Strong Gravity

298 talks

S020

Collection Type Series

Description This series consists of talks in the area of Quantum Gravity.

Displaying 217 - 228 of 298

Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space

Andrew Strominger Harvard University
March 13, 2014
PIRSA:14030087
Strong Gravity
Sequestering Lorentz violation in the Lifshitz sector

Maxim Pospelov University of Minnesota
March 06, 2014
PIRSA:14030092
Strong Gravity
On null singularities in general relativity

Mihalis Dafermos Princeton University
February 13, 2014
PIRSA:14020133
Strong Gravity
The Radius of Neutron Stars and the Dense Matter Equation of State

Robert Rutledge McGill University
February 06, 2014
PIRSA:14020087
Strong Gravity
Collisions in AdS and the thermalisation of heavy-ion collisions

Wilke van der Schee European Organization for Nuclear Research (CERN)
November 28, 2013
PIRSA:13110089
Strong Gravity
Charged particle motion in magnetized black holes

Valeri Frolov University of Alberta
November 21, 2013
PIRSA:13110066
Strong Gravity
Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Marc Casals Universität Leipzig
November 14, 2013
PIRSA:13110067
Strong Gravity
Dynamical Emergence of Universal Horizons during the formation of Black Holes

Mehdi Saravani Goldman Sachs (United States)
November 07, 2013
PIRSA:13110087
Strong Gravity
New lessons about hydrodynamics from gravity

Michal Heller Ghent University
October 31, 2013
PIRSA:13100064
Strong Gravity
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
Strong Gravity
Plasma without Plasma: Exploring Force-Free Magnetospheres

Sam Gralla University of Arizona
October 10, 2013
PIRSA:13100078
Strong Gravity
Neutron Stars and the Dense Matter Equation of State

Madappa Prakash Ohio University
August 08, 2013
PIRSA:13080000
Strong Gravity

Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space

Andrew Strominger Harvard University
March 13, 2014
PIRSA:14030087
Strong Gravity
We argue that the infinite-dimensional BMS symmetry discovered by Bondi et. al in the 60s provides an exact symmetry of the quantum gravity S-matrix. The Ward identity of this symmetry is shown to be precisely Weinberg's soft graviton theorem, also discovered in the 60s. A parallel infinite-dimensional symmetry is found to be generated in nonabelian gauge theories by gauge transformations which go to an angle-dependent finite constant at null infinity. The Ward identity of this symmetry is shown to be the soft gluon theorem.
Sequestering Lorentz violation in the Lifshitz sector

Maxim Pospelov University of Minnesota
March 06, 2014
PIRSA:14030092
Strong Gravity
Horava's proposal to use Lifshitz propagators for gravitons above certain energy scales may provide a viable theory of quantum gravity without further need of UV completion. In my talk, I will address the question of whether the complete lack of Lorentz invariance above a certain energy scale is a big problem for any realistic construction. I will argue that it is not, provided that the onset of Lifshitz scaling for gravitons occurs at momentum scale much lower than the Planck mass. I will also discuss consequences of combining Lifshitz gravity and supersymmetric matter sector.
On null singularities in general relativity

Mihalis Dafermos Princeton University
February 13, 2014
PIRSA:14020133
Strong Gravity
This talk will discuss the formation, structure and interaction of null singularities for
the Einstein equations, as well as what this all means for the singular boundary
of generic space times within black hole regions.
The Radius of Neutron Stars and the Dense Matter Equation of State

Robert Rutledge McGill University
February 06, 2014
PIRSA:14020087
Strong Gravity
The equation of state of matter at and above nuclear densities remains a major theoretically uncertain prediction of QCD. Observations of the mass-radius relationship of neutron stars constrain, and can directly measure, the dense matter equation of state. I will discuss how measurements of neutron star radii have already constrained the dEOS, and how future work will directly measure the dEOS, providing an important constraint on models of the strong force.
Collisions in AdS and the thermalisation of heavy-ion collisions

Wilke van der Schee European Organization for Nuclear Research (CERN)
November 28, 2013
PIRSA:13110089
Strong Gravity
The motivation of this seminar is to understand the thermalisation of heavy ion collisions using AdS/CFT. These collisions can be modelled as colliding planar gravitational shock waves. This gives rise to rich and interesting dynamics; wide shocks come to a full stop and expand hydrodynamically, as was previously found by Chesler and Yaffe. High energy collisions (corresponding to thin shocks) pass through each other, after which a plasma forms in the middle, within a proper time 1/T, with T the local temperature at that time. After this I will discuss recent results where we studied the influence of microscopic structure in the longitudinal direction of the shock waves, and thereby found a coherent regime. This has implications for both fluctuations in nucleus-nucleus collisions, and for recent proton-lead collisions at at LHC. The final part will cover a radially expanding calculation, where some simplifications allowed us to solve the model all the way till the final particle spectra, with an interesting comparison with experimental data.
Charged particle motion in magnetized black holes

Valeri Frolov University of Alberta
November 21, 2013
PIRSA:13110066
Strong Gravity
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.
Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Marc Casals Universität Leipzig
November 14, 2013
PIRSA:13110067
Strong Gravity
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.
Dynamical Emergence of Universal Horizons during the formation of Black Holes

Mehdi Saravani Goldman Sachs (United States)
November 07, 2013
PIRSA:13110087
Strong Gravity
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].
New lessons about hydrodynamics from gravity

Michal Heller Ghent University
October 31, 2013
PIRSA:13100064
Strong Gravity
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.
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
Strong Gravity
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.
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.
Neutron Stars and the Dense Matter Equation of State

Madappa Prakash Ohio University
August 08, 2013
PIRSA:13080000
Strong Gravity
Implications of recently well-measured neutron star masses, particularly near and above 2 solar masses, for the equation of state (EOS) of neutron star matter will be highlighted. Model independent upper limits to thermodynamic properties in neutron stars, which only depend on the neutron star maximum mass, established from causality considerations will be presented. The need for non-perturbative treatments of quark matter in neutron stars is revealed through studies of self-bound quark matter stars, and of nucleon-quark hybrid stars. The extent to which several well-measured masses and radii of individual neutron stars can establish a model-independent EOS through an inversion of the stellar structure equations will be briefly discussed.

Title	Speaker(s)	Date	Talk Type	Info
Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space	Andrew Strominger	2014-03-13	Scientific Series	View details
Sequestering Lorentz violation in the Lifshitz sector	Maxim Pospelov	2014-03-06	Scientific Series	View details
On null singularities in general relativity	Mihalis Dafermos	2014-02-13	Scientific Series	View details
The Radius of Neutron Stars and the Dense Matter Equation of State	Robert Rutledge	2014-02-06	Scientific Series	View details
Collisions in AdS and the thermalisation of heavy-ion collisions	Wilke van der Schee	2013-11-28	Scientific Series	View details
Charged particle motion in magnetized black holes	Valeri Frolov	2013-11-21	Scientific Series	View details
Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut	Marc Casals	2013-11-14	Scientific Series	View details
Dynamical Emergence of Universal Horizons during the formation of Black Holes	Mehdi Saravani	2013-11-07	Scientific Series	View details
New lessons about hydrodynamics from gravity	Michal Heller	2013-10-31	Scientific Series	View details
Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars	Aaron Zimmerman	2013-10-17	Scientific Series	View details
Plasma without Plasma: Exploring Force-Free Magnetospheres	Sam Gralla	2013-10-10	Scientific Series	View details
Neutron Stars and the Dense Matter Equation of State	Madappa Prakash	2013-08-08	Scientific Series	View details

Strong Gravity

Format results