Carlo Barenghi, Newcastle University
Russell Donnelly, University of Oregon
Quantum Turbulence
This hour will be devoted to a description of quantum turbulence,that is turbulence in superfluids. The first talk (~20 minutes) will be given by Russell Donnelly. He will describe briefly the problem of classical turbulence and how turbulence in superfluids is different. The second talk will be given by Carlo Barenghi who will discuss progress in the simulation of quantum turbulence which is capable of suggesting insights so far inaccessible to experiment.
Tomas Brauner, Vienna University of Technology
Nambu–Goldstone bosons: classification and effective actions
I will review the development in understanding Nambu–Goldstone bosons in quantum many-body systems. Particular emphasis will be put on two topics of my recent work: spontaneous breaking of spacetime symmetries and construction of topological effective Lagrangians.
J.C. Seamus Davis, Cornell University
Visualizing Quantum Matter
Recently developed techniques allow imaging of electronic quantum matter directly at the atomic scale. I will introduce the basic principles and describe the set of observables available from these techniques. As examples, I will survey visualization of exotic forms of electronic quantum matter including heavy fermions, quantum critical electrons, topological surface states, electronic liquid crystals, and high temperature superconductors.
Solomon Endlich, EFPL
Spontaneous symmetry breaking, gravity, and spinning objects
Space-time symmetries are a crucial ingredient of any theoretical model in physics. Unlike internal symmetries, which may or may not be gauged and/or spontaneously broken, space-time symmetries do not admit any ambiguity: they are gauged by gravity, and any conceivable physical system (other than the vacuum) is bound to break at least some of them. Motivated by this observation, I will sketch how to couple gravity with the Goldstone fields that non-linearly realize spontaneously broken space-time symmetries by weakly gauging the Poincare symmetry group in the context of the coset construction. To illustrate the power of this perspective I will build a low energy effective action that describes spinning objects coupled to gravity and describe its interpretation.
Liam Fitzpatrick, Stanford University
Wilsonian and Large N Approaches to Non-Fermi Liquids
We study the problem of metals near a quantum critical point using a local Wilsonian effective field theory of Fermi surface fermions coupled to massless boson (i.e. order parameter) fields, in particular in a large N limit where the boson is matrix-valued. We focus on regions of parameter space where the boson dresses the fermions into a non-Fermi liquid while the bosons are approximately controlled by the Wilson-Fisher fixed point.
Sean Hartnoll, Stanford University
Universal incoherent metallic transport
In an incoherent metal, transport is controlled by the collective diffusion of energy and charge rather than by quasiparticle or momentum relaxation. We explore the possibility of a universal bound D \gtrsim \hbar v_F^2 /(k_B T) on the underlying diffusion constants in an incoherent metal. Such a bound is loosely motivated by results from holographic duality, the uncertainty principle and from measurements of diffusion in strongly interacting non-metallic systems. Metals close to saturating this bound are shown to have a linear in temperature resistivity with an underlying dissipative timescale matching that recently deduced from experimental data on a wide range of metals. The phenomenology of universal incoherent transport is found to reproduce various further observations in strongly correlated metals, and motivates direct probes of diffusive processes and measurements of charge susceptibilities. We suggest that this bound may be responsible for the ubiquitous appearance of high temperature regimes in metals with T-linear resistivity.
Emanuel Katz, Boston University
Dynamical trapping near a quantum critical point
We consider a closed system where the parameter controlling a quantum phase transition is promoted to a dynamical field interacting with the quantum critical theory. In the case that the field has an energy extensive in the volume we can treat its evolution classically. We find that the field can become trapped near the phase transition point due to its interactions with the degrees of freedom of the quantum critical theory. The trapping/untrapping transition can be understood using Kibble-Zurek scaling arguments. We check the general framework numerically in the particular case of the 1D transverse field Ising chain, where the transverse magnetic field is dynamical. This constitutes a dynamical mechanism for tuning a relevant parameter to zero through a non-equilibrium process.
Zohar Komargodski, Weizmann Institute
Some Exact Results for Conformal Field Theories in d>2
John McGreevy, University of California, San Diego
Lattice models for anomalous field theories
Sergej Moroz, University of Washington
Effective field theory of two-dimensional nonrelativistic chiral superfluid
Due to the current search of Majorana fermions, the physics of two-dimensional identical fermions with short-range p-wave interactions is of considerable interest. My talk will be about the effective theory of a chiral p+ip fermionic superfluid at zero temperature. This theory naturally incorporates the parity and time reversal violating effects such as the Hall viscosity and the edge current. I will present some applications of this theory such as the linear response to external electromagnetic and gravitational fields and the density profile of an isolated vortex. Finally, the dual gauge reformulation of this theory will be presented.
Hitoshi Murayama, University of California, Berkeley
What's wrong with Goldstone?
Spontaneous Symmetry Breaking is a very universal concept applicable for a wide range of subjects: crystal, superfluid, neutron stars, Higgs boson, magnets, and many others. Yet there is a variety in the spectrum of gapless excitations even when the symmetry breaking patterns are the same. We unified all known examples in a single-line Lagrangian of the low-energy effective theory.
Riccardo Penco, Columbia University
Effective theories of vortex lines
Vortex lines are a distinctive feature of superfluids and are characterized by a very peculiar dynamics. In this talk, I will first discuss the behavior of vortex lines in a non-relativistic superfluids in the incompressible limit. I will then introduce an effective theory of vortex lines coupled to sound which applies to relativistic superfluids. I will conclude by briefly discussing the similarities between the effective theory for vortex lines and non-relativistic General Relativity.
Federico Piazza, University of Paris
Relativity of non relativistic systems
To the best of our knowledge, the fundamental laws of physics are Lorentz invariant. This means that condensed matter systems at finite density still display full Lorentz symmetry: it is just spontaneously broken (i.e. by state considered) and thus non-linearly realized. This simple observation allows to derive exact results about the spectrum of theories at finite charge density and suggests to classify condensed matter systems according to all the inequivalent ways in which boosts can be spontaneously broken.
Ira Rothstein, Carnegie Mellon University
Sudakov Form Factor and Von-Hove Singularities
In this talk I will discuss the analogies between high energy scattering of nucleons
and Fermi Liquid theory. In particular I will elucidate the relation between the
rapidity renormalization group utilized in such observables as transverse momentum
distribution and the effect of Von-Hove singularities on the low energy properties
of metals.
Subir Sachdev, Harvard University
Quantum matter without quasiparticles
Modern materials abound in systems to which the quasiparticle picture does not apply, and developing their theoretical description remains an important challenge in condensed matter physics. I will describe recent progress in understanding the dynamics of two systems without quasiparticles: (i) ultracold atoms in optical lattices, and (ii) the nematic quantum critical point of metals with applications to the `strange metal’ found in the high temperature superconductors. A combination of field-theoretic, holographic, and numerical methods will be used.
Igor Shovkovy, Arizona State University
Quantum Magnetic Phenomena: From QCD to Dirac semimetals
Studies of relativistic matter in strong magnetic fields attracted a lot of attention in recent years. Such studies are primarily motivated by the phenomenology of compact stars, the evolution of the Early Universe, and the physics of relativistic heavy ion collisions. Additionally, the outcomes of such research result in deeper understanding of a large class of novel condensed matter materials (e.g., graphene and Dirac semimetals. I will review recent surprises, ideas, and the progress made in understanding physical properties of relativistic matter in strong magnetic fields.
Sergey Sibiryakov, EPFL, CERN
From scale invariance to Lorentz symmetry
I will discuss the enhancement of space-time symmetries to Lorentz (rotation) invariance at the renormalization group fixed points of non-relativistic (anisotropic) field theories. Upon describing examples from the condensed matter physics, I will review the general argument for the stability of the infrared fixed points with the enhanced symmetry. Then I will focus on unitary field theories in (1+1) space-time dimensions which are invariant under translations, isotropic scale transformations and satisfy the requirement that the velocity of signal propagation is bounded from above. No a priori Lorentz invariance will be assumed. Still, I will prove that above properties are sufficient to ensure the existence of an infinite dimensional symmetry given by one or a product of several copies of conformal algebra. In particular, this implies presence of one or several Lorentz groups acting on the operator algebra of the theory. I will conclude by discussing the challenges in extending this result to higher space-time dimensions.
Dan Thanh Son, University of Chicago
Hydrodynamics and anomalies
Recently its has been found that relativistic hydrodynamics requires modifications in the presence of quantum anomalies. We will follow the theoretical developments that leads to this discovery and look at modern applications of hydrodynamics with anomalies.
Brian Swingle, Harvard University
Einstein's equations from qubits
I will outline a path by which a semi-classical geometry obeying Einstein's equations emerges holographically from elementary quantum mechanical objects undergoing local dynamics. The key idea is that entanglement between the quantum degrees of freedom leads to the emergence of a dynamical geometry, that entanglement is the fabric of spacetime. Furthermore, although important technical challenges remain, I will argue that the conceptual ideas are in place. The core of the talk will be two new results that are crucial to this program, one establishing a new representation of entanglement in RG tensor networks and the other showing that the equivalence principle is encoded in the universality of entanglement.
Omar Zanusso, SISSA
Functional renormalization group and statistical mechanics of membranes
We will first review the rich variety of universality classes of membranes and the various models developed to describe their mechanical properties. We will then discuss the recent applications of the non-perturbative renormalization group to these models aimed at improving the understanding of the membranes' phase-space beyond the epsilon-expansion. Finally, we will comment on the implications of these results on various physical systems.