Strong Gravity

Displaying 229 - 240 of 317

A mechanism for vortex annihilation in two dimensional superfluid turbulence

Andrew Lucas University of Colorado Boulder
May 22, 2014

PIRSA:14050139
Strong Gravity
Gravity waves from Kerr/CFT

Achilleas Porfyriadis Harvard University
May 15, 2014

PIRSA:14050009
Strong Gravity
Black holes without Lorentz symmetry

Thomas Sotiriou University of Nottingham
May 08, 2014

PIRSA:14050002
Strong Gravity
Geometric inequalities for black holes

Sergio Dain Universidad Nacional de Cordoba
May 01, 2014

PIRSA:14050030
Strong Gravity
The characteristic structure of the Weyl curvature tensor and its utilization

Fan Zhang Beijing Normal University
April 24, 2014

PIRSA:14040139
Strong Gravity
Compact objects as dark-matter probes

Paolo Pani Instituto Superior Tecnico - Departamento de Física
April 17, 2014

PIRSA:14040078
Strong Gravity
Bungee jumping of black holes in AdS universe
March 27, 2014

PIRSA:14030108
Strong Gravity
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

A mechanism for vortex annihilation in two dimensional superfluid turbulence

Andrew Lucas University of Colorado Boulder
May 22, 2014

PIRSA:14050139
Strong Gravity
Recent numerical simulations [1] have suggested that two dimensional superfluid turbulence is characterized by a direct cascade of energy to small length scales, in contrast to the inverse cascade of normal fluids, where energy is transported to large length scales. This direct cascade is characterized by many vortex-antivortex annihilation events. Recent experimental work [2] on Bose-Einstein condensates appears to demonstrate qualitatively similar physics. I will discuss recent work in progress towards identifying the physical mechanism underlying this direct cascade, using techniques of effective field theory.
Gravity waves from Kerr/CFT

Achilleas Porfyriadis Harvard University
May 15, 2014

PIRSA:14050009
Strong Gravity
Astronomical observation suggests the existence of near-extreme Kerr black holes whose horizons spin at nearly the speed of light. Properties of diffeomorphisms imply that the dynamics of the high-redshift near-horizon region of near-extreme Kerr, which includes the innermost-stable-circular-orbit (ISCO), is governed by an infinite-dimensional emergent conformal symmetry. This symmetry may be exploited to analytically, rather than numerically, compute a variety of potentially observable processes. In this talk I will show how we compute and study the conformal transformation properties of the gravitational radiation emitted by an orbiting massive object in the large-redshift near-horizon region. I will also use conformal symmetry of the near-horizon region to compute the gravitational radiation produced during the plunge phase following the object's crossing of the ISCO.
Black holes without Lorentz symmetry

Thomas Sotiriou University of Nottingham
May 08, 2014

PIRSA:14050002
Strong Gravity
Our current definition of what a black hole is relies heavily on the assumption that there exists a finite maximum speed of propagation for any signal. Indeed, one is tempted to think that the notion of a black hole has no place in a world with infinitely fast signal propagation. I will use concrete examples from Lorentz-violating gravity theories to demonstrate that this naive expectation is not necessarily true.
Geometric inequalities for black holes

Sergio Dain Universidad Nacional de Cordoba
May 01, 2014

PIRSA:14050030
Strong Gravity
A geometric inequality in General Relativity relates quantities that have both a physical interpretation and a geometrical definition. It is well known that the parameters that characterize the Kerr-Newman black hole (angular momentum, charge, mass and horizon area) satisfy several important geometric inequalities. Remarkably enough, some of these inequalities also hold for dynamical black holes. This kind of inequalities, which are valid in the dynamical and strong field regime, play an important role in the characterization of the gravitational collapse. They are closed related with the cosmic censorship conjecture. Also, variants of these inequalities are valid for ordinary bodies. In this talk I will review recent results in this subject.
The characteristic structure of the Weyl curvature tensor and its utilization

Fan Zhang Beijing Normal University
April 24, 2014

PIRSA:14040139
Strong Gravity
The talk will summarize some results relating to clarifying the physical significance of the characteristic structure of the Weyl curvature tensor, and proposals for its utilization. I will begin by showing how null force-free or vacuum electrodynamic solutions experience reduced scattering by propagating along the principal null directions (GPNDs) of the spacetime, as if they were the flatter directions of the curvature tensor. Building on this observation, I will use complexified sectional curvatures to develop an analogy between the Weyl tensor and the second fundamental form of an immersed surface, and argue that, despite their name, the GPNDs are more akin to the asymptotic directions rather than the principal directions. I will also identify the ``true'' principal directions and curvatures, which has so far been under-utilized. I will then move on to propose usage for these quantities in topics related to the peeling theorem, the large scale geometry of the spacetime, the transition from the merger phase of binary black hole merger into the quasinormal mode ringdown phase, and perturbation of generic background spacetimes.
Compact objects as dark-matter probes

Paolo Pani Instituto Superior Tecnico - Departamento de Física
April 17, 2014

PIRSA:14040078
Strong Gravity
In the last few years the possibility of constraining dark matter with astrophysical observations of compact objects, such as white dwarfs, neutron stars and black holes, has been explored. The ultra-high density interior of neutron stars and the strong-curvature regions near massive black holes make these objects unique laboratories to test weakly-interacting particles. In the first part of this talk I will review some recent work on the potential of compact objects as dark-matter detectors, including the consequences of dark-matter accretion on compact stars and superradiant black-hole instabilities triggered by ultralight bosons. In the second part I will discus how observations of neutron stars can be used to constrain the dark-matter fraction in primordial black holes. In a close encounter with a neutron star, a primordial black hole can get gravitationally captured due to accretion, dynamical friction and tidal heating. Within a short time, the black hole is trapped inside the star and disrupts it by rapid accretion. The mere existence of old neutron stars limits the abundance of primordial black holes in the only mass range that was still unconstrained, thus suggesting that these objects cannot be the dominant dark matter constituent.
Bungee jumping of black holes in AdS universe
March 27, 2014

PIRSA:14030108
Strong Gravity
C-metric describes uniformly accelerated black holes. We will review a global structure of these solutions especially in Lambda<0 context. It turns out that for an acceleration larger than the cosmological one the metric describes pairs of black holes "bungee jumping" into spacetime from AdS infinity.
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.

Title	Speaker(s)	Date	Talk Type	Info
A mechanism for vortex annihilation in two dimensional superfluid turbulence	Andrew Lucas	2014-05-22	Scientific Series	View details
Gravity waves from Kerr/CFT	Achilleas Porfyriadis	2014-05-15	Scientific Series	View details
Black holes without Lorentz symmetry	Thomas Sotiriou	2014-05-08	Scientific Series	View details
Geometric inequalities for black holes	Sergio Dain	2014-05-01	Scientific Series	View details
The characteristic structure of the Weyl curvature tensor and its utilization	Fan Zhang	2014-04-24	Scientific Series	View details
Compact objects as dark-matter probes	Paolo Pani	2014-04-17	Scientific Series	View details
Bungee jumping of black holes in AdS universe		2014-03-27	Scientific Series	View details
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

Strong Gravity

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