Scientific Series

Displaying 3493 - 3504 of 5123

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 Effective Field Theory of Large Scale Structures

Enrico Pajer Utrecht University
March 19, 2013

PIRSA:13030110
Cosmology
A CDT Hamiltonian from Horava-Lifshitz gravity

Yuki Sato Nagoya University
March 14, 2013

PIRSA:13030091
Quantum Gravity
The dynamics of asymptotically anti-de Sitter spacetimes

Claude Warnick
March 14, 2013

PIRSA:13030077
Strong Gravity
The Higgs confronts 3 universes at the LHC

Markus Luty University of California, Davis
March 13, 2013

PIRSA:13030095
Particle Physics
Neorealism and the Internal Language of Topoi

Sander Wolters Radboud Universiteit Nijmegen
March 12, 2013

PIRSA:13030107
Quantum Foundations

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.
The Effective Field Theory of Large Scale Structures

Enrico Pajer Utrecht University
March 19, 2013

PIRSA:13030110
Cosmology
An analytical understanding of large-scale matter inhomogeneities is an important cornerstone of our cosmological model and helps us interpreting current and future data. The standard approach, namely Eulerian perturbation theory, is unsatisfactory for at least three reasons: there is no clear expansion parameter since the density contrast is not small everywhere; it does not consistently account for deviations at large scales from a perfect pressureless fluid induced by short-scale non-linearities; for generic initial conditions, loop corrections are UV divergent, making predictions cutoff dependent and hence unphysical. I will present the systematic construction of an Effective Field Theory of Large Scale Structures and show that it successfully addresses all of the above issues. The idea is to smooth the density and velocity fields on a scale larger than the non-linear scale. The resulting smoothed fields are then small everywhere and provide a well-defined small parameter for perturbation theory. Smoothing amounts to integrating out the short scales, whose non-linear dynamics is hard to describe analytically. Their effects on the large scales are then determined by the symmetries of the problems. They introduce additional terms in the fluid equations such as an effective pressure, dissipation and stochastic noise. These terms have exactly the right scale dependence to cancel all divergences at one loop, and this should hold at all loops.
I will present a clean example of the renormalization of the theory in an Einstein de Sitter universe with self-similar initial conditions and discuss the relative importance of loop and effective corrections.
A CDT Hamiltonian from Horava-Lifshitz gravity

Yuki Sato Nagoya University
March 14, 2013

PIRSA:13030091
Quantum Gravity
Causal Dynamical Triangulations” (CDT) is a lattice theory where aspects of quantum gravity can be studied. Two-dimensional CDT can be solved analytically and the continuum (quantum) Hamiltonian obtained.
In this talk I will show that this continuum Hamiltonian is the one obtained by quantizing two-dimensional projectable Horava-Lifshitz gravity.
The dynamics of asymptotically anti-de Sitter spacetimes

Claude Warnick
March 14, 2013

PIRSA:13030077
Strong Gravity
The majority of work on asymptotically anti-de Sitter spacetimes, much of it motivated by the AdS/CFT correspondence, assumes configurations which are either at or close to equilibrium. Recently it has been discovered that genuinely dynamical spacetimes with AdS asymptotics can exhibit some surprising behaviour. In particular, numerical studies suggest AdS is dynamically unstable. I will discuss recent analytical (in)stability results for asymptotically AdS spacetimes, in particular how stability can be affected by boundary conditions at the timelike conformal infinity.
The Higgs confronts 3 universes at the LHC

Markus Luty University of California, Davis
March 13, 2013

PIRSA:13030095
Particle Physics
The recent discovery of the Higgs boson is a fundamental advance in particle physics. This talk gives a theorist's perspective of the significance of this discovery. The Higgs boson was proposed in the 1960s, but it is best understood in the context of the quest to understand the weak interactions, which began with Fermi's theory of weak interactions almost 80 years ago. This has led to three very different paradigms for the structure of fundamental interactions at the TeV scale: supersymmetry, compositeness/extra dimensions, and anthropic selection. The Large Hadron Collider is the experimentum crucis for deciding between these different possible universes, and the discovery of the Higgs is a crucial clue. This talk will describe these paradigms, the implications of the Higgs discovery for them, and the outlook for further discoveries that would decide between them.
Neorealism and the Internal Language of Topoi

Sander Wolters Radboud Universiteit Nijmegen
March 12, 2013

PIRSA:13030107
Quantum Foundations
Crudely formulated, the idea of neorealism, in the way that Chris Isham and Andreas Doering use it, means that each theory of physics, in its mathematical formulation should share certain structural properties of classical physics. These properties are chosen to allow some degree of realism in the interpretation (for example, physical variables always have values). Apart from restricting the form of physical theories, neorealism does increase freedom in the shape of physical theories in another way. Theories of physics may be interpreted in other topoi than the category of sets and functions. In my talk I will concentrate on two topos models for quantum theory. The contravariant model of Butterfield, Isham and Doering on the one hand, and the covariant model of Heunen, Landsman and Spitters on the other. I will argue that when we think of the topoi as generalized categories of sets (i.e. when we use the internal perspective of the topoi at hand), these two models are closely related, and both resemble classical physics. I will assume no background knowledge in topos theory.

Title	Speaker(s)	Date	Talk Type	Info link
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
The Effective Field Theory of Large Scale Structures	Enrico Pajer	2013-03-19	Scientific Series	View details
A CDT Hamiltonian from Horava-Lifshitz gravity	Yuki Sato	2013-03-14	Scientific Series	View details
The dynamics of asymptotically anti-de Sitter spacetimes	Claude Warnick	2013-03-14	Scientific Series	View details
The Higgs confronts 3 universes at the LHC	Markus Luty	2013-03-13	Scientific Series	View details
Neorealism and the Internal Language of Topoi	Sander Wolters	2013-03-12	Scientific Series	View details

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