matter existing in the Universe where densities are either too high or too low, and tempera tures too high, to enable us to carry out the appropriate laboratory studies. Chemical kinetics as well as chemical equilibria depend in an essential way on it. We have also seen that this makes it possible to calculate the mechan ical properties of fluids or of solids; these properties are postulated in the mechanics of continuous media. Even biophysics has recourse to it when it treats general properties or poorly organized systems. If we turn to the domain of practical applications it is clear that the technology of materials, a science aiming to develop substances which have definite mechanical (metallurgy, plastics, lubricants), chemical (corrosion), thermal (conduction or insulation), electrical (resistance, superconductivity), or optical (display by liquid crystals) properties, has a great interest in statis tical physics. -
Influence of Thermal Fluctuations on Active Diffusion at Large Péclet Numbers
Influence of thermal fluctuations on active diffusion at large Péclet numbers Cite as: Phys. Fluids 33, 051904 (2021); https://doi.org/10.1063/5.0049386 Submitted: 04 March 2021 . Accepted: 15 April 2021 . Published Online: 14 May 2021 O. T. Dyer, and R. C. Ball COLLECTIONS This paper was selected as Featured ARTICLES YOU MAY BE INTERESTED IN Numerical and theoretical modeling of droplet impact on spherical surfaces Physics of Fluids 33, 052112 (2021); https://doi.org/10.1063/5.0047024 Phase-field modeling of selective laser brazing of diamond grits Physics of Fluids 33, 052113 (2021); https://doi.org/10.1063/5.0049096 Collective locomotion of two uncoordinated undulatory self-propelled foils Physics of Fluids 33, 011904 (2021); https://doi.org/10.1063/5.0036231 Phys. Fluids 33, 051904 (2021); https://doi.org/10.1063/5.0049386 33, 051904 © 2021 Author(s). Physics of Fluids ARTICLE scitation.org/journal/phf Influence of thermal fluctuations on active diffusion at large Peclet numbers Cite as: Phys. Fluids 33, 051904 (2021); doi: 10.1063/5.0049386 Submitted: 4 March 2021 . Accepted: 15 April 2021 . Published Online: 14 May 2021 O. T. Dyera) and R. C. Ball AFFILIATIONS Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom a)Author to whom correspondence should be addressed: [email protected] ABSTRACT Three-dimensional Wavelet Monte Carlo dynamics simulations are used to study the dynamics of passive particles in the presence of microswimmers—both represented by neutrally buoyant spheres—taking into account the often-omitted thermal motion alongside the hydrody- namic flows generated by the swimmers. -
Research Statement Statistical Physics Methods and Large Scale
Research Statement Maxim Shkarayev Statistical physics methods and large scale computations In recent years, the methods of statistical physics have found applications in many seemingly un- related areas, such as in information technology and bio-physics. The core of my recent research is largely based on developing and utilizing these methods in the novel areas of applied mathemat- ics: evaluation of error statistics in communication systems and dynamics of neuronal networks. During the coarse of my work I have shown that the distribution of the error rates in the fiber op- tical communication systems has broad tails; I have also shown that the architectural connectivity of the neuronal networks implies the functional connectivity of the afore mentioned networks. In my work I have successfully developed and applied methods based on optimal fluctuation theory, mean-field theory, asymptotic analysis. These methods can be used in investigations of related areas. Optical Communication Systems Error Rate Statistics in Fiber Optical Communication Links. During my studies in the Ap- plied Mathematics Program at the University of Arizona, my research was focused on the analyti- cal, numerical and experimental study of the statistics of rare events. In many cases the event that has the greatest impact is of extremely small likelihood. For example, large magnitude earthquakes are not at all frequent, yet their impact is so dramatic that understanding the likelihood of their oc- currence is of great practical value. Studying the statistical properties of rare events is nontrivial because these events are infrequent and there is rarely sufficient time to observe the event enough times to assess any information about its statistics. -
Statistical Physics II
Statistical Physics II. Janos Polonyi Strasbourg University (Dated: May 9, 2019) Contents I. Equilibrium ensembles 3 A. Closed systems 3 B. Randomness and macroscopic physics 5 C. Heat exchange 6 D. Information 8 E. Correlations and informations 11 F. Maximal entropy principle 12 G. Ensembles 13 H. Second law of thermodynamics 16 I. What is entropy after all? 18 J. Grand canonical ensemble, quantum case 19 K. Noninteracting particles 20 II. Perturbation expansion 22 A. Exchange correlations for free particles 23 B. Interacting classical systems 27 C. Interacting quantum systems 29 III. Phase transitions 30 A. Thermodynamics 32 B. Spontaneous symmetry breaking and order parameter 33 C. Singularities of the partition function 35 IV. Spin models on lattice 37 A. Effective theories 37 B. Spin models 38 C. Ising model in one dimension 39 D. High temperature expansion for the Ising model 41 E. Ordered phase in the Ising model in two dimension dimensions 41 V. Critical phenomena 43 A. Correlation length 44 B. Scaling laws 45 C. Scaling laws from the correlation function 47 D. Landau-Ginzburg double expansion 49 E. Mean field solution 50 F. Fluctuations and the critical point 55 VI. Bose systems 56 A. Noninteracting bosons 56 B. Phases of Helium 58 C. He II 59 D. Energy damping in super-fluid 60 E. Vortices 61 VII. Nonequillibrium processes 62 A. Stochastic processes 62 B. Markov process 63 2 C. Markov chain 64 D. Master equation 65 E. Equilibrium 66 VIII. Brownian motion 66 A. Diffusion equation 66 B. Fokker-Planck equation 68 IX. Linear response 72 A. -
Chapter 7 Equilibrium Statistical Physics
Chapter 7 Equilibrium statistical physics 7.1 Introduction The movement and the internal excitation states of atoms and molecules constitute the microscopic basis of thermodynamics. It is the task of statistical physics to connect the microscopic theory, viz the classical and quantum mechanical equations of motion, with the macroscopic laws of thermodynamics. Thermodynamic limit The number of particles in a macroscopic system is of the order of the Avogadro constantN 6 10 23 and hence huge. An exact solution of 1023 coupled a ∼ · equations of motion will hence not be possible, neither analytically,∗ nor numerically.† In statistical physics we will be dealing therefore with probability distribution functions describing averaged quantities and theirfluctuations. Intensive quantities like the free energy per volume,F/V will then have a well defined thermodynamic limit F lim . (7.1) N →∞ V The existence of a well defined thermodynamic limit (7.1) rests on the law of large num- bers, which implies thatfluctuations scale as 1/ √N. The statistics of intensive quantities reduce hence to an evaluation of their mean forN . →∞ Branches of statistical physics. We can distinguish the following branches of statistical physics. Classical statistical physics. The microscopic equations of motion of the particles are • given by classical mechanics. Classical statistical physics is incomplete in the sense that additional assumptions are needed for a rigorous derivation of thermodynamics. Quantum statistical physics. The microscopic equations of quantum mechanics pro- • vide the complete and self-contained basis of statistical physics once the statistical ensemble is defined. ∗ In classical mechanics one can solve only the two-body problem analytically, the Kepler problem, but not the problem of three or more interacting celestial bodies. -
Introduction to Two-Dimensional Conformal Field Theory
Introduction to two-dimensional conformal field theory Sylvain Ribault CEA Saclay, Institut de Physique Th´eorique [email protected] February 5, 2019 Abstract We introduce conformal field theory in two dimensions, from the basic principles to some of the simplest models. From the representations of the Virasoro algebra on the one hand, and the state-field correspondence on the other hand, we deduce Ward identities and Belavin{Polyakov{Zamolodchikov equations for correlation functions. We then explain the principles of the conformal bootstrap method, and introduce conformal blocks. This allows us to define and solve minimal models and Liouville theory. We also introduce the free boson with its abelian affine Lie algebra. Lecture notes for the \Young Researchers Integrability School", Wien 2019, based on the earlier lecture notes [1]. Estimated length: 7 lectures of 45 minutes each. Material that may be skipped in the lectures is in green boxes. Exercises are in green boxes when their statements are not part of the lectures' text; this does not make them less interesting as exercises. 1 Contents 0 Introduction2 1 The Virasoro algebra and its representations3 1.1 Algebra.....................................3 1.2 Representations.................................4 1.3 Null vectors and degenerate representations.................5 2 Conformal field theory6 2.1 Fields......................................6 2.2 Correlation functions and Ward identities...................8 2.3 Belavin{Polyakov{Zamolodchikov equations................. 10 2.4 Free boson.................................... 10 3 Conformal bootstrap 12 3.1 Single-valuedness................................ 12 3.2 Operator product expansion and crossing symmetry............. 13 3.3 Degenerate fields and the fusion product................... 16 4 Minimal models 17 4.1 Diagonal minimal models...........................