Search Talks

The study of super-Eddington accretion is essential to our understanding of the growth of super-massive black holes in the early universe, the accretion of tidally disrupted stars, and the nature of ultraluminous X-ray sources.  Unfortunately, this mode of accretion is particularly difficult to model because of the multidimensionality of the flow, the importance magnetohydrodynamic turbulence, and the dominant dynamical role played by radiation forces.  However, recent increases in computing power and advances in algorithms are facilitating major improvements in our ability to model radiation in numerical simulations of astrophysical plasmas.  I will briefly describe our new radiation transfer modules and discuss our efforts to model super-Eddington accretion flows around stellar mass and supermassive black holes.  I will focus on applications to ultraluminous X-ray sources, which must be radiating well above their Eddington luminosity unless they harbour intermediate mass black holes. I will argue that most of these sources can be (and likely are) "normal" ~10 solar mass black holes accreting and radiating with luminosities well above their Eddington "limit”.

Composite Quantum Systems - Examples and basic mathematical properties; Entanglement - Schmidt decomposition/Schmidt number; Infinite dimensional Hilbert space and unbounded operators - Dirac's approach vs von Neumann's approach. 

Causal set quantum gravity, computational methods Series

The Cactus High Performance Computing (HPC) Framework was designed to
facilitate the development of software to simulate astrophysically realistic
inspiral and merger of binary black holes and neutron stars.  A major part of the motivation for
its design was the US Binary Black Hole Grand Challenge in the 1990s, which
was an alliance of hundreds of scientists, all attempting to collaborate on
the same code base.  In order to handle such a large, diverse collaboration,
the design ended up being extremely general and versatile, able to support
virtually any sort of scientific computation.

I have developed an extensive software suite within the Cactus Framework for
doing large scale computations in discrete quantum gravity, using Causal Sets,
and also spin networks in Loop Quantum Gravity.  Recently, evidence is
emerging that ideas from discrete quantum gravity, and consequently this
software, may have much broader application in areas of Data Science,
including social science, computational neuroscience, and drug design.

The 21cm transition of atomic hydrogen is rapidly becoming one of our most powerful tools for probing the evolution of the universe.  The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a planned 1,024-element array to be built in South Africa that will study the (possible) evolution of dark energy from z=0.8 to 2.5. Its design also makes it an excellent pulsar and fast radio burst (FRB) search machine.  While the FRB rates in the HIRAX band are uncertain, we expect it will discover dozen(s) per day.  HIRAX will use inexpensive 6m satellite television-class dishes.  The same dishes can be used to build relatively inexpensive outrigger stations in southern Africa to localize a large fraction of the FRBs discovered by HIRAX to ~0.1 arcseconds, potentially transforming them into probes of the universe.

Meaning of labels; state up-date rule as a consequence of postulates; state up-date rule classically - Kochen-Specker model of qubit. Some additional references on the Kochen Specker model: Part II; Chap. D part 3.

Open question for deriving Quantum vs Classical Mechanics; 2-level systems ("Quantum Bit") - Quantum vs Classical rotations; State update rule - Luder's Rule (post-selected scenario vs non-post-selected scenario).

The era of gravitational wave detection is upon us.  Advanced LIGO (aLIGO) is now in full operation.  It has successfully detected the gravitational waves emitted from distant pairs of black holes (BHs) as they spiral together and merge.  And we have many more detections to look forward to.  But where are these BH-BH mergers happening, in the vast wilderness of the cosmos?  

One of the preferred candidates are globular clusters, massive systems of very old stars densely packed together and bound together by gravity.  Globular clusters are factories for black hole binary mergers. But we are only able to observe these factories in operation now. In order to understand how they were built and the treasures they should be expected to produce at present, we must somehow rewind their evolution over billions of years to say something about the initial conditions. Only then will we be able to understand how these beasts birth BH binaries, and are contributing to the gravitational waves currently being observed by aLIGO. After a brief overview of the concept of chaos, I will discuss recent progress in advancing our understanding of the origins of BH-BH mergers.