Talks

9877 - 9888 of 16754 Results

Spin and Long-Range Forces: The Unfinished Tale of the Last Massless Particle

Natalia Toro Stanford University

November 13, 2013

PIRSA:13110047

Particle Physics
13/14 PSI - Condensed Matter - Lecture 3

Anushya Chandran Perimeter Institute for Theoretical Physics

Roger Melko University of Waterloo

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

November 13, 2013

PIRSA:13110029
13/14 PSI - Quantum Field Theory II - Lecture 3

Francois David CEA Saclay

November 13, 2013

PIRSA:13110010
General Relativity for Cosmology - Lecture 17

Achim Kempf University of Waterloo

November 12, 2013

PIRSA:13110001
Quantum mechanics as an operationally time symmetric probabilistic theory

Ognyan Oreshkov Université Libre de Bruxelles

November 12, 2013

PIRSA:13110057

Quantum Foundations
On Scale and Conformal Invariance in Four Dimensions

Anatoly Dymarsky Skolkovo Institute of Science and Technology

November 12, 2013

PIRSA:13110068

Quantum Fields and Strings
Baryogenesis from WIMPs

November 12, 2013

PIRSA:13110046

Particle Physics
Is there evidence for additional neutrino species from cosmology?

Stephen Feeney

November 12, 2013

PIRSA:13110083

Cosmology
13/14 PSI - Condensed Matter - Lecture 2

Anushya Chandran Perimeter Institute for Theoretical Physics

Roger Melko University of Waterloo

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

November 12, 2013

PIRSA:13110028
13/14 PSI - Quantum Field Theory II - Lecture 2

Francois David CEA Saclay

November 12, 2013

PIRSA:13110009
A universal Hamiltonian simulator: the full characterization

Gemma De Las Cuevas Universität Innsbruck

November 11, 2013

PIRSA:13110065

Quantum Information
New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT

November 11, 2013

PIRSA:13110081

Cosmology

Spin and Long-Range Forces: The Unfinished Tale of the Last Massless Particle

Natalia Toro Stanford University

November 13, 2013

PIRSA:13110047

Particle Physics

The success of gauge theory descriptions of Nature follows simply, in hindsight, from Lorentz symmetry, quantum mechanics, and the existence of interacting massless particles with spin. Yet, remarkably, the most generic type of massless particle spin has never been seriously examined: Wigner's so-called "continuous spin" particles (CSPs), which have a tower of polarization states carrying all integer or half-integer helicities that mix under boosts. I will explain recent progress in understanding these particles on two fronts: simple scattering amplitudes and a free quantum field theory. The scattering amplitudes give two remarkable insights into CSP physics. First, Lorentz symmetry protects CSP interactions from the dysfunction one might expect in a theory with infinitely many polarization states: divergent cross-sections and problematic thermodynamics. Second, and most intriguingly, CSP interactions approach those of ordinary scalars or helicity-1 or 2 gauge bosons in a high-energy "correspondence" regime. While a full interacting theory of CSPs remains elusive, these results suggest that any such theory would extend Maxwell electrodynamics and/or general relativity in a viable and testable way.
13/14 PSI - Condensed Matter - Lecture 3

Anushya Chandran Perimeter Institute for Theoretical Physics

Roger Melko University of Waterloo

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

November 13, 2013

PIRSA:13110029
13/14 PSI - Quantum Field Theory II - Lecture 3

Francois David CEA Saclay

November 13, 2013

PIRSA:13110010
General Relativity for Cosmology - Lecture 17

Achim Kempf University of Waterloo

November 12, 2013

PIRSA:13110001
Quantum mechanics as an operationally time symmetric probabilistic theory

Ognyan Oreshkov Université Libre de Bruxelles

November 12, 2013

PIRSA:13110057

Quantum Foundations

The standard formulation of quantum mechanics is operationally asymmetric with respect to time reversal---in the language of compositions of tests, tests in the past can influence the outcomes of test in the future but not the other way around. The question of whether this represents a fundamental asymmetry or it is an artifact of the formulation is not a new one, but even though various arguments in favor of an inherent symmetry have been made, no complete time-symmetric formulation expressed in rigorous operational terms has been proposed. Here, we discuss such a possible formulation based on a generalization of the usual notion of test. We propose to regard as a test any set of events between an input and an output system which can be obtained by an autonomously defined laboratory procedure. This includes standard tests, as well as proper subsets of the complete set of outcomes of standard tests, whose realization may require post-selection in addition to pre-selection. In this approach, tests are not expected to be operations that are up to the choices of agents---the theory simply says what circuits of tests may occur and what the probabilities for their outcomes would be, given that they occur. By virtue of the definition of test, the probabilities for the outcomes of past tests can depend on tests that take place in the future. Such theories have been previously called non-causal, but here we revisit that notion of causality. Using the Choi-Jamiolkowski isomorphism, every test in that formulation, commonly regarded as inducing transformations from an input to an output system, becomes equivalent to a passive detection measurement applied jointly on two input systems---one from the past and one from the future. This is closely related to the two-state vector formalism, but it comes with a conceptual revision: every measurement is a joint measurement on two separate systems and not on one system described by states in the usual Hilbert space and its dual. We thus obtain a static picture of quantum mechanics in space-time or more general structures, in which every experiment is a local measurement on a global quantum state that generalizes the recently proposed quantum process matrix. The existence of two types of systems in the proposed formalism allows us to define causation in terms of correlations without invoking the idea of intervention, offering a possible answer to the problem of the meaning of causation. The framework is naturally compatible with closed time-like curves and other exotic causal structures.
On Scale and Conformal Invariance in Four Dimensions

Anatoly Dymarsky Skolkovo Institute of Science and Technology

November 12, 2013

PIRSA:13110068

Quantum Fields and Strings

I will be discussing relation between scale and conformal symmetry in unitary Lorentz invariant QFTs in four dimensions.
Baryogenesis from WIMPs

November 12, 2013

PIRSA:13110046

Particle Physics

We propose a robust, unified framework, in which the similar baryon and dark matter cosmic abundances both arise from the physics of weakly interacting massive particles (WIMPs), with the rough quantitative success of the so-called “WIMP miracle”. In particular the baryon asymmetry arises from the decay of a meta-stable WIMP after its thermal freezeout at or below the weak scale. A minimal model and its embedding in R-parity violating (RPV) natural SUSY are studied as examples. The new mechanism saves RPV SUSY from the potential crisis of washing out primordial baryon asymmetry. We also consider the embedding of this idea in RPV split SUSY, where the mechanism works within the minimal model, and independently motivates the mini-split scale. Phenomenological implications for the LHC and precision tests are discussed.
Is there evidence for additional neutrino species from cosmology?

Stephen Feeney

November 12, 2013

PIRSA:13110083

Cosmology

It has been suggested that recent cosmological and flavor-oscillation data favor the existence of additional neutrino species beyond the three standard flavors. We apply Bayesian model selection to determine whether there is any evidence from current cosmological datasets for the standard cosmological model to be extended to include additional neutrino flavors. The datasets employed include cosmic microwave background temperature, polarization and lensing data, and measurements of the baryon acoustic oscillation scale and the Hubble constant. We also consider other additional neutrino physics, such as massive neutrinos, and possible degeneracies with other cosmological parameters.
13/14 PSI - Condensed Matter - Lecture 2

Anushya Chandran Perimeter Institute for Theoretical Physics

Roger Melko University of Waterloo

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

November 12, 2013

PIRSA:13110028
13/14 PSI - Quantum Field Theory II - Lecture 2

Francois David CEA Saclay

November 12, 2013

PIRSA:13110009
A universal Hamiltonian simulator: the full characterization

Gemma De Las Cuevas Universität Innsbruck

November 11, 2013

PIRSA:13110065

Quantum Information

We show that if the ground state energy problem of a classical spin model is NP-hard, then there exists a choice parameters of the model such that its low energy spectrum coincides with the spectrum of \emph{any} other model, and, furthermore, the corresponding eigenstates match on a subset of its spins. This implies that all spin physics, for example all possible universality classes, arise in a single model. The latter property was recently introduced and called ``Hamiltonian completeness'', and it was shown that several different models had this property. We thus show that Hamiltonian completeness is essentially equivalent to the more familiar complexity-theoretic notion of NP-completeness. Additionally, we also show that Hamiltonian completeness implies that the partition functions are the same. These results allow us to prove that the 2D Ising model with fields is Hamiltonian complete, which is substantially simpler than the previous examples of complete Hamiltonians. Joint work with Toby Cubitt.
New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT

November 11, 2013

PIRSA:13110081

Cosmology

Galaxy clusters form from the rarest peaks in the initial matter distribution, and hence are a sensitive probe of the amplitude of density fluctuations (sigma_8), the amount of matter in the universe, and the growth rate of structure. Galaxy clusters have the potential to constrain dark energy and neutrino masses. However, cluster cosmology is currently limited by systematic uncertainties due to poorly understood intracluster gas physics. I will present new statistical approaches to understand clusters and improve their cosmological constraining power through the thermal Sunyaev-Zel'dovich (tSZ) effect. First, I will describe a forthcoming first detection of the cross-correlation of the tSZ signal reconstructed from Planck data with the large-scale matter distribution traced by the Planck CMB lensing potential. This statistic measures the amount of hot gas found in moderately massive groups and clusters (M ~ 10^13-10^14.5 M_sun), a mass scale below that probed by direct cluster detections. Second, I will describe the first measurement of the PDF of the tSZ field using ACT 148 GHz maps. This measurement contains information from all (zero-lag) moments of the tSZ field, beyond simply the 2- or 3-point functions. It is a very sensitive probe of sigma_8 and may also provide a method with which to break the degeneracy between sigma_8 and uncertainties in the physics of the intracluster gas.

Title	Date	Collection	Type	Info
Spin and Long-Range Forces: The Unfinished Tale of the Last Massless Particle	2013‑11‑13	Colloquium	Scientific Series	View details
13/14 PSI - Condensed Matter - Lecture 3	2013‑11‑13	13/14 PSI - Condensed Matter	Course	View details
13/14 PSI - Quantum Field Theory II - Lecture 3	2013‑11‑13	13/14 PSI - Quantum Field Theory II	Course	View details
General Relativity for Cosmology - Lecture 17	2013‑11‑12	General Relativity for Cosmology - 2013	Course	View details
Quantum mechanics as an operationally time symmetric probabilistic theory	2013‑11‑12	Quantum Foundations	Scientific Series	View details
On Scale and Conformal Invariance in Four Dimensions	2013‑11‑12	Quantum Fields and Strings	Scientific Series	View details
Baryogenesis from WIMPs	2013‑11‑12	Particle Physics	Scientific Series	View details
Is there evidence for additional neutrino species from cosmology?	2013‑11‑12	Cosmology and Gravitation	Scientific Series	View details
13/14 PSI - Condensed Matter - Lecture 2	2013‑11‑12	13/14 PSI - Condensed Matter	Course	View details
13/14 PSI - Quantum Field Theory II - Lecture 2	2013‑11‑12	13/14 PSI - Quantum Field Theory II	Course	View details
A universal Hamiltonian simulator: the full characterization	2013‑11‑11	Perimeter Institute Quantum Discussions	Scientific Series	View details
New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT	2013‑11‑11	Cosmology and Gravitation	Scientific Series	View details

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