Scientific Series

Displaying 3445 - 3456 of 5007

Exploiting the Strong Gravitational Fields of Neutron Stars to Measure their Properties

Dimitrios Psaltis University of Arizona
February 28, 2013

PIRSA:13020126
General Relativity & Quantum Cosmology
Quantum Gravity as Random Geometry

Vincent Rivasseau University of Paris-Saclay
February 27, 2013

PIRSA:13020132
General Relativity & Quantum Cosmology
The universe as a process of unique events

Lee Smolin Perimeter Institute for Theoretical Physics
February 26, 2013

PIRSA:13020146
Quantum Physics
Quantum Computation vs. Firewalls

Daniel Harlow Massachusetts Institute of Technology (MIT)
February 26, 2013

PIRSA:13020138
Quantum Physics

High Energy Physics
DMRG Studies on the Spin Liquid Ground State of the Kagome Model

Stefan Depenbrock Ludwig-Maximilians-Universitiät München (LMU)
February 26, 2013

PIRSA:13020147
Condensed Matter
FERMI 130 GeV Line: Dark Interpretations

Matthew McCullough Massachusetts Institute of Technology (MIT)
February 26, 2013

PIRSA:13020150
High Energy Physics
Newton’s Method in Cosmology Today

Bill Harp Western University
February 26, 2013

PIRSA:13020151
Astrophysics
Bounding the purification rank of mixed states

Gemma De Las Cuevas Universität Innsbruck
February 25, 2013

PIRSA:13020149
Quantum Physics
Beyond Massive Gravity

Rachel Rosen Carnegie Mellon University
February 25, 2013

PIRSA:13020134
Astrophysics
Gamma Rays at 130 GeV and How They Might Come from Dark Matter

Andrew Frey University of Winnipeg
February 21, 2013

PIRSA:13020139
Astrophysics

General Relativity & Quantum Cosmology
The Evolution of Quasars with Cosmic Time

Michael Strauss Princeton University

February 20, 2013

PIRSA:13020120
A K matrix construction of symmetry enriched phases
February 20, 2013

PIRSA:13020140
Condensed Matter

Exploiting the Strong Gravitational Fields of Neutron Stars to Measure their Properties

Dimitrios Psaltis University of Arizona
February 28, 2013

PIRSA:13020126
General Relativity & Quantum Cosmology
Neutron stars possess the strongest gravitational fields among stellar objects in the Universe that are not surrounded by a horizon. This causes the emission from their surfaces to be strongly lensed and deformed. Two upcoming space X-ray missions, ESA's LOFT and NASA's NICER, aim to use observations of lightcurves from spinning neutron stars to map their gravitational fields as well as measure their masses and radii. In this talk, I will discuss some unexpected strong-field phenomena that affect gravitational lensing in the vicinity of neutron stars. I will then show how we can use these phenomena to measure strong-field frame dragging and break degeneracies in the measured neutron-star masses and radii.
Quantum Gravity as Random Geometry

Vincent Rivasseau University of Paris-Saclay
February 27, 2013

PIRSA:13020132
General Relativity & Quantum Cosmology
Matrix models, random maps and Liouville field theory are prime tools which connect random geometry and quantum gravity in two dimensions. The tensor track is a new program to extend this connection to higher dimensions through the corresponding notions of tensor models, colored triangulations and tensor group field theories.
The universe as a process of unique events

Lee Smolin Perimeter Institute for Theoretical Physics
February 26, 2013

PIRSA:13020146
Quantum Physics
Quantum Computation vs. Firewalls

Daniel Harlow Massachusetts Institute of Technology (MIT)
February 26, 2013

PIRSA:13020138
Quantum Physics

High Energy Physics
DMRG Studies on the Spin Liquid Ground State of the Kagome Model

Stefan Depenbrock Ludwig-Maximilians-Universitiät München (LMU)
February 26, 2013

PIRSA:13020147
Condensed Matter
I will present a density-matrix renormalization group (DMRG) study of the S=1/2 Heisenberg antiferromagnet on the kagome lattice to identify the conjectured spin liquid ground state. Exploiting SU(2) spin symmetry, which allows us to keep up to 16,000 DMRG states, we consider cylinders with circumferences up to 17 lattice spacings and find a spin liquid ground state with an estimated per site energy of -0.4386(5), a spin gap of 0.13(1), very short-range decay in spin, dimer and chiral correlation functions and finite topological entanglement consistent with the logarithm of 2, ruling out gapless, chiral or non-topological spin liquids. All this would provide strong evidence for a gapped topological Z_2 spin liquid.
FERMI 130 GeV Line: Dark Interpretations

Matthew McCullough Massachusetts Institute of Technology (MIT)
February 26, 2013

PIRSA:13020150
High Energy Physics
Last year strong evidence was claimed for a 130 GeV gamma ray line from the galactic center in the FERMI telescope data. In the first half of the talk I will review the status of the evidence, including recent suggestions which call it into question. In the second half of the talk, under the bold assumption that the line is a genuine signature of dark matter, I will review some of the properties required of dark matter to explain the line and the general features of models proposed to explain it. This second half will include material from recent work with Francesco D'Eramo and Jesse Thaler (arxiv:1210.7817), which suggests that the line is readily explained by dark matter "semi-annihilation" rather than the standard annihilation interpretation.
Newton’s Method in Cosmology Today

Bill Harp Western University
February 26, 2013

PIRSA:13020151
Astrophysics
Newton’s inferences from phenomena realize an ideal of empirical success that’s richer than prediction. To realize Newton’s richer conception of empirical success a theory needs to do more than to accurately predict the phenomena it purports to explain: in addition it needs to have the phenomena accurately measure parameters of the theory. Newton’s method aims to turn theoretical questions into ones which can be empirically answered by measurements from phenomena. Propositions inferred from phenomena are provisionally accepted as guides to further research. Newton’s ideal of empirical success as agreeing measurements from diverse phenomena is appealed to in support of the radical inference to dark energy in cosmology today. Robert Kirshner (two of his PhDs share one half of 2011’s Nobel Prize in physics) gave an account of the role of cosmic microwave background measurements, to back up the supernova measurements and measurements from galaxy clustering in supporting the transition of dark energy from a wild hypothesis into an accepted background assumption that guides further research in cosmology today. This illustrates a feature of agreeing measurements from diverse phenomena that is especially important for turning data into evidence. To the extent that the sources of systematic error of the different measurements can be regarded as independent, their agreement contributes additional support for counting them as accurate rather than as mere artifacts of systematic error.
Bounding the purification rank of mixed states

Gemma De Las Cuevas Universität Innsbruck
February 25, 2013

PIRSA:13020149
Quantum Physics
A mixed state can be expressed as a sum of D tensor product matrices, where D is its operator Schmidt rank, or as the result of a purification with a purifying state of Schmidt rank D', where D' is its purification rank. The question whether D' can be upper bounded by D is important theoretically (to establish a description of mixed states with tensor networks), as well as numerically (as the first decomposition is more efficient, but the second one guarantees positive-semidefiniteness after truncation). Here we show that no upper bounds of the purification rank that depend only on operator Schmidt rank exist, but provide upper bounds that also depend on the number of eigenvalues. In addition, we formulate the approximation problem as a Semidefinite Program.
Joint work with N. Schuch, D. Perez-Garcia, and J. I. Cirac.
Beyond Massive Gravity

Rachel Rosen Carnegie Mellon University
February 25, 2013

PIRSA:13020134
Astrophysics
In the last few years there has been a burst of progress in the field of massive gravity. The construction of consistent theories in which the graviton has a small mass has in turn led to the development a new family of compelling, consistent low-energy modifications of General Relativity. These theories improve our understanding of the interplay between gravity and particle physics and provide new approaches to solving the cosmological constant problem. In this talk I will review these recent developments. I will discuss the search among these new theories for a symmetry that has the potential to address the cosmological constant problem.
Gamma Rays at 130 GeV and How They Might Come from Dark Matter

Andrew Frey University of Winnipeg
February 21, 2013

PIRSA:13020139
Astrophysics

General Relativity & Quantum Cosmology
Gamma Rays at 130 GeV and How They Might Come from Dark Matter" I'll discuss the exciting (but somewhat controversial) new discovery of a sharp gamma ray feature at 130 GeV from near the galactic center and review some other evidence that might link it to annihilation of dark matter. I will then explain the challenges in understanding how dark matter might produce this signal and explain a model or two that overcome these difficulties.
The Evolution of Quasars with Cosmic Time

Michael Strauss Princeton University

February 20, 2013

PIRSA:13020120

While the luminosity and mass distributions of quasars has evolved dramatically with cosmic time, the physical properties of quasars of a given luminosity are remarkably independent of redshift. I will describe recent results on the spectra of luminous quasars, the dark matter halos in which they sit, and the intergalactic medium of their host galaxies, that are essentially indistinguishable from moderate redshifts to z>6. The one property apparently unique to the highest-redshift quasars is that some small fraction show evidence for having very little infrared excess from hot dust. Dust obscuration is another theme in quasar studies; an appreciable fraction of the growth of black holes may be hidden at optical wavelengths by dust. I will describe searches for obscured quasars at high redshift and low, and studies of their demographics and physical properties.
A K matrix construction of symmetry enriched phases
February 20, 2013

PIRSA:13020140
Condensed Matter
We construct in the K matrix formalism concrete examples of symmetry enriched topological phases, namely intrinsically topological phases with global symmetries. We focus on the Abelian and non-chiral topological phases and demonstrate by our examples how the interplay between the global symmetry and the fusion algebra of the anyons of a topologically ordered system determines the existence of gapless edge modes protected by the symmetry and that a (quasi)-group structure can be defined among these phases. Our examples include phases that display charge fractionalization and more exotic non-local anyon exchange under global symmetry that correspond to general group extensions of the global symmetry group.

Title	Speaker(s)	Date	Talk Type	Info link
Exploiting the Strong Gravitational Fields of Neutron Stars to Measure their Properties	Dimitrios Psaltis	2013-02-28	Scientific Series	View details
Quantum Gravity as Random Geometry	Vincent Rivasseau	2013-02-27	Scientific Series	View details
The universe as a process of unique events	Lee Smolin	2013-02-26	Scientific Series	View details
Quantum Computation vs. Firewalls	Daniel Harlow	2013-02-26	Scientific Series	View details
DMRG Studies on the Spin Liquid Ground State of the Kagome Model	Stefan Depenbrock	2013-02-26	Scientific Series	View details
FERMI 130 GeV Line: Dark Interpretations	Matthew McCullough	2013-02-26	Scientific Series	View details
Newton’s Method in Cosmology Today	Bill Harp	2013-02-26	Scientific Series	View details
Bounding the purification rank of mixed states	Gemma De Las Cuevas	2013-02-25	Scientific Series	View details
Beyond Massive Gravity	Rachel Rosen	2013-02-25	Scientific Series	View details
Gamma Rays at 130 GeV and How They Might Come from Dark Matter	Andrew Frey	2013-02-21	Scientific Series	View details
The Evolution of Quasars with Cosmic Time	Michael Strauss	2013-02-20	Scientific Series	View details
A K matrix construction of symmetry enriched phases		2013-02-20	Scientific Series	View details

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Format results

Exploiting the Strong Gravitational Fields of Neutron Stars to Measure their Properties

Quantum Gravity as Random Geometry

The universe as a process of unique events

Quantum Computation vs. Firewalls

DMRG Studies on the Spin Liquid Ground State of the Kagome Model

FERMI 130 GeV Line: Dark Interpretations

Newton’s Method in Cosmology Today

Bounding the purification rank of mixed states

Beyond Massive Gravity

Gamma Rays at 130 GeV and How They Might Come from Dark Matter

The Evolution of Quasars with Cosmic Time

A K matrix construction of symmetry enriched phases

Exploiting the Strong Gravitational Fields of Neutron Stars to Measure their Properties

Quantum Gravity as Random Geometry

The universe as a process of unique events

Quantum Computation vs. Firewalls

DMRG Studies on the Spin Liquid Ground State of the Kagome Model

FERMI 130 GeV Line: Dark Interpretations

Newton’s Method in Cosmology Today

Bounding the purification rank of mixed states

Beyond Massive Gravity

Gamma Rays at 130 GeV and How They Might Come from Dark Matter

The Evolution of Quasars with Cosmic Time

A K matrix construction of symmetry enriched phases