Scientific Series

Displaying 3529 - 3540 of 5164

The Quantum Steering Ellipsoid

Sania Jevtic Imperial College London
March 26, 2013

PIRSA:13030112
Quantum Foundations
Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions

Michael Hermele University of Colorado Boulder
March 26, 2013

PIRSA:13030116
Condensed Matter
Comments on short strings and Wilson loops in AdS/CFT
March 26, 2013

PIRSA:13030111
Quantum Fields and Strings
Effective field theory of the unstable top (quark)

Alexander Penin University of Alberta
March 26, 2013

PIRSA:13030090
Particle Physics
Supersymmetric gauge theory and the Yangian - continued

Kevin Costello Perimeter Institute for Theoretical Physics

March 26, 2013

PIRSA:13030115
Wick's theorem for Matrix Product states

Robert Huebener Freie Universität Berlin
March 25, 2013

PIRSA:13030117
Quantum Information
Dissecting holography with higher spins

Xi Yin Harvard University
March 25, 2013

PIRSA:13030098
Quantum Fields and Strings
Supersymmetric gauge theory and the Yangian

Kevin Costello Perimeter Institute for Theoretical Physics

March 25, 2013

PIRSA:13030114
Particle Acceleration by Magnetic Reconnection in Striped Pulsar Winds and Relativistic Jets

Lorenzo Sironi Columbia University
March 21, 2013

PIRSA:13030078
Strong Gravity
Frustrated Magnets and Quantum Spin Liquids

Steven White University of California, Irvine
March 20, 2013

PIRSA:13030097
Condensed Matter
Evidence for a new particle on the worldsheet of the QCD flux tube

Sergei Dubovsky New York University (NYU)
March 19, 2013

PIRSA:13030109
Quantum Fields and Strings
Learning what the Higgs is mixed with

Kunal Kumar Carleton University
March 19, 2013

PIRSA:13030089
Particle Physics

The Quantum Steering Ellipsoid

Sania Jevtic Imperial College London
March 26, 2013

PIRSA:13030112
Quantum Foundations
A quantum steering ellipsoid may be used to faithfully represent a density matrix ? describing two qubits A and B. The ellipsoid is the geometric set of states that Bob can steer Alice's qubit to when he implements all possible measurements on his qubit. We show how the correlations between qubits A and B manifest themselves in this paradigm, giving simple conditions for when the state is entangled, or has discord. We will also present novel features of the two qubit state that are revealed by the steering ellipsoid formalism, and show that a state corresponding to an ellipsoid with non-zero volume contains a new type of correlation.
Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions

Michael Hermele University of Colorado Boulder
March 26, 2013

PIRSA:13030116
Condensed Matter
Quantum number fractionalization is a remarkable property of topologically ordered states of matter, such as fractional quantum Hall liquids, and quantum spin liquids. For a given type of topological order, there are generally many ways to fractionalize the quantum numbers of a given symmetry. What does it mean to have different types of fractionalization? Are different types of fractionalization a universal property that can be used to distinguish phases of matter? In this talk, I will answer these questions, focusing on a simple class of topologically ordered phases, namely two-dimensional gapped Z2 spin liquids, and I will present a symmetry classification of these phases. I will also discuss efforts in progress to find microscopic models realizing different symmetry classes.
Comments on short strings and Wilson loops in AdS/CFT
March 26, 2013

PIRSA:13030111
Quantum Fields and Strings
In the study of the string/gauge theory duality (AdS/CFT), an important role is played by the relation between local operators and Wilson loops. Perhaps the most well known example is the relation between twist two operators and the light-like cusp Wilson loop. On the string side, the twist two operator is represented by a "long" string (GKP). In this talk I use T-duality to argue that such relation is also natural for "short" strings. I discuss some examples and present a map between the shape of a short string crossing the Poincare horizon and the shape of a corresponding Wilson loop.
Based on arXiv:1212.4886 with Arkady Tseytlin (Imperial College).
Effective field theory of the unstable top (quark)

Alexander Penin University of Alberta
March 26, 2013

PIRSA:13030090
Particle Physics
I introduce a new nonrelativistic effective field theory which systematically accounts for the finite lifetime effects in production of unstable particles.
The theory is applied to the threshold production of top quark-antiquark pairs.
Supersymmetric gauge theory and the Yangian - continued

Kevin Costello Perimeter Institute for Theoretical Physics

March 26, 2013

PIRSA:13030115

I'll explain a new connection between supersymmetric gauge theories and the Yangian. The main result is that a twisted, deformed version of the pure N=1 supersymmetric gauge theory is controlled by the Yangian, in the same way that Chern-Simons theory is controlled by the quantum group. This result is used to give an exact calculation, in perturbation theory, of the expectation value of a certain net of n+m Wilson operators in the deformed N=1 gauge theory. This expectation value coincides with the partition function of a spin-chain integrable lattice model on an n-by-m doubly-periodic lattice.
Wick's theorem for Matrix Product states

Robert Huebener Freie Universität Berlin
March 25, 2013

PIRSA:13030117
Quantum Information
Matrix product states and their continuous analogues are variational classes of states that capture quantum many-body systems or quantum fields with low entanglement; they are at the basis of the density-matrix renormalization group method and continuous variants thereof. In this talk we show that, generically, N-point functions of arbitrary operators in discrete and continuous translation invariant matrix product states are completely characterized by the corresponding two- and three-point functions. Aside from having important consequences for the structure of correlations in quantum states with low entanglement, this result provides a new way of reconstructing unknown states from correlation measurements e.g. for one-dimensional continuous systems of cold atoms. We argue that such a relation of correlation functions may help in devising perturbative approaches to interacting theories.

Joint work with Andrea Mari and Jens Eisert.
arXiv:1207.6537
Dissecting holography with higher spins

Xi Yin Harvard University
March 25, 2013

PIRSA:13030098
Quantum Fields and Strings
The holographic correspondence is a powerful duality between a quantum theory of gravity and a quantum gauge theory in one lower space-time dimension. Higher spin gravity theories, i.e. gravity theories that also contain (gauge) fields of spins greater than 2, play a special role in holography. I will explain consistent interacting higher spin gravity theories in anti-de Sitter space, their duality with gauged conformal vector models, and their connection to string theory.
Supersymmetric gauge theory and the Yangian

Kevin Costello Perimeter Institute for Theoretical Physics

March 25, 2013

PIRSA:13030114

I'll explain a new connection between supersymmetric gauge theories and the Yangian. The main result is that a twisted, deformed version of the pure N=1 supersymmetric gauge theory is controlled by the Yangian, in the same way that Chern-Simons theory is controlled by the quantum group. This result is used to give an exact calculation, in perturbation theory, of the expectation value of a certain net of n+m Wilson operators in the deformed N=1 gauge theory. This expectation value coincides with the partition function of a spin-chain integrable lattice model on an n-by-m doubly-periodic lattice.
Particle Acceleration by Magnetic Reconnection in Striped Pulsar Winds and Relativistic Jets

Lorenzo Sironi Columbia University
March 21, 2013

PIRSA:13030078
Strong Gravity
The relativistic wind of pulsars consists of toroidal stripes of opposite magnetic field polarity, separated by current sheets of hot plasma. By means of 2D and 3D particle-in-cell simulations, we investigate particle acceleration and magnetic field dissipation at the termination shock of a striped pulsar wind. At the shock, the flow compresses and the alternating fields annihilate by driven magnetic reconnection. Irrespective of the stripe wavelength "lambda" or the wind magnetization "sigma" (in the regime sigma>>1 of magnetically-dominated flows), shock-driven reconnection transfers all the magnetic energy of the alternating fields to the particles. As the value of lambda/(r_L*sigma) increases (here, r_L is the relativistic Larmor radius in the wind), the post-shock spectrum passes from a thermal Maxwellian to a flat power-law tail with slope around -1.5, populated by particles accelerated by the reconnection electric field. The limit lambda/(r_L*sigma)>>1 is realized in relativistic jets, where kink instabilities may seed the conditions for magnetic reconnection. Here, we find that the particle spectrum in the current sheet approaches a flat power-law tail with slope between -1.5 and -2, regardless of the conditions in the jet. The spectrum extends to higher energies for larger magnetizations or colder plasma temperatures, everything else being fixed. Our results place important constraints on the emission models of Pulsar Wind Nebulae and magnetically-dominated astrophysical jets.
Frustrated Magnets and Quantum Spin Liquids

Steven White University of California, Irvine
March 20, 2013

PIRSA:13030097
Condensed Matter
A quantum spin liquid is a solid whose atoms have magnetic moments but, because of quantum fluctuations, these moments fluctuate like a liquid even at zero temperature. Two dimensional spin liquids have been suggested as a way to produce high temperature superconductivity, and to build quantum computers. Just as helium is the only element which is a liquid at zero temperature, 2D spin liquids have been extremely difficult to find, despite decades of effort, raising the question, do realistic spin liquids even exist?
Recently, apparent spin liquids have been found experimentally, stimulating theoretical work to find simple model Hamiltonians of frustrated spin systems that have spin liquid ground states.

In this talk, I will give a broad overview of spin liquids and then focus on our simulations of the kagome Heisenberg model, a simple, realistic model of some of the recent experimental spin liquids, where we find a spin liquid ground state.
Evidence for a new particle on the worldsheet of the QCD flux tube

Sergei Dubovsky New York University (NYU)
March 19, 2013

PIRSA:13030109
Quantum Fields and Strings
We propose a new approach for the calculation of the spectrum of excitations of QCD flux tubes. It relies on the fact that the worldsheet theory is integrable at low energies. With this approach, energy levels can be calculated for much shorter flux tubes than was previously possible, allowing for a quantitative comparison with existing lattice data. The improved theoretical control makes it manifest that existing lattice data provides strong evidence for a new pseudoscalar particle localized on the QCD fluxtube - the worldsheet axion.
Learning what the Higgs is mixed with

Kunal Kumar Carleton University
March 19, 2013

PIRSA:13030089
Particle Physics
The Standard Model Higgs boson may be mixed with another scalar that does not couple singly to gauge bosons or fermions. The electroweak quantum numbers of such an additional scalar can be determined by measuring the quartic Higgs-Higgs-vector-vector couplings, which contribute—along with the coveted triple Higgs coupling—to double Higgs production in e+e− collisions. We show that simultaneous sensitivity to the quartic Higgs-Higgs-vector-vector coupling and the triple Higgs coupling can be obtained using measurements of the double Higgs production cross section at two different e+e− center-of-mass energies. Kinematic distributions of the two Higgs bosons in the final state could provide additional discriminating power.

Title	Speaker(s)	Date	Talk Type	Info link
The Quantum Steering Ellipsoid	Sania Jevtic	2013-03-26	Scientific Series	View details
Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions	Michael Hermele	2013-03-26	Scientific Series	View details
Comments on short strings and Wilson loops in AdS/CFT		2013-03-26	Scientific Series	View details
Effective field theory of the unstable top (quark)	Alexander Penin	2013-03-26	Scientific Series	View details
Supersymmetric gauge theory and the Yangian - continued	Kevin Costello	2013-03-26	Scientific Series	View details
Wick's theorem for Matrix Product states	Robert Huebener	2013-03-25	Scientific Series	View details
Dissecting holography with higher spins	Xi Yin	2013-03-25	Scientific Series	View details
Supersymmetric gauge theory and the Yangian	Kevin Costello	2013-03-25	Scientific Series	View details
Particle Acceleration by Magnetic Reconnection in Striped Pulsar Winds and Relativistic Jets	Lorenzo Sironi	2013-03-21	Scientific Series	View details
Frustrated Magnets and Quantum Spin Liquids	Steven White	2013-03-20	Scientific Series	View details
Evidence for a new particle on the worldsheet of the QCD flux tube	Sergei Dubovsky	2013-03-19	Scientific Series	View details
Learning what the Higgs is mixed with	Kunal Kumar	2013-03-19	Scientific Series	View details

Scientific Series

Format results