Scientific Series

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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 Foundations
Orbifolds and topological defects

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

PIRSA:13090061
Quantum Fields and Strings
ΛCDM Large Scale Triumphs and Small Scale Challenges

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

PIRSA:13090066
Cosmology
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
Quantum Gravity
Quantum States are Consistent Probability Distributions

Nadish de Silva
University of Oxford
September 12, 2013

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

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

PIRSA:13090068
Quantum Foundations
From dlogs to dilogs

Arthur Lipstein
Durham University
September 10, 2013

PIRSA:13090049
Quantum Fields and Strings
The local Callan-Symanzik equation: structure and applications

Boaz Keren-Zur
L'Ecole Polytechnique Federale de Lausanne (EPFL)
September 06, 2013

PIRSA:13090067
Particle Physics
A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?
- Niayesh Afshordi
  University of Waterloo
- Elizabeth Gould
  Arthur B. McDonald Canadian Astroparticle Physics Research Institute
September 03, 2013

PIRSA:13090064
Quantum Foundations

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 Foundations
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-Universitiät München (LMU)
September 17, 2013

PIRSA:13090061
Quantum Fields and Strings
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
Cosmology
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
Quantum Gravity
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 Foundations
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
Particle 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 Foundations
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
Quantum Fields and Strings
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.
The local Callan-Symanzik equation: structure and applications

Boaz Keren-Zur
L'Ecole Polytechnique Federale de Lausanne (EPFL)
September 06, 2013

PIRSA:13090067
Particle Physics
The local Callan-Symanzik equation describes the response of a quantum field theory to local scale transformations in the presence of background sources. The consistency conditions associated with this anomalous equation can be used to derive powerful constraints on RG flows. We will discuss various aspects of the equation and present new results regarding the structure of the anomaly. We then use the equation to write correlation functions of the trace of the energy-momentum tensor off-criticality.
A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?
- Niayesh Afshordi
  University of Waterloo
- Elizabeth Gould
  Arthur B. McDonald Canadian Astroparticle Physics Research Institute
September 03, 2013

PIRSA:13090064
Quantum Foundations
A century after the advent of Quantum Mechanics and General Relativity, both theories enjoy incredible empirical success, constituting the cornerstones of modern physics. Yet, paradoxically, they suffer from deep-rooted, so-far intractable, conflicts. Motivations for violations of the notion of
relativistic locality include the Bell's inequalities for hidden variable theories, the cosmological horizon problem, and Lorentz-violating approaches to quantum geometrodynamics, such as Horava-Lifshitz gravity. Here, we explore a recent proposal for a ``real ensemble'' non-local description of quantum mechanics, in which ``particles'' can copy each others' observables AND phases, independent of their spatial separation. We first specify the exact theory, ensuring that it is consistent and has (ordinary) quantum mechanics as a fixed point, where all particles with the same observables have the same phases. We then study the stability of this fixed point numerically, and analytically, for simple models. We provide evidence that most systems (in our study) are locally stable to small deviations from quantum mechanics, and furthermore, the phase variance per observable, as well as systematic deviations from quantum mechanics, decay as ~ (EnergyXTime)^{-n}, where n > 2. Interestingly, this convergence is controlled by the absolute value of energy (and not energy difference). Finally, we discuss different issues related to this theory, as well as potential implications for early universe, and the cosmological constant problem.

Title	Speaker(s)	Date	Talk Type	Info link
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
The local Callan-Symanzik equation: structure and applications	Boaz Keren-Zur	2013-09-06	Scientific Series	View details
A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?	Niayesh Afshordi, Elizabeth Gould	2013-09-03	Scientific Series	View details

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