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Search results in General Relativity & Quantum Cosmology from PIRSA

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Charged particle motion in magnetized black holes

Valeri Frolov University of Alberta
November 21, 2013

PIRSA:13110066
General Relativity & Quantum Cosmology
Finite regions, spherical entanglement, and quantum gravity

Hal Haggard Bard College
November 14, 2013

PIRSA:13110049
General Relativity & Quantum Cosmology
Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Marc Casals Universität Leipzig
November 14, 2013

PIRSA:13110067
General Relativity & Quantum Cosmology
Matter matters in asymptotically safe quantum gravity
November 07, 2013

PIRSA:13110048
General Relativity & Quantum Cosmology
Dynamical Emergence of Universal Horizons during the formation of Black Holes

Mehdi Saravani Goldman Sachs (United States)
November 07, 2013

PIRSA:13110087
General Relativity & Quantum Cosmology
Staring into the Abyss

Avery Broderick University of Waterloo
November 06, 2013

PIRSA:13110064
Astrophysics

General Relativity & Quantum Cosmology
A causal set action

Lisa Glaser University of Vienna
October 31, 2013

PIRSA:13100063
General Relativity & Quantum Cosmology
New lessons about hydrodynamics from gravity

Michal Heller Ghent University
October 31, 2013

PIRSA:13100064
General Relativity & Quantum Cosmology
Asymptotically safe matrix models

Tim Koslowski Technical University of Applied Sciences Würzburg-Schweinfurt
October 24, 2013

PIRSA:13100067
General Relativity & Quantum Cosmology
Constructing theories from duality: my response to John Wheeler
October 17, 2013

PIRSA:13100072
General Relativity & Quantum Cosmology
Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars

Aaron Zimmerman The University of Texas at Austin
October 17, 2013

PIRSA:13100096
General Relativity & Quantum Cosmology
Superselection Sectors in AdS/CFT - Joint Quantum Gravity and String Theory Seminar

Aron Wall University of Cambridge
October 10, 2013

PIRSA:13100066
General Relativity & Quantum Cosmology

Charged particle motion in magnetized black holes

Valeri Frolov University of Alberta
November 21, 2013

PIRSA:13110066
General Relativity & Quantum Cosmology
There exist evidences that magnetic field in the vicinity of astrophysical black holes plays an important role. In particular it is required for explanation of such phenomenon as jet formation. Study of such problems in all their complexity requires 3D numerical simulations of the magnetohydrodynamics in a strong gravitational field. Quite often when dealing with such a complicated problem it is instructive to consider first its simplifications, which can be treated either analytically, or by integrating ordinary differential equations. Motion of a charged particle in a weakly magnetized black hole is an important example. We consider a non-rotating black hole in the weak magnetic field which is homogeneous at infinity. In the talk I discuss the following problems: How does such a magnetic field affect charged particle motion in the equatorial plane? How does it change the radius of the innermost stable circular orbits (ISCO) and period of rotation? I shall demonstratethat the magnetic field increases the efficiency of the energy extraction from the black hole and that magnetized black holes can be used as "particle accelerators". Finally, I shall discuss out-of-equatorial-plane motion and demonstrate that it is chaotic. Possible applications of these results to astrophysics are briefly discussed.
Finite regions, spherical entanglement, and quantum gravity

Hal Haggard Bard College
November 14, 2013

PIRSA:13110049
General Relativity & Quantum Cosmology
An exciting frontier in physics is to understand the quantum nature of gravitation in finite regions of spacetime. Study of these regions from ``below'', that is, by studying the quantum geometry of finite regions emerging from loop gravity and spin networks has recently resulted in a new road to the quantization of volume and to evidence that there is a robust gap in the volume spectrum. In this talk I will complement these results with recent work on conformal field theories in a particular finite region, a spherical ball of space. This new view afforded from ``above" gives insights into entanglement and the Reeh-Schlieder theorem, allows calculation of the entanglement spectrum, and suggests a new route to constructing the Minkowski vacuum out of independent finite regions in quantum gravity.
Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Marc Casals Universität Leipzig
November 14, 2013

PIRSA:13110067
General Relativity & Quantum Cosmology
The modelling of gravitational wave sources is of timely interest given the exciting prospect of a first detection of gravitational waves by the new generation of detectors. The motion of a small compact object around a massive black hole deviates from a geodesic due to the action of its own field, giving rise to a self-force and the emission of gravitational waves. The self-force program has recently achieved important results using well-established methods. In this talk, we will present a different, novel method, where the self-force is calculated via the Green function of the wave equation that the field perturbation satisfies. We will present a calculation of the global Green function on Schwarzschild black hole spacetime. The calculation is carried out via a spectroscopy analysis of the Green function, which includes quasinormal modes and a branch cut in the complex-frequency plane. We will apply this analysis to calculate the self-force on a scalar charge and to reveal geometrical properties of wave propagation on a Schwarzschild background.
Matter matters in asymptotically safe quantum gravity
November 07, 2013

PIRSA:13110048
General Relativity & Quantum Cosmology
The Functional Renormalisation Group technique has received great attention in recent times proving itself as a powerful tool to describe the high energy behaviour of gravitational interactions.
Its key ingredient is a nontrivial fixed point of the theory renormalization group flow which controls the behavior of the coupling constants in the ultraviolet regime and ensures that physical quantities are safe from divergences. I will briefly review the main ingredients of the gravitational asymptotic safety framework before focusing on the effect of massless minimally coupled scalars, fermions and vector fields on the gravitational fixed point. I will then set bounds on the type and number of such fields requiring the existence of a UV attractive fixed point. I will also discuss the dynamically generated quantum-gravity scale in asymptotic safety, which is the transition scale to the fixed-point regime, and its variation as a function of matter degrees of freedom. To conclude I will also consider the case of higher dimensional models.
Dynamical Emergence of Universal Horizons during the formation of Black Holes

Mehdi Saravani Goldman Sachs (United States)
November 07, 2013

PIRSA:13110087
General Relativity & Quantum Cosmology
In many theories with fundamental preferred frame, such as Einstein-Aether or Gravitational Aether theories, K-essence, Cuscuton theory, Shape Dynamics, or (non-projectable) Horava-Lifshitz gravity, the low energy theory contains a fluid with superluminal or incompressible excitations. In this talk, I study the formation of black holes in the presence of such a fluid. In particular, I focus on the incompressible limit of the fluid (or Constant Mean Curvature foliation) in the space-time of a spherically collapsing shell within an asymptotically cosmological space-time. In this case, I show that an observer inside 3/4 of the Schwarzschild radius cannot send a signal outside, after a stage in collapse, even using signals that propagate infinitely fast in the preferred frame. This confirms the dynamical emergence of universal horizons that have been previously found in static solutions [arXiv:1110.2195, arXiv:1104.2889, arXiv:1212.1334].
Staring into the Abyss

Avery Broderick University of Waterloo
November 06, 2013

PIRSA:13110064
Astrophysics

General Relativity & Quantum Cosmology
Nearly a century after their discovery, black holes remain one of the most striking, and problematic predictions of general relativity. Even more unsettling is the fact that they actually appear to exist! With only a handful of exceptions, every galaxy contains a supermassive behemoth, millions to billions as massive as the sun, at their center. These supermassive black holes are hardly incidental, they gravitationally power enormous outflows that rule the fates of their hosts. Despite the critical role they play in our understanding of gravity and impact upon the visible universe, actually testing their nature has remained beyond our reach - until now. Dr. Broderick will describe how astronomers are currently constructing (and operating) facilities that will image the horizons of black holes, and what we can already say about these enigmatic monsters in the dark.
A causal set action

Lisa Glaser University of Vienna
October 31, 2013

PIRSA:13100063
General Relativity & Quantum Cosmology
Causal set theory is discrete, fully covariant theory of quantum gravity. The discrete framework makes it necessary to reformulate continuum concepts. One of these concepts is that of a derivative operator. It is possible to define a derivative operator in causal sets that in the continuum limit agrees with the d'Alembertian for a scalar field. This operator can be used to define a causal set action, which enables Monte-Carlo simulations. In this seminar I will present this operator and action and then show some results of Monte-Carlo simulations in 2 dimensions.
New lessons about hydrodynamics from gravity

Michal Heller Ghent University
October 31, 2013

PIRSA:13100064
General Relativity & Quantum Cosmology
Hydrodynamics of relativistic plasmas received, within the last 10 years, a lot of attention. The reason for it, on one hand, is the quest for theoretical understanding of the quark-gluon plasma created in heavy ion collisions and, on the other, advances in holographic duality and black hole physics in anti-de Sitter spacetimes. I will describe recent progress in answering foundational issues in hydrodynamics of strongly coupled systems, i.e. questions about its applicability and the character of hydrodynamic gradient expansion, that was achieved with the use of numerical techniques in anti-de Sitter spacetimes in the strong gravity regime.
Asymptotically safe matrix models

Tim Koslowski Technical University of Applied Sciences Würzburg-Schweinfurt
October 24, 2013

PIRSA:13100067
General Relativity & Quantum Cosmology
The functional renormalization group is a tool in the systematic search for Euclidean QFTs that works with very little input: All one needs to specify is a field content, symmetries and a notion of locality. The functional renormalization group then allows one to scan this theory space for bare actions for which the path integral can be performed nonperturbatively. These actions appear as fixed points (and relevant deformations) of the renormalization group flow (so-called asymptotic safety). Such a systematic search has so far not been performed for the tensor model approach to quantum gravity. We investigate matrix models for 2-dimensional gravity and the Grosse-Wulkenhaar model, which is a simple tensor model for a 4D noncommutative scalar field theory, as a first step. I will report on work, done in collaboration with Astrid Eichhorn and Alessandro Sfondrini, where we confirmed asymptotic safety purely through functional RG methods. Based on the lessons learned from these models I will summarize how the usual continuum RG approach has to be generalized for the investigation of tensor models and conclude with a recipe for the investigation of general tensor models.
Constructing theories from duality: my response to John Wheeler
October 17, 2013

PIRSA:13100072
General Relativity & Quantum Cosmology
The late physicist John Wheeler, was renowned for his Socratic method of conducting physics discussions. "Why is general relativity the way it is? What makes it special?" were reportedly questions one should expect in his presence. There are different answers to these questions, each requiring a set of assumptions - which Wheeler would likely question again - and each bringing with it new insights into physics as a whole. This talk will put forward new principles for deriving general relativity. Perhaps more than is the case with other construction principles, the principles introduced are not limited to the derivation of general relativity, requiring only an specification of the theory's phase space in order to be applicable. To be less enigmatic, one defines observable equivalence between physical theories in the Dirac constraint setting, and then the principle merely searches theory space for two equivalent (or dual) fully constrained theories. We find it quite remarkable that such a complex theory as general relativity emerges, when no initial presupposition even on the existence of space-time is made. If there is time (and I will argue there is!) I will discuss another issue that also distinguishes the present set of assumptions: the possibility that they are in a concrete sense ``self-selected", which I like to think would be more satisfactory to Wheeler's line of questioning (or at least give him more to chew on).
Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars

Aaron Zimmerman The University of Texas at Austin
October 17, 2013

PIRSA:13100096
General Relativity & Quantum Cosmology
I will review recent work in two very different topics. First, I will discuss the quasinormal mode spectrum of nearly extremal Kerr black holes, where a bifurcation of the frequency spectrum is observed. In addition, collective oscillations of many modes is possible, resulting in a power-law rather than exponentially decaying ringdown. Next, I will discuss a recent proposal for how tidally induced, multimode coupling of normal modes in neutron stars can destabilize the stars. Such an instability could hamper gravitational wave detection of neutron star binaries by matched filtering. By accounting for higher-order multimode couplings, it can be shown that there is no such instability for neutron star binaries, although a milder instability may exist for binaries with less compact objects.
Superselection Sectors in AdS/CFT - Joint Quantum Gravity and String Theory Seminar

Aron Wall University of Cambridge
October 10, 2013

PIRSA:13100066
General Relativity & Quantum Cosmology
AdS/CFT is a duality relating the degrees of freedom in a D dimensional bulk gravity theory to a (D-1) dimensional theory living on the boundary. I will argue that in fact the boundary theory contains only a subset of the bulk observables. For each state of the boundary theory, there are multiple bulk states dual to it, which can be operationally distinguished by observers who fall across event horizons. Based on arXiv:1210.3590.

Title	Date	Collection	Type	Info
Charged particle motion in magnetized black holes	2013‑11‑21	Strong Gravity	Scientific Series	View details
Finite regions, spherical entanglement, and quantum gravity	2013‑11‑14	Quantum Gravity	Scientific Series	View details
Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut	2013‑11‑14	Strong Gravity	Scientific Series	View details
Matter matters in asymptotically safe quantum gravity	2013‑11‑07	Quantum Gravity	Scientific Series	View details
Dynamical Emergence of Universal Horizons during the formation of Black Holes	2013‑11‑07	Strong Gravity	Scientific Series	View details
Staring into the Abyss	2013‑11‑06	Public Lecture Series	Public Lectures	View details
A causal set action	2013‑10‑31	Quantum Gravity	Scientific Series	View details
New lessons about hydrodynamics from gravity	2013‑10‑31	Strong Gravity	Scientific Series	View details
Asymptotically safe matrix models	2013‑10‑24	Quantum Gravity	Scientific Series	View details
Constructing theories from duality: my response to John Wheeler	2013‑10‑17	Quantum Gravity	Scientific Series	View details
Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars	2013‑10‑17	Strong Gravity	Scientific Series	View details
Superselection Sectors in AdS/CFT - Joint Quantum Gravity and String Theory Seminar	2013‑10‑10	Quantum Gravity	Scientific Series	View details

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Charged particle motion in magnetized black holes

Finite regions, spherical entanglement, and quantum gravity

Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Matter matters in asymptotically safe quantum gravity

Dynamical Emergence of Universal Horizons during the formation of Black Holes

Staring into the Abyss

A causal set action

New lessons about hydrodynamics from gravity

Asymptotically safe matrix models

Constructing theories from duality: my response to John Wheeler

Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars

Superselection Sectors in AdS/CFT - Joint Quantum Gravity and String Theory Seminar

Charged particle motion in magnetized black holes

Finite regions, spherical entanglement, and quantum gravity

Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Matter matters in asymptotically safe quantum gravity

Dynamical Emergence of Universal Horizons during the formation of Black Holes

Staring into the Abyss

A causal set action

New lessons about hydrodynamics from gravity

Asymptotically safe matrix models

Constructing theories from duality: my response to John Wheeler

Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars

Superselection Sectors in AdS/CFT - Joint Quantum Gravity and String Theory Seminar