The CTP Lunch Club meets every Friday at noon in the Cosman seminar room, 6C-442 (provided that there are sufficient speakers). A light lunch will be provided begining at 11:50am (usually pizza, however some other options may be explored).
The seminars are designed for graduate students and should be accessible to all students. First year students are particularly encouraged to attend so that they may learn about research being performed in the CTP. The goal is learning, and to encourage participation, the seminars will be for students only.
Email notification of the club will be sent to the ctp-all, ctp-postdocs and ctp-students email lists as appropriate. If you wish to speak, or have suggestions about speakers and/or possible workshop topics, please contact the organizers, Riccardo Abbate and Teppo Jouttenus.
Gauge symmetry is a cornerstone of modern theoretical particle physics, but it differs from other symmetries in that it does not relate different physical configurations: instead, it implies that different mathematical descriptions correspond to the same physical configuration. I will briefly review how this mathematical redundancy inevitably results from an attempt to accomodate spin-1 massless particles into a Lorentz-invariant framework. I will also consider the close parallel between this and general coordinate invariance, which results from accomodating spin-2 massless particles and which leads to General Relativity (GR).Next I will discuss the famous --but suprisingly subtle-- Weinberg-Witten theorem, which forbids massless particles with spin in relativistic theories with conserved currents and stress-energy tensors. I will explain why Yang-Mills, GR, string theory, and AdS/CFT evade the Weinberg-Witten theorem, and why the theorem implies that attempts to formulate an "emergent gravity" must abandon Minkowski spacetime as a starting point, or do away with exact Lorentz invariance for the underlying physics.
Gravity duals for non relativistic conformal field theories
The AdS/CFT correspondence is the equivalence between a relativistic conformal field theory and a gravity theory (or string theory) in a higher dimensional space (AdS). More recently, there have been attempts to use this correspondence to study CFTs arising from condensed matter systems.Some systems exhibit a relativistic dispersion relations and the dynamics near a critical point of such systems is described by a relativistic conformal field theory. Most condensed matter systems are described by non-relativistic theories. Is it possible to generalize this correspondence to non-relativistic conformal field theories? There is a family of metrics which realize the Galilean symmetries as their isometries.
I will present a brief review of some recent work on gravity duals of non-relativistic conformal field theories.
This talk is intended for graduate students and is based on
hep-th/0804.4053, 0804.3972, 0807.1099, 1100, 1111.Postdocs and faculty
are welcome to attend.
Thermal Anti-de Sitter Space
Anti-de Sitter space has a special property that it undergoes a phase transition between a purely thermal radiation solution to an anti-de Sitter black hole solution, known as the Hawking-Page transition. This can be applied in the framework of the AdS/CFT correspondence to talk about what this thermal phase transition means for gauge theories. I will review some of the properties of anti-de Sitter space and it's thermal extensions, then discuss the Hawking-Page transition and it's CFT equivalen
Information, Entanglement, and the Wilds of Hilbert Space
This talk is motivated by the observation that, for systems with many degrees of freedom, Hilbert space is a very big place. I will explain this statement and what it has to do with physics using the concepts of information and entanglement. Along the way, we'll meet strange beasts like entanglement entropy and the "typical" quantum state. I will argue that Hilbert space has many unexplored regions, some of which may contain interesting physics. Finally, I will preview some of the new tools being developed to explore the wilds of Hilbert space.
Andrea de Simone
Eternal inflation and its oddities
I will start with a panegyric of the successes of inflation in explaining many observed features of our universe. The focus is then turned on the mechanism of eternal inflation, which suggests that our universe is only one among an infinite number of "bubble universes". I will discuss the ambiguity of extracting predictions in this setup and a possible solution. Some oddities of the multiverse picture, like the appearence of "Boltzmann Brains", will also be presented.
Nonrelativistic conformal field theories in cold atoms
I will give an introduction to physics studied in cold atoms and discuss some interesting aspects. Spin-1/2 fermions with point-like interaction fine-tuned to the infinite scattering length (fermions at unitarity) can be realized in cold atom experiments and is described by a nonrelativistic conformal field theory. I will show that there is a correspondence between scaling dimensions of primary operators and energy eigenvalues in a harmonic potential. I will give an example by computing scaling dimensions of a two-body composite operator.
Postdocs and Faculties are welcome
Entanglement, reduced density matrices, and the no-cloning and no-signaling theorems
The study of quantum mechanics usually focuses on the states of rather simple physical systems, Hamiltonian evolution, and the statistics of measurements of operators. Quantum information theory is a different perspective, in which one assumes that an experimenter has absolute control over the evolution of a quantum system and can perform arbitrarily detailed measurements. The goal is to develop frameworks for thinking abstractly about such experiments and understanding their fundamental limits.
As a very brief introduction to quantum information theory, I present a very general framework for discussing measurements (POVMs) and the density matrix formulation of quantum mechanics. I describe statistics of pieces of larger quantum systems by the reduced density matrix, and I introduce the Schmidt decomposition as a useful tool for understanding these systems. Finally, I prove two central theorems in quantum information: no cloning and no signaling.
Postdocs and Faculties are welcome to attend.
PDFs, GPDs, Nucleon Structure, and the Lattice
Parton Distribution Functions (PDFs) provide a rich and intuitive context in which to study the structure of the proton. In this talk, I will discuss how PDFs can give us information about the quark substructure of the proton in momentum, position, and spin space. I will start with the definition of PDFs in terms of matrix elements of quark operators, and from there show how they can be generalized to distributions in impact parameter space. In the second half of the talk, I will give a skeletal discussion of how moments of PDFs can be calculated on the lattice, and I will show sample results.
Postdocs are welcome to attend.
From QCD to High Tc
Lattice Gauge Theory of Strongly Correlated Systems
I will give a brief introduction to the Physics of Strongly Correlated Systems. Then I will talk about Lattice Gauge Theory and its application to such systems. My major focus is on the Hubbard model and the large U limit of it which leads to so called t-J model, generally accepted as the model Hamiltonian responsible for High Tc. In this talk I will introduce another Hamiltonian which we have found recently and seems to be equivalent to the Hubbard model (in some sense it is dual to the Hubbard model).
Then I will show that this Hamiltonian has gauge symmetry and leads to superconductivity. Finally I will argue that it captures the physics of strongly correlated systems more clearly and one can easily use perturbation theory to study this dual theory.
Faculty and Postdocs are welcome to attend.
The Search for a Holographic Dual of Our Universe
As the universe we live in has a positive cosmological constant, it would be nice to have a framework of understanding quantum gravity in de Sitter space-time, possibly by some kind of holographic duality. This framework would have to take bubble nucleation in to consideration. I will review the work of Freivogel, Sekino, Susskind and Yeh which proposes a possible duality of this kind in 4 dimensions. I will also present some recent two point function calculations that builds upon their idea.
Faculty and Postdocs are welcome to attend.
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