Scientific Series

Displaying 3265 - 3276 of 5012

Plasma without Plasma: Exploring Force-Free Magnetospheres

Sam Gralla
University of Arizona
October 10, 2013

PIRSA:13100078
Strong Gravity
Einstein and the Fugu

Andrew Waldron
University of California, Davis
October 10, 2013

PIRSA:13100101
Cosmology
From Supersolidity to Giant Plasticity: Defects in Quantum Crystals

John Beamish
University of Alberta
October 09, 2013

PIRSA:13100065
Condensed Matter
A Nearly Gaussian Hubble-patch in a non-Gaussian Universe

Marilena LoVerde
University of Washington
October 08, 2013

PIRSA:13100076
Cosmology
Geometry and Topology in the Fractional Quantum Hall Effect

Duncan Haldane
Princeton University
October 07, 2013

PIRSA:13100086
Condensed Matter
Alan Turing and the Enigma Machine

James Grime
University of Cambridge

October 02, 2013

PIRSA:13100079
Universal fault-tolerant quantum computation with only transversal gates and error correction

Adam Paetznick
September 25, 2013

PIRSA:13090069
Quantum Foundations
Slippery Waves: Brilliance Brings Blind Spots

Leo Kadanoff
September 25, 2013

PIRSA:13090051
Mathematical physics
Electroweak Cogenesis and a CP Violating Higgs Boson
September 24, 2013

PIRSA:13090077
Particle Physics
Not so random walks in cosmology

Ravi Sheth
University of Pennsylvania
September 24, 2013

PIRSA:13090063
Cosmology
The World is Discrete

Olaf Dreyer
Freelance Consultant
September 19, 2013

PIRSA:13090073
Quantum Gravity
Short Gamma-Ray Bursts and the Electromagnetic Counterparts of Gravitational Wave Sources

Edo Berger
Harvard University

September 18, 2013

PIRSA:13090050

Plasma without Plasma: Exploring Force-Free Magnetospheres

Sam Gralla
University of Arizona
October 10, 2013

PIRSA:13100078
Strong Gravity
Pulsars have enormous magnetic fields whose energy density dwarfs the rest mass density of their plasma magnetosphere. In this regime of a plasma, the particles drop out of the description, leaving a set of equations for the electromagnetic field alone. This non-linear, deterministic system is known as force-free electrodynamics, and turns out to have some beautiful and bizarre features. I will give a pedagogical introduction to these equations and their role in astrophysics and then discuss our recent contributions. We have taken a geometric viewpoint, using the null structure of spacetime to unify previous exact solutions and discover new ones. We have found non-stationary, non-axisymmetric solutions that describe the outer magnetosphere of pulsars, including those that are accelerated or torqued. We have derived the standard cartoon of the aligned pulsar magnetosphere from an explicit, minimal set of assumptions. Time permitting, I will also discuss some properties of black hole magnetospheres: Blandford-Znajek energy extraction, non-scattering force-free waves, and the no-ingrown-hair theorem.
Einstein and the Fugu

Andrew Waldron
University of California, Davis
October 10, 2013

PIRSA:13100101
Cosmology
From Supersolidity to Giant Plasticity: Defects in Quantum Crystals

John Beamish
University of Alberta
October 09, 2013

PIRSA:13100065
Condensed Matter
In 2004, Kim and Chan reported torsional oscillator experiments on 4He crystals which showed evidence of “non-classical rotational inertia”, the mass decoupling expected for a long-sought “supersolid” state. It soon became clear that this behavior is not a property of perfect crystals – defects are involved. In 2007, we made elastic measurements which showed, to our surprise, that the shear modulus of solid 4He increases dramatically below 0.2 K, with the same dependence on temperature, amplitude and 3He impurity concentration as the torsional oscillator anomaly. These shear modulus changes are due to dislocations and their interactions with impurities and vacancies. Our experiments raised an obvious question – could the torsional oscillator behavior be an artifact of the elastic changes, rather than evidence of supersolidity? During the past two years it has become clear that the answer is “yes” and interest has focused on the properties of dislocations in a quantum solid like 4He. By growing high quality single crystals in optical cells, we have now been able to explore the behavior of dislocations in 4He in unprecedented detail. In some crystals the dislocations reduce the shear modulus by more than 80%, an extraordinary effect we describe as “giant plasticity”. Solid helium has proved to be an ideal system in which to do materials science, as well as to address fundamental questions about quantum solids.
A Nearly Gaussian Hubble-patch in a non-Gaussian Universe

Marilena LoVerde
University of Washington
October 08, 2013

PIRSA:13100076
Cosmology
Local-type primordial non-Gaussianity couples statistics of the curvature perturbation \zeta on vastly different physical scales. Because of this coupling, statistics (i.e. the polyspectra) of \zeta in our Hubble volume may not be representative of those in the larger universe -- that is, they may be biased. The bias depends on the local background value of \zeta, which includes contributions from all modes with wavelength k ~< H_0 and is therefore enhanced if the entire post-inflationary patch is large compared with our Hubble volume. I will discuss the bias to locally-measured statistics for general local-type non-Gaussianity. I will discuss three examples in detail: (i) the usual fNL, gNL model, (ii) a strongly non-Gaussian model with \zeta ~ \zeta_G^p, and (iii) two-field non-Gaussian initial conditions. In each scenario one may generate statistics in a Hubble-size patch that are weakly Gaussian and consistent with observations despite the fact that the statistics in the larger, post-inflationary patch look very different. Finally, I will present a worked example of how the variation in local statistics arises in the curvaton scenario.
Geometry and Topology in the Fractional Quantum Hall Effect

Duncan Haldane
Princeton University
October 07, 2013

PIRSA:13100086
Condensed Matter
The FQHE is exhibited by electrons moving on a 2D surface through which a magnetic flux passes, giving rise to flat bands with extensive degeneracy (Landau levels). The degeneracy of a partially-filled Landau level is lifted by Coulomb repulsion between the electrons, which at certain rational fillings, leads to gapped incompressible topologically-ordered fluid states exhibiting the FQHE. Successful model wavefunctions for FQHE states, such as the Laughlin and Moore-Read states, are surprisingly related to Euclidean conformal field theory, even though they are gapped incompressiible quantum fluids with a fundamental unit of area set by the area per magnetic flux quantum h/e. The model wavefunctions are parametrized by a continuously-variable Euclidean metric, just like the Euclidean conformal group of the cft to which they are related. This metric is fixed locally both by the form of the projected Coulomb interaction within the partially-filled Landau level, and by local gradients of the tangential electric field on the 2D surface, promoting it from a static flat metric fixed globally by the cft, to a dynamic local physical degree of freedom of the FQHE fluid with area-preserving zero-point fluctuations that leave an imprint in the ground-state structure function. The curious connection to cft appears to be that the Virasoro algebra plays a fundament role in both cft and FQHE, for apparently-unrelated reasons. In the FQHE it derives from a chiral "gravitional" (geometric) topologically-protected anomaly at the edge of the fluid that is also revealed in the entanglement spectrum of a cut through the bulk fluid.
Alan Turing and the Enigma Machine

James Grime
University of Cambridge

October 02, 2013

PIRSA:13100079

Alan Turing was one of our great 20th century mathematicians, and a pioneer of computer science. However, he may best be remembered as one of the leading code breakers of Bletchley Park during World War II. It was Turing's brilliant insights and mathematical mind that helped to break Enigma, the apparently unbreakable code used by the German military. We present a history of both Alan Turing and the Enigma, leading up to this fascinating battle of man against machine - including a full demonstration of an original WWII Enigma Machine!
Universal fault-tolerant quantum computation with only transversal gates and error correction

Adam Paetznick
September 25, 2013

PIRSA:13090069
Quantum Foundations
Transversal implementations of encoded unitary gates are highly desirable for fault-tolerant quantum computation. It is known, however, that transversal gates alone cannot be computationally universal. I will show that the limitation on universality can be circumvented using only fault-tolerant error correction, which is already required anyway. This result applies to ``triorthogonal'' stabilizer codes, which were recently introduced by Bravyi and Haah for state distillation. I will show that triothogonal codes admit transversal implementation of the controlled-controlled-Z gate, and then demonstrate a transversal Hadamard construction which uses error correction to preserve the codespace. I will also discuss how to adapt the distillation procedure of Bravyi and Haah to Toffoli gates, improving on existing Toffoli distillation schemes.
Slippery Waves: Brilliance Brings Blind Spots

Leo Kadanoff
September 25, 2013

PIRSA:13090051
Mathematical physics
Superfluidity and superconductivity are two remarkable phenomena in which, at low temperatures, materials abruptly gain the ability to flow without friction. Microscopic quantum theories of these phases of matter were constructed in blockbuster papers of Lev Landau (1940) and John Bardeen, Leon Cooper, and J. Robert Schrieffer (1957). The actual explanation of the flow, however, is rooted in a Einstein paper of 1924 that introduces a condensate, a quantum configuration describing a finite fraction of the particles in the system. Superfluidity can then be understood in terms of the wave function for this configuration, which necessarily extends over a finite fraction of the system. Neither blockbuster paper mentions Einstein or the crucial idea of a condensate wave function. The reasons for this omission are mooted.
Electroweak Cogenesis and a CP Violating Higgs Boson
September 24, 2013

PIRSA:13090077
Particle Physics
We propose a simple renormalizable model of baryogenesis and asymmetric dark matter generation at the electroweak phase transition. Our setup utilizes the two Higgs doublet model plus two complex gauge singlets, the lighter of which is stable dark matter. The dark matter is charged under a global symmetry that is broken in the early universe but restored during the electroweak phase transition. Because the ratio of baryon and dark matter asymmetries is controlled by model parameters, the dark matter need not be light. Thus, new force carriers are unnecessary and the symmetric dark matter abundance can be eliminated via Higgs portal interactions alone. The dark matter mass is also constrained within a window around the weak scale. One of the main predictions of this model is CP violating Higgs signals at the LHC and future colliders.
Not so random walks in cosmology

Ravi Sheth
University of Pennsylvania
September 24, 2013

PIRSA:13090063
Cosmology
I'll discuss a number of insights into the process of nonlinear structure formation which come from the study of random walks crossing a suitably chosen barrier. These derive from a number of new results about walks with correlated steps, and include a unified framework for the peaks and excursion set frameworks for estimating halo abundances, evolution and clustering, as well as nonlinear, nonlocal and stochastic halo bias, all of which matter for the next generation of large scale structure datasets.
The World is Discrete

Olaf Dreyer
Freelance Consultant
September 19, 2013

PIRSA:13090073
Quantum Gravity
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.

Title	Speaker(s)	Date	Talk Type	Info link
Plasma without Plasma: Exploring Force-Free Magnetospheres	Sam Gralla	2013-10-10	Scientific Series	View details
Einstein and the Fugu	Andrew Waldron	2013-10-10	Scientific Series	View details
From Supersolidity to Giant Plasticity: Defects in Quantum Crystals	John Beamish	2013-10-09	Scientific Series	View details
A Nearly Gaussian Hubble-patch in a non-Gaussian Universe	Marilena LoVerde	2013-10-08	Scientific Series	View details
Geometry and Topology in the Fractional Quantum Hall Effect	Duncan Haldane	2013-10-07	Scientific Series	View details
Alan Turing and the Enigma Machine	James Grime	2013-10-02	Scientific Series	View details
Universal fault-tolerant quantum computation with only transversal gates and error correction	Adam Paetznick	2013-09-25	Scientific Series	View details
Slippery Waves: Brilliance Brings Blind Spots	Leo Kadanoff	2013-09-25	Scientific Series	View details
Electroweak Cogenesis and a CP Violating Higgs Boson		2013-09-24	Scientific Series	View details
Not so random walks in cosmology	Ravi Sheth	2013-09-24	Scientific Series	View details
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

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