Scientific Series

Displaying 3397 - 3408 of 5090

The World is Discrete

Olaf Dreyer Freelance Consultant
September 19, 2013

PIRSA:13090073
General Relativity & Quantum Cosmology
Short Gamma-Ray Bursts and the Electromagnetic Counterparts of Gravitational Wave Sources

Edo Berger Harvard University

September 18, 2013

PIRSA:13090050
Self-organized topological state with Majorana fermions

Marcel Franz University of British Columbia
September 17, 2013

PIRSA:13090071
Condensed Matter
Coalgebras, Models and Logics for Quantum Systems
September 17, 2013

PIRSA:13090072
Quantum Physics
Orbifolds and topological defects

Daniel Plencner Ludwig-Maximilians-Universität München (LMU)
September 17, 2013

PIRSA:13090061
High Energy Physics
ΛCDM Large Scale Triumphs and Small Scale Challenges

Joel Primack University of California, Santa Cruz
September 17, 2013

PIRSA:13090066
Astrophysics
Edge states at domain wall junctions in supersymmetric gauge theory

Davide Gaiotto Perimeter Institute for Theoretical Physics
September 13, 2013

PIRSA:13090074
Condensed Matter
Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Donald Marolf University of California, Santa Barbara
September 12, 2013

PIRSA:13090060
General Relativity & Quantum Cosmology
Quantum States are Consistent Probability Distributions

Nadish de Silva University of Oxford
September 12, 2013

PIRSA:13090070
Quantum Physics
The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe
September 11, 2013

PIRSA:13090065
High Energy Physics
Quantum Observables as Real-valued Functions and Quantum Probability
September 10, 2013

PIRSA:13090068
Quantum Physics
From dlogs to dilogs

Arthur Lipstein Durham University
September 10, 2013

PIRSA:13090049
High Energy Physics

The World is Discrete

Olaf Dreyer Freelance Consultant
September 19, 2013

PIRSA:13090073
General Relativity & Quantum Cosmology
We argue that the scale-free spectrum that is observed in the cosmic microwave background is the result of a phase transition in the early universe. The observed tilt of the spectrum, which has been measured to be 0.04, is shown to be equal to the anomalous scaling dimension of the correlation function. The phase transition replaces inflation as the mechanism that produces this spectrum. The tilt further indicates that there is a fundamental small length scale in nature that we have not yet observed in any other way.
Short Gamma-Ray Bursts and the Electromagnetic Counterparts of Gravitational Wave Sources

Edo Berger Harvard University

September 18, 2013

PIRSA:13090050

Gamma-ray bursts are the most luminous and energetic explosions known in the universe. They appear in two varieties: long- and short-duration. The long GRB result from the core-collapse of massive stars, but until recently the origin of the short GRBs was shrouded in mystery. In this talk I will present several lines of evidence that point to the merger of compact objects binaries (NS-NS and/or NS-BH) as the progenitor systems of short GRBs. Within this framework, the observational data also allow us to independently determine the merger rate of these systems as input to the Advanced LIGO event rate, to infer the merger distribution timescale, and to determine the energy scale of the mergers. In addition, using radio to X-ray observations of short GRBs we can determine the expected electromagnetic properties of Advanced LIGO sources.
Self-organized topological state with Majorana fermions

Marcel Franz University of British Columbia
September 17, 2013

PIRSA:13090071
Condensed Matter
Topological phases, quite generally, are difficult to come by. They either occur under rather extreme conditions (e.g. the quantum Hall liquids, which require high sample purity, strong magnetic fields and low temperatures) or demand fine tuning of system parameters, as in the majority of known topological insulators. Many perfectly sensible topological phases, such as the Weyl semimetals and topological superconductors, remain experimentally undiscovered. In this talk I will introduce a system in which a key dynamical parameter adjusts itself in response to the changing external conditions so that the ground state naturally favors the topological phase. The system consists of a quantum wire formed of individual magnetic atoms placed on the surface of an ordinary s-wave superconductor. It realizes the Kitaev paradigm of topological superconductivity when the wavevector characterizing the emergent spin helix dynamically self-tunes to support the topological phase.
Coalgebras, Models and Logics for Quantum Systems
September 17, 2013

PIRSA:13090072
Quantum Physics
Coalgebras are a flexible tool commonly used in computer science to model abstract devices and systems. Coalgebraic models also come with a natural notion of logics for the systems being modelled. In this talk we will introduce coalgebras and aim to illustrate their usefulness for modelling physical systems. Extending earlier work of Abramsky, we will show how a weakening of the usual morphisms for coalgebras provides the flexibility to model quantum systems in an easy to motivate manner. We will then investigate how a natural extension to the usual notion of coalgebraic logic can be used to produce logics for reasoning about quantum systems and protocols. No prior knowledge of coalgebras will be assumed for this talk, and the emphasis throughout will be on examples rather than technical details.
Orbifolds and topological defects

Daniel Plencner Ludwig-Maximilians-Universität München (LMU)
September 17, 2013

PIRSA:13090061
High Energy Physics
Orbifolding a 2-dimensional quantum field theory by a symmetry group admits an elegant description in terms of defect lines and their junction fields. This perspective offers a natural generalization of the concept of an orbifold, in which the role of the symmetry group is replaced by a defect with the structure of a (symmetric) separable Frobenius algebra. In this talk I will focus on the case of Landau-Ginzburg models, in which defects are described by matrix factorizations. After introducing the generalized twisted sectors and discussing topological bulk and boundary correlators in these sectors, I will present a simple proof of the Cardy condition and discuss some further consistency checks on the generalized orbifold theory. This talk is based on arXiv:1307.3141 with Ilka Brunner and Nils Carqueville.
ΛCDM Large Scale Triumphs and Small Scale Challenges

Joel Primack University of California, Santa Cruz
September 17, 2013

PIRSA:13090066
Astrophysics
ΛCDM has become the standard cosmological model because its predictions agree so well with observations of the cosmic microwave background and the large-scale structure of the universe. However ΛCDM has faced challenges on smaller scales. Some of these challenges, including the “angular momentum catastrophe" and the absence of density cusps in the centers of small galaxies, may be overcome with improvements in simulation resolution and feedback. Recent simulations appear to form realistic galaxies in agreement with observed scaling relations. Although dark matter halos start small and grow by accretion, the existence of a star-forming band of halo masses naturally explains why the most massive galaxies have the oldest stars, a phenomenon known as galactic “downsizing." The discovery of many faint galaxies in the Local Group is consistent with the large number of subhalos in ΛCDM simulations. There is increasing evidence for such substructure in galaxy dark matter halos from gaps in cold stellar streams in the Milky Way and Andromeda and from gravitational lensing flux anomalies, with the prospect of rapidly increasing data on that from ALMA. The “too big to fail" (TBTF) problem is the latest apparent challenge to ΛCDM. It arose from analysis of the Aquarius and Via Lactea very-high-resolution ΛCDM simulations of Milky-Way-mass dark matter halos. Each simulated halo has ∼10 subhalos so massive and dense that they would appear to be too big to fail to form lots of stars. The TBTF problem is that none of the observed dwarf satellite galaxies of the Milky Way or Andromeda have stars moving as fast as would be expected in these densest subhalos. This may indicate the need for a more complex theory of dark matter – but several recent papers have shown that subhalos in pure dark matter simulations like Aquarius or Via Lactea are significantly modified when baryonic effects are included, so as to solve the TBTF problem. Higher resolution simulations are needed to verify this.
Edge states at domain wall junctions in supersymmetric gauge theory

Davide Gaiotto Perimeter Institute for Theoretical Physics
September 13, 2013

PIRSA:13090074
Condensed Matter
Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Donald Marolf University of California, Santa Barbara
September 12, 2013

PIRSA:13090060
General Relativity & Quantum Cosmology
A defining feature of holographic dualities is that, along with the bulk equations of motion, boundary correlators at any given time t determine those of observables deep in the bulk. We argue that this property emerges from the bulk gravitational Gauss law together with bulk quantum entanglement as embodied in the Reeh-Schlieder theorem. Stringy bulk degrees of freedom are not required and play little role even when they exist. As an example we study a toy model whose matter sector is a free scalar field. The energy density (\rho) sources what we call a pseudo-Newtonian potential (\Phi) through Poisson's equation on each constant time surface, but there is no back-reaction on the matter. We show the Hamiltonian to be essentially self-adjoint on the domain generated from the vacuum by acting with boundary observables localized in an arbitrarily small neighborhood of the chosen time t. Since the Gauss law represents the Hamiltonian as a boundary term, the model is holographic in the sense stated above.
Quantum States are Consistent Probability Distributions

Nadish de Silva University of Oxford
September 12, 2013

PIRSA:13090070
Quantum Physics
We describe a notion of state for a quantum system which is given in terms of a collection of empirically realizable probability distributions and is formally analogous to the familiar concept of state from classical statistical mechanics. We first demonstrate the mathematical equivalence of this new notion to the standard quantum notion of density matrix. We identify the simple logical consistency condition (a generalization of the familiar no-signalling condition) which a collection of distributions must obey in order to reconstruct the unique quantum state from which they arise. In this way, we achieve a formal expression of the common intuition of a quantum state as being classical distributions on compatible observables.
The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe
September 11, 2013

PIRSA:13090065
High Energy Physics
Despite being one of the most abundant constituents of the Universe and more than a half a century of study, some of the most fundamental properties of the neutrino have only been recently uncovered, and others still remain unresolved. I will discuss important developments in the phenomenon of neutrino oscillations, a transmutation process that allows neutrinos to change between three types as they propagate in time. In particular, recent discoveries have opened up the possibility of CP violation in neutrino oscillations, asymmetries in the behavior of neutrinos and their anti-matter counterparts. CP violation, along with other unresolved properties of the neutrino, may play a central role in how the universe came to a matter-dominated state. I will also discuss a new generation of experiments that may allow us to establish whether CP violation does indeed occur in neutrino oscillations.
Quantum Observables as Real-valued Functions and Quantum Probability
September 10, 2013

PIRSA:13090068
Quantum Physics
Quantum observables are commonly described by self-adjoint operators on a Hilbert space H. I will show that one can equivalently describe observables by real-valued functions on the set P(H) of projections, which we call q-observable functions. If one regards a quantum observable as a random variable, the corresponding q-observable function can be understood as a quantum quantile function, generalising the classical notion. I will briefly sketch how q-observable functions relate to the topos approach to quantum theory and the process called daseinisation. The topos approach provides a generalised state space for quantum systems that serves as a joint sample space for all quantum observables. This is joint work with Barry Dewitt.
From dlogs to dilogs

Arthur Lipstein Durham University
September 10, 2013

PIRSA:13090049
High Energy Physics
In this talk, I will describe a new form of hidden simplicity in the planar scattering amplitudes of N=4 super-Yang-Mills theory, notably that the loop integrands can be expressed in dlog form. I will explain how this form arises geometrically from computing the scattering amplitudes using a holomorphic Wilson loop in twistor space. I will also describe a systematic method for evaluating such integrals and use it to obtain a new formula for the 1-loop MHV amplitude. These techniques can be extended to higher loop amplitudes and may lead to a simple and efficient method for computing scattering amplitudes more generally.

Title	Speaker(s)	Date	Talk Type	Info link
The World is Discrete	Olaf Dreyer	2013-09-19	Scientific Series	View details
Short Gamma-Ray Bursts and the Electromagnetic Counterparts of Gravitational Wave Sources	Edo Berger	2013-09-18	Scientific Series	View details
Self-organized topological state with Majorana fermions	Marcel Franz	2013-09-17	Scientific Series	View details
Coalgebras, Models and Logics for Quantum Systems		2013-09-17	Scientific Series	View details
Orbifolds and topological defects	Daniel Plencner	2013-09-17	Scientific Series	View details
ΛCDM Large Scale Triumphs and Small Scale Challenges	Joel Primack	2013-09-17	Scientific Series	View details
Edge states at domain wall junctions in supersymmetric gauge theory	Davide Gaiotto	2013-09-13	Scientific Series	View details
Holography without Strings - Joint Quantum Gravity and String Theory Seminar	Donald Marolf	2013-09-12	Scientific Series	View details
Quantum States are Consistent Probability Distributions	Nadish de Silva	2013-09-12	Scientific Series	View details
The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe		2013-09-11	Scientific Series	View details
Quantum Observables as Real-valued Functions and Quantum Probability		2013-09-10	Scientific Series	View details
From dlogs to dilogs	Arthur Lipstein	2013-09-10	Scientific Series	View details

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Format results

The World is Discrete

Short Gamma-Ray Bursts and the Electromagnetic Counterparts of Gravitational Wave Sources

Self-organized topological state with Majorana fermions

Coalgebras, Models and Logics for Quantum Systems

Orbifolds and topological defects

ΛCDM Large Scale Triumphs and Small Scale Challenges

Edge states at domain wall junctions in supersymmetric gauge theory

Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Quantum States are Consistent Probability Distributions

The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe

Quantum Observables as Real-valued Functions and Quantum Probability

From dlogs to dilogs

The World is Discrete

Short Gamma-Ray Bursts and the Electromagnetic Counterparts of Gravitational Wave Sources

Self-organized topological state with Majorana fermions

Coalgebras, Models and Logics for Quantum Systems

Orbifolds and topological defects

ΛCDM Large Scale Triumphs and Small Scale Challenges

Edge states at domain wall junctions in supersymmetric gauge theory

Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Quantum States are Consistent Probability Distributions

The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe

Quantum Observables as Real-valued Functions and Quantum Probability

From dlogs to dilogs