Scientific Series

Displaying 3409 - 3420 of 5012

The universe as a process of unique events

Lee Smolin
Perimeter Institute for Theoretical Physics
February 26, 2013

PIRSA:13020146
Quantum Foundations
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
Quantum Computation vs. Firewalls

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

PIRSA:13020138
Quantum Information

Quantum Fields and Strings
FERMI 130 GeV Line: Dark Interpretations

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

PIRSA:13020150
Particle Physics
Newton’s Method in Cosmology Today

Bill Harp
Western University
February 26, 2013

PIRSA:13020151
Cosmology
Bounding the purification rank of mixed states

Gemma De Las Cuevas
Universität Innsbruck
February 25, 2013

PIRSA:13020149
Quantum Information
Beyond Massive Gravity

Rachel Rosen
Carnegie Mellon University
February 25, 2013

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

Andrew Frey
University of Winnipeg
February 21, 2013

PIRSA:13020139
Cosmology

Strong Gravity
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
Wall-Crossing and Quiver Invariants

Piljin Yi
Korea Institute for Advanced Study
February 19, 2013

PIRSA:13020137
Quantum Fields and Strings
Qanti-kt: Nondeterministic jet clustering

David Krohn
Harvard University
February 19, 2013

PIRSA:13020135
Particle Physics

The universe as a process of unique events

Lee Smolin
Perimeter Institute for Theoretical Physics
February 26, 2013

PIRSA:13020146
Quantum Foundations
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.
Quantum Computation vs. Firewalls

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

PIRSA:13020138
Quantum Information

Quantum Fields and Strings
FERMI 130 GeV Line: Dark Interpretations

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

PIRSA:13020150
Particle 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
Cosmology
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 Information
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
Cosmology
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
Cosmology

Strong Gravity
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.
Wall-Crossing and Quiver Invariants

Piljin Yi
Korea Institute for Advanced Study
February 19, 2013

PIRSA:13020137
Quantum Fields and Strings
We start with a one-slide review of the Kontsevich-Soibelman (KS) solution to the wall-crossing problem and then proceed to direct and comprehensive physics counting of BPS states that eventually connects to KS. We also asks what input data is needed for either approaches to produce complete BPS spectra, and this naturally leads to the BPS quiver representation of BPS states and the new notion of quiver invariants.
We propose a simple geometrical conjecture that can segregate BPS states in Higgs phases of the BPS quiver dynamics to those that experience wall-crossing and those that do not, and give
proofs for all cyclice Abelian quivers. We close with explanation of how physics distinguishes two such classes of BPS states.
Qanti-kt: Nondeterministic jet clustering

David Krohn
Harvard University
February 19, 2013

PIRSA:13020135
Particle Physics
The interpretation of events with jets is often ambiguous, especially for the sort of highly complex events one encounters at the LHC. One often finds that an event interpreted as signal-like using one choice of jet algorithm and radius parameter is no longer signal-like with another, even if the two are very similar. Here we present an extension of the Qjets procedure designed to account for this ambiguity and assign each plausible interpretation of an event a weight, so that events which are unambiguously signal-like carry more influence on one's results than events which are only marginally so. This procedure can be used with any existing analysis employing a sequential recombination algorithm like anti-kT and we will show that through its use the statistical power of an analysis often increases. In particular, we will see that a up to a 20\% improvement in statistical significance can be realized for a Higgs-like analysis searching for a resonance recoiling against an associated vector boson.

Title	Speaker(s)	Date	Talk Type	Info link
The universe as a process of unique events	Lee Smolin	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
Quantum Computation vs. Firewalls	Daniel Harlow	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
Wall-Crossing and Quiver Invariants	Piljin Yi	2013-02-19	Scientific Series	View details
Qanti-kt: Nondeterministic jet clustering	David Krohn	2013-02-19	Scientific Series	View details

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