DOCSLIB.ORG

Topological Floquet States, Artificial Gauge Fields in Strongly Correlated Quantum Fluids Kirill Plekhanov

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Topological Floquet States, Artificial Gauge Fields in Strongly Correlated Quantum Fluids Kirill Plekhanov Topological Floquet states, artificial gauge fields in strongly correlated quantum fluids Kirill Plekhanov To cite this version: Kirill Plekhanov. Topological Floquet states, artificial gauge fields in strongly correlated quantum fluids. Condensed Matter [cond-mat]. Université Paris-Saclay, 2018. English. NNT : 2018SACLS264. tel-01874629 HAL Id: tel-01874629 https://tel.archives-ouvertes.fr/tel-01874629 Submitted on 14 Sep 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Topological Floquet states, artificial gauge fields in strongly correlated quantum fluids NNT: 2018SACLS264 Thèse de doctorat de l’Université Paris-Saclay préparée à l’Université Paris-Sud, Laboratoire de Physique Théorique et Modèles Statistiques et l’Ecole Polytechnique, Centre de Physique Théorique École doctorale n◦ 564 Physique en Île-de-France Spécialité de doctorat: Physique Thèse présentée et soutenue à Orsay, le 7 septembre 2018, par M. Kirill Plekhanov Composition du Jury: M. Nicolas Regnault Président du Jury Professeur — École Normale Supérieure, Laboratoire Pierre Aigrain M. Nathan Goldman Rapporteur Professeur — Université libre de Bruxelles, Physics of Complex Systems (CENOLI) M. Titus Neupert Rapporteur Professeur Associé — Universität Zürich, Institut für Theoretische Physik M. Mark Oliver Goerbig Examinateur Directeur de Recherche — Université Paris-Sud, Laboratoire de Physique des Solides M. Walter Hofstetter Examinateur Professeur — Goethe-Universität Frankfurt, Institut für Theoretische Physik M. Guido Pupillo Examinateur Professeur — Université de Strasbourg, Institut de Science et d’Ingénierie Supramoléculaires Mme Karyn Le Hur Directrice de thèse Directrice de Recherche — Ecole Polytechnique, Centre de Physique Théorique M. Guillaume Roux Directeur de thèse Maître de Conférences — Université Paris-Sud, Laboratoire de Physique Théorique et Modèles Statistiques Thèse de doctorat ii – What’re quantum mechanics? – I don’t know. People who repair quantums, I suppose. Terry Pratchett iii Acknowledgements First and foremost, I would like to thank my thesis supervisors: Guillaume Roux and Karyn Le Hur. During these three years I had a great opportunity to learn from them and work on extremely interesting projects. Our numerous discussions were crucial for forming my current worldview, and I am proud to be their student. I am also very grateful to the reviewers of my thesis Nathan Goldman and Titus Neupert, as well as the Jury members Mark Oliver Goerbig, Walter Hofstetter, Guido Pupillo, and Nicolas Regnault. I am thankful that they had time to attend my PhD defense, read very carefully the manuscript to evaluate my work and participate in our mini-workshop. I appreciated very much the question session that followed the defense, the discussions, and the talks of the mini-workshop. During my PhD I had an opportunity to visit several other laboratories and dis- cuss about the physics with brilliant scientists. Such discussions were enlightening to me and allowed to see what other people are interested in, learn new techniques and explore different approaches of doing science. In this context, I would like to particularly thank Ivana Vasic and Walter Hofstetter for taking part in a challenging yet enjoyable collaborative project we worked on together. I also appreciated very much the discussions with Hans Peter Buchler, Piers Coleman, Antoine Georges, Steven Girvin, Leonid Glazman, Jelena Klinovaja, Daniel Loss and Lode Pollet, as well as during my visit of the Stewart Blusson Quantum Matter Institute, on the CI- FAR conferences, and FOR 2414 DFG meetings. Finally, I am very grateful to Eugene Bogomolny and Gregoire Misguich for playing a crucial role in my PhD and follow- ing my progress as a parrain and a tutor. My PhD time was shared between two laboratories: the LPTMS and the CPHT. I would like to thank very much their directors: Emanuel Trizac, Jean-René Chazottes and Bernard Pire, and the administrative teams. Without their help this thesis would simply be impossible. I am also very proud to be a part of the student/postdoc equipes at LPTMS and CPHT. It was a pleasure to meet such wonderful people, share the same offices (yes, there are two of them), go for a lunch and enjoy the tea/coffee time (and not only) together. I am happy that I could spend a significant part of these three years with Aurelien, Ariane, Ines, Loïc Z. and Tal. Unfortunately, there was lesser time I could spend with you, Alex, Aleksey, Bertrand, Fan, Ivan, Loïc H., Luca, Matthieu, Nina, Samuel, Thibault B. and Thibault G., and with my friends outside of the labs: Camille, Félix, Marc, Marie, Paul, Shuwei and Thibault L.. But still I am glad that you were there. Finally, my greatest thanks go to my parents for encouraging and supporting me. v Contents Acknowledgements iii Introduction1 1 Condensed matter in the age of topological phase transitions5 1.1 New look at the phase transitions......................6 1.1.1 Ginzburg-Landau paradigm of phase transitions.........6 1.1.2 Beyond Ginzburg-Landau theory..................7 1.2 Conventional band theory.......................... 10 1.2.1 Block-diagonalization in the momentum space.......... 10 1.2.2 Bogoliubov transformations..................... 12 A. Fermions.............................. 12 B. Bosons................................ 12 1.2.3 Interactions and approximations. BCS theory example..... 13 1.3 Few words about topology.......................... 14 1.3.1 A coffee cup or a doughnut?.................... 14 1.3.2 Relevant definitions......................... 15 A. Basics of topological spaces and manifolds.......... 15 B. Covectors, tensors and differential forms............ 17 C. Parallel transport: connection and curvature......... 18 D. Topological invariants...................... 20 1.3.3 Homotopy and cohomology.................... 21 A. Homotopy groups......................... 21 B. De Rham cohomology groups.................. 22 1.3.4 Basics of fibre bundles........................ 23 A. Fibre bundles in geometry and in physics........... 23 B. Connection and curvature in fibre bundles........... 25 C. Topology of fibre bundles.................... 27 1.4 Topological band theory........................... 29 1.4.1 Berry’s connection and Berry’s phase............... 29 A. Adiabatic evolution argument.................. 29 B. Zak phase.............................. 32 1.4.2 Berry’s curvature and the first Chern number.......... 33 A. Definitions............................. 33 B. Many sides of the first Chern number through the examples 34 1.4.3 Topological phase transitions.................... 36 1.4.4 Symmetry protected topological states............... 38 1.4.5 Bulk-boundary correspondence................... 40 1.5 Role of topology in strongly correlated quantum systems........ 41 1.5.1 Fractional quantum Hall states................... 42 A. Laughlin states.......................... 42 B. Generalizations.......................... 43 1.5.2 Interacting SPT states and intrinsic topological order...... 45 vi 1.5.3 Frustrated quantum magnetism and spin liquids........ 46 2 Chiral phases of the Haldane Chern insulator 49 2.1 Dirac materials and Chern insulators.................... 50 2.1.1 Graphene as a Dirac material.................... 51 2.1.2 Haldane model as a Chern insulator................ 53 A. Opening a gap at Dirac points.................. 53 B. Topological phase transition................... 54 2.1.3 Anisotropy and generalizations of the Haldane model..... 57 2.2 Anisotropic Haldane model for bosons with interactions........ 57 2.2.1 Overview of the problem...................... 59 2.2.2 Superfluid phases........................... 60 A. Zero-momentum phase...................... 60 B. Critical value of NNN hopping amplitude........... 62 C. Finite-momentum phase..................... 64 D. Interaction effects......................... 67 2.2.3 Excitation properties......................... 69 2.2.4 Mott insulator phase......................... 70 2.3 Interacting bosons on brickwall ladder geometry............. 72 2.3.1 Band structure in free case...................... 73 2.3.2 Interactions and bosonization.................... 74 A. Strong t1 phase.......................... 76 B. Strong t2 phase........................... 77 2.3.3 Perspectives.............................. 78 3 Phases of the bosonic Kane-Mele Hubbard model 81 3.1 Kane-Mele model and topological insulators............... 82 3.1.1 Introduction to the model and symmetries............ 83 3.1.2 Z2 topological invariant....................... 85 3.1.3 Interactions in the Kane-Mele model................ 87 3.2 Bosonic Kane-Mele-Hubbard model.................... 88 3.2.1 Overview of the problem...................... 89 3.2.2 Mott – superfluid phase transitions................ 90 3.2.3 Mott phase and emergent magnetism............... 91 3.3 Effective frustrated spin-1/2 XY model.................. 93 3.3.1 Classical phase diagram....................... 94 3.3.2 Magnetically ordered states..................... 95 A. Fidelity metric........................... 96 B.
Load more

Recommended publications
  • Momentum-Dependent Mass and AC Hall Conductivity of Quantum Anomalous Hall Insulators and Their Relation to the Parity Anomaly
    PHYSICAL REVIEW RESEARCH 2, 033193 (2020) Momentum-dependent mass and AC Hall conductivity of quantum anomalous Hall insulators and their relation to the parity anomaly Christian Tutschku, Jan Böttcher , René Meyer, and E. M. Hankiewicz* Institute for Theoretical Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, Julius-Maximilians-Universität Würzburg, 97074 Würzburg, Germany (Received 9 March 2020; accepted 15 July 2020; published 4 August 2020) The Dirac mass of a two-dimensional QAH insulator is directly related to the parity anomaly of planar quantum electrodynamics, as shown initially by Niemi and Semenoff [Phys. Rev. Lett. 51, 2077 (1983)]. In this work, we connect the additional momentum-dependent Newtonian mass term of a QAH insulator to the parity anomaly. We reveal that in the calculation of the effective action, before renormalization, the Newtonian mass acts similar to a parity-breaking element of a high-energy regularization scheme. This calculation allows us to derive the finite frequency correction to the DC Hall conductivity of a QAH insulator. We predict that the leading order AC correction contains a term proportional to the Chern number. This term originates from the Newtonian mass and can be measured via electrical or magneto-optical experiments. Moreover, we prove that the Newtonian mass significantly changes the resonance structure of the AC Hall conductivity in comparison to pure Dirac systems like graphene. DOI: 10.1103/PhysRevResearch.2.033193 I. INTRODUCTION While the contribution of the Dirac mass to the effective ac- tion of a QED + systems was initially shown in Refs. [22,23], The discovery of Dirac materials, such as topological 2 1 the effective action of Chern insulator in the presence of a insulators [1–10] and Weyl or Dirac [11–16] semimetals Newtonian mass has not yet been analyzed.
    [Show full text]
  • Parity Anomaly and Duality
    Parity Anomaly and Duality Web Chen-Te Ma 1 Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei 10617, Taiwan, R.O.C. Abstract We review the parity anomaly and a duality web in 2+1 dimensions. An odd di- mensional non-interacting Dirac fermion theory is not parity invariant at quantum level. We demonstrate the parity anomaly in a three dimensional non-interacting Dirac fermion theory and a one dimensional non-interacting Dirac fermion theory. These theories can generate non-gauge invariant Abelian Chern-Simons terms at a finite temperature through an effective action. The parity anomaly also leads us to study the duality web in 2+1 dimensions, in which the 2+1 dimensional duality web begins from the conjecture of a duality between a three dimensional Dirac fermion theory and a three dimensional interacting scalar field theory at the Wilson-Fisher arXiv:1802.08959v3 [hep-th] 2 Jul 2018 fixed point. We first review the duality web for the flat background, then we discuss its extension to the spinc manifold to avoid inconsistency from the spin structure. This also leads a global effect. We discuss that the composite fermions approach of the quantum Hall system also suffers from the same issue of the global description. Finally, we use perspective of the electric-magnetic duality of the Abelian gauge theory in 3+1 dimensions to study the 2+1 dimensional duality web. 1e-mail address: [email protected] 1 Introduction Symmetry can be seen as an operation that maps an object to itself. The symmetry can be built from a mathematical group.
    [Show full text]
  • Symmetries, Anomalies and Duality in Chern-Simons Matter Theories
    Symmetries, Anomalies and Duality in Chern-Simons Matter Theories Po-Shen Hsin A Dissertation Presented to the Faculty of Princeton University in Candidacy for the Degree of Doctor of Philosophy Recommended for Acceptance by the Department of Physics Adviser: Nathan Seiberg September 2018 c Copyright by Po-Shen Hsin, 2018. All rights reserved. Abstract This thesis investigates the properties of quantum field theory with Chern-Simons interac- tion in three spacetime dimension. We focus on their symmetries and anomalies. We find many theories exhibit the phenomenon of duality - different field theories describe the same long-distance physics, and we will explore its consequence. We start by discussing Chern-Simons matter dualities with unitary gauge groups. The theories can couple to background gauge field for the global U(1) symmetry, and we produce new dualities by promoting the fields to be dynamical. We then continue to discuss theories with orthogonal and symplectic gauge groups and their dualities. For the orthogonal gauge algebra there can be discrete levels in addition to the ordinary Chern-Simons term, and the dualities require specific discrete levels as well as precise global forms of the gauge groups. We present several consistency tests for the dualities, such as consistency under deformation by the mass terms on both sides of the duality. When the matter fields are heavy the dualities reduce at long distance to the level-rank dualities between Chern-Simons theories, which we prove rigorously. We clarify the global form of the gauge groups, and we show the level-rank dualities hold generally only between spin topological quantum field theories.
    [Show full text]
  • Gauge Theory
    Preprint typeset in JHEP style - HYPER VERSION 2018 Gauge Theory David Tong Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, Wilberforce Road, Cambridge, CB3 OBA, UK http://www.damtp.cam.ac.uk/user/tong/gaugetheory.html [email protected] Contents 0. Introduction 1 1. Topics in Electromagnetism 3 1.1 Magnetic Monopoles 3 1.1.1 Dirac Quantisation 4 1.1.2 A Patchwork of Gauge Fields 6 1.1.3 Monopoles and Angular Momentum 8 1.2 The Theta Term 10 1.2.1 The Topological Insulator 11 1.2.2 A Mirage Monopole 14 1.2.3 The Witten Effect 16 1.2.4 Why θ is Periodic 18 1.2.5 Parity, Time-Reversal and θ = π 21 1.3 Further Reading 22 2. Yang-Mills Theory 26 2.1 Introducing Yang-Mills 26 2.1.1 The Action 29 2.1.2 Gauge Symmetry 31 2.1.3 Wilson Lines and Wilson Loops 33 2.2 The Theta Term 38 2.2.1 Canonical Quantisation of Yang-Mills 40 2.2.2 The Wavefunction and the Chern-Simons Functional 42 2.2.3 Analogies From Quantum Mechanics 47 2.3 Instantons 51 2.3.1 The Self-Dual Yang-Mills Equations 52 2.3.2 Tunnelling: Another Quantum Mechanics Analogy 56 2.3.3 Instanton Contributions to the Path Integral 58 2.4 The Flow to Strong Coupling 61 2.4.1 Anti-Screening and Paramagnetism 65 2.4.2 Computing the Beta Function 67 2.5 Electric Probes 74 2.5.1 Coulomb vs Confining 74 2.5.2 An Analogy: Flux Lines in a Superconductor 78 { 1 { 2.5.3 Wilson Loops Revisited 85 2.6 Magnetic Probes 88 2.6.1 't Hooft Lines 89 2.6.2 SU(N) vs SU(N)=ZN 92 2.6.3 What is the Gauge Group of the Standard Model? 97 2.7 Dynamical Matter 99 2.7.1 The Beta Function Revisited 100 2.7.2 The Infra-Red Phases of QCD-like Theories 102 2.7.3 The Higgs vs Confining Phase 105 2.8 't Hooft-Polyakov Monopoles 109 2.8.1 Monopole Solutions 112 2.8.2 The Witten Effect Again 114 2.9 Further Reading 115 3.
    [Show full text]
  • Masaki Oshikawa (ISSP, Utokyo) 1 Lecture 1: Anomaly and Condensed Matter Physics
    Symmetry-protected critical phases and global anomaly Croucher Advanced Institute “Topology in Condensed Matter and High-Energy Physics” January 3-5, 2018 @ Chinese University of Hong Kong Masaki Oshikawa (ISSP, UTokyo) 1 Lecture 1: Anomaly and Condensed Matter Physics Lecture II: Symmetry-Protected Critical Phases and Global Anomaly 2 Dirac Fermion massless (m=0) “Dirac cone” 3 Axial Symmetry and Current Massless Dirac fermion Lagrangian density = ¯iγµ@ L µ “vector” U(1) symmetry ⇒ charge current conservation i✓ µ e V @µj =0 ! i✓ µ µ ¯ e− V ¯ j = ¯ ! 2 γµ, γ5 =0 γ5 =1 in even space-time dimensions { } “axial” U(1) symmetry if m=0 ⇒ axial current conservation ei✓A @µj5 =0 ! µ i✓ 5 5 ¯ e A ¯ j = ¯µγ ! µ 4 U(1) Chiral Anomaly Noether’s theorem (“classical”): Massless Dirac fermion ⇒ two conserved currents However, one of these conservation laws is inevitably broken in quantum theory through “regularization” of UV divergence = ¯iγµ(@ iA ) Adler/Bell-Jackiw (1969) L µ − µ Anomalous non-conservation of axial current! µ 5 γ γ 1 @µj5 = ✏ F µ⌫ F ⇢ µ 16⇡2 µ⌫⇢σ Decay of neutral pion ⇡0 γγ (in 3+1 dimensions) 5 ! Regularization/Renormalization “renormalization theory is simply a way to sweep the difficulties of the divergences of electrodynamics under the rug.” Richard Feynman, in Nobel Lecture (1965) 6 Modern Understanding of Renormalization Field theory = universal long-distance behavior of lattice model / condensed matter systems Exact symmetry in the lattice model remains exact in the long-distance limit → no anomaly? Kenneth G. Wilson How can we understand anomaly (1936-2013) in this context? 7 Chiral Anomaly in 1+1 Dim.
    [Show full text]
  • Extended Quantum Field Theory, Index Theory, and the Parity Anomaly
    Heriot-Watt University Research Gateway Extended Quantum Field Theory, Index Theory, and the Parity Anomaly Citation for published version: Müller, L & Szabo, RJ 2018, 'Extended Quantum Field Theory, Index Theory, and the Parity Anomaly', Communications in Mathematical Physics, vol. 362, no. 3, pp. 1049-1109. https://doi.org/10.1007/s00220- 018-3169-x Digital Object Identifier (DOI): 10.1007/s00220-018-3169-x Link: Link to publication record in Heriot-Watt Research Portal Document Version: Peer reviewed version Published In: Communications in Mathematical Physics Publisher Rights Statement: This is a post-peer-review, pre-copyedit version of an article published in Communications in Mathematical Physics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s00220-018-3169-x General rights Copyright for the publications made accessible via Heriot-Watt Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy Heriot-Watt University has made every reasonable effort to ensure that the content in Heriot-Watt Research Portal complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 23. Sep. 2021 EMPG{17{09 Extended quantum field theory, index theory and the parity anomaly Lukas M¨uller and Richard J. Szabo Department of Mathematics Heriot-Watt University Colin Maclaurin Building, Riccarton, Edinburgh EH14 4AS, U.K.
    [Show full text]
  • Modified Instanton Sum in QCD and Higher-Groups
    Prepared for submission to JHEP Modified instanton sum in QCD and higher-groups Yuya Tanizaki, Mithat Ünsal North Carlina State University, Raleigh, NC, 27607, USA E-mail: [email protected], [email protected] Abstract: We consider the SU(N) Yang-Mills theory, whose topological sectors are restricted to the instanton number with integer multiples of p. We can formulate such a quantum field theory maintaining locality and unitarity, and the model contains both 2π- periodic scalar and 3-form gauge fields. This can be interpreted as coupling a topological theory to Yang-Mills theory, so the local dynamics becomes identical with that of pure Yang- Mills theory. The theory has not only ZN 1-form symmetry but also Zp 3-form symmetry, and we study the global nature of this theory from the recent ’t Hooft anomaly matching. The computation of ’t Hooft anomaly incorporates an intriguing higher-group structure. We also carefully examine that how such kinematical constraint is realized in the dynamics 3 1 by using the large-N and also the reliable semiclassics on R S , and we find that the × topological susceptibility plays a role of the order parameter for the Zp 3-form symmetry. Introducing a fermion in the fundamental or adjoint representation, we find that the chiral symmetry becomes larger than the usual case by Zp, and it leads to the extra p vacua by discrete chiral symmetry breaking. No dynamical domain wall can interpolate those extra vacua since such objects must be charged under the 3-form symmetry in order to match the ’t Hooft anomaly.
    [Show full text]
  • Five-Dimensional Scfts and Gauge Theory Phases: an M-Theory/Type IIA Perspective
    YITP-SB-18-41 Five-dimensional SCFTs and gauge theory phases: an M-theory/type IIA perspective Cyril Closset,[ Michele Del Zotto,] Vivek Saxena\ [Mathematical Institute, University of Oxford Woodstock Road, Oxford, OX2 6GG, United Kingdom ]Department of Mathematical Sciences and Centre for Particle Theory Durham University, Durham DH1 3LE, UK \C.N. Yang Institute for Theoretical Physics, Stony Brook University Stony Brook, NY 11794-3840, USA Abstract: We revisit the correspondence between Calabi-Yau (CY) threefold isolated singularities X and five-dimensional superconformal field theories (SCFTs), which arise at low energy in M-theory on the space-time transverse to X. Focussing on the case of toric CY singularities, we analyze the \gauge-theory phases" of the SCFT by exploiting fiberwise M-theory/type IIA duality. In this setup, the low-energy gauge group simply arises on stacks of coincident D6-branes wrapping 2-cycles in some ALE space of type AM−1 fibered over a real line, and the map between the K¨ahlerparameters of X and the Coulomb branch parameters of the field theory (masses and VEVs) can be read off systematically. Different type IIA \reductions" give rise to different gauge theory phases, whose existence depends on the particular (partial) resolutions of the isolated singularity X. We also comment on the case of non-isolated toric singularities. Inciden- arXiv:1812.10451v3 [hep-th] 17 Apr 2019 tally, we propose a slightly modified expression for the Coulomb-branch prepotential of 5d N = 1 gauge theories. Keywords: Superconformal theories
    [Show full text]
  • Anomalies and Bosonization Arxiv:1810.04414V3 [Cond-Mat.Str-El]
    Anomalies and Bosonization Ryan Thorngren Department of Condensed Matter Physics, Weizmann Institute of Science Department of Mathematics, University of California, Berkeley July 18, 2019 Abstract Recently, general methods of bosonization beyond 1+1 dimensions have been devel- oped. In this article, we review these bosonizations and extend them to systems with boundary. Of particular interest is the case when the bulk theory is a G-symmetry protected topological phase and the boundary theory has a G 't Hooft anomaly. We discuss how, when the anomaly is not realizable in a bosonic system, the G symmetry algebra becomes modified in the bosonization of the anomalous theory. This gives us a useful tool for understanding anomalies of fermionic systems, since there is no way to compute a boundary gauge variation of the anomaly polynomial, as one does for anomalies of bosonic systems. We take the chiral anomalies in 1+1D as case studies and comment on our expectations for parity/time reversal anomalies in 2+1D. We also provide a derivation of new constraints in SPT phases with domain defects decorated by p + ip superconductors and Kitaev strings, which is necessary to understand the bosonized symmetry algebras which appear. 1 Introduction A theory is said to have an 't Hooft anomaly if it has a global symmetry G which cannot be gauged while preserving locality of interactions. Anomalies are quantized, so if we can identify an anomaly at weak coupling, it is guaranteed to hold at all energy scales [1]. This makes anomalies useful for constraining phase diagrams of condensed matter systems whose long range limit is strongly interacting.
    [Show full text]
  • Jhep07(2019)018
    Published for SISSA by Springer Received: May 21, 2019 Revised: June 20, 2019 Accepted: June 26, 2019 Published: July 3, 2019 Fractional θ angle, 't Hooft anomaly, and quantum instantons in charge-q multi-flavor Schwinger model JHEP07(2019)018 Tatsuhiro Misumi,a;b;c Yuya Tanizakid and Mithat Unsal¨ d aDepartment of Mathematical Science, Akita University, Akita 010-8502, Japan biTHEMS Program, RIKEN, Wako 351-0198, Japan cResearch and Education Center for Natural Sciences, Keio University, Kanagawa 223-8521, Japan dDepartment of Physics, North Carolina State University, Raleigh, NC 27607, U.S.A. E-mail: [email protected], [email protected], [email protected] Abstract: This work examines non-perturbative dynamics of a 2-dimensional QFT by using discrete 't Hooft anomaly, semi-classics with circle compactification and bosonization. We focus on charge-q N-flavor Schwinger model, and also Wess-Zumino-Witten model. We first apply the recent developments of discrete 't Hooft anomaly matching to theories on R2 and its compactification to R S1 . We then compare the 't Hooft anomaly with × L dynamics of the models by explicitly constructing eigenstates and calculating physical quantities on the cylinder spacetime with periodic and flavor-twisted boundary conditions. We find different boundary conditions realize different anomalies. Especially under the twisted boundary conditions, there are Nq vacua associated with discrete chiral symmetry breaking. Chiral condensates for this case have fractional θ dependence eiθ=Nq, which provides the Nq-branch structure with soft fermion mass. We show that these behaviors at a small circumference cannot be explained by usual instantons but should be understood by \quantum" instantons, which saturate the BPS bound between classical action and quantum-induced effective potential.
    [Show full text]
  • Parity Anomaly in Even Dimensions
    Parity anomaly in even dimensions Dmitri Vassilevich UFABC VI Conference "Models in Quantum Field Theory", 30.08.2018 Dmitri Vassilevich Parity anomaly Contents Overview and history Induced Chern-Simons current on the boundary Topologically non-trivial bundles Some further developments Based on works with Maxim Kurkov, PRD 2017, JHEP 2018 Support: CNPq, FAPESP Dmitri Vassilevich Parity anomaly Consider one generation of Dirac fermions in odd d. Niemi & Semenoff, Redlich, Alwarez-Gaume et al, Deser et al, Fosco et al: – gauge invariant renormalization violates the parity symmetry. – spectral asymmetry of the Dirac operator leads to the Parity anomaly in the one-loop effective action. That reads (for d = 3, m = 0, abelian gauge field) ik Z p W odd(A) = d3x habc A @ A ; k = ± 1 4π a b c 2 which is the Chern-Simons action of the level k. Dmitri Vassilevich Parity anomaly New reincarnation: Dirac/Weyl materials in the condensed matter physics (topological insulators, Weyl semimetals, etc.). Quasiparticles in these materials obey the Dirac equation that predicts topologically protected surface modes that are in turn described by the Dirac operator in 3D. The problem: does the surface mode generate the half-integer Hall conductivity? Purpose of this work: compute the parity anomaly directly on a 4D manifold with boundary. Dmitri Vassilevich Parity anomaly The setup Consider the Dirac operator with an abelian gauge field µ D= = iγ (rµ + iAµ) on a 4D flat Euclidean manifold M with a boundary S @M = α @Mα consisting of several connected components @Mα. Bag boundary conditions Define the projectors 1 5 n Π± := 2 1 ± i"αγ γ "α = ±1.
    [Show full text]
  • Anomalies in Quantum Field Theory
    20 Anomalies in Quantum Field Theory 20.1 The chiral anomaly In classical field theory, discussed in chapter 3, we learn that symmetries dic- tate the existence of conservation laws. At the quantum level, conservation laws of continuous symmetries are embodied by Ward identities which dic- tate the behavior of correlation functions. However we will now see that in quantum field theory there are many instances of symmetries oftheclassical theory that do not survive at the quantum level due to a quantum anomaly. Most examples of anomalies involve Dirac fermions that are massless at the level of the Lagrangian. Global and gauge symmetries of theories of Dirac fermions involve under- standing their currents which are products of Dirac operators at short dis- tances. Such operators require a consistent definition (and anormal-ordering prescription). Hence, some sort of regularization is neededforaproperdefi- nition. The problem is that all of the symmetries can simultaneously survive regularization. While in scalar field theories, at least in flat spacetimes, this is not a problem, it turns out to be a significant problem in theories with massless Dirac fermions, for which some formally conserved currents become anomalous. In the path integral language, a symmetry is anomalous if the action is invariant under the symmetry but the measure of the path integral is not. In this sense, quantum anomalies often arise in the process ofregularization of a quantum field theory. We will see, however, that they are closely related to topological considerations as well. The subject of anomalies in quantum field theory is discussed in many excellent textbooks, e.g.
    [Show full text]