General Relativity & Quantum Cosmology

Displaying 1345 - 1356 of 1843

A mechanism for vortex annihilation in two dimensional superfluid turbulence

Andrew Lucas University of Colorado Boulder
May 22, 2014

PIRSA:14050139
General Relativity & Quantum Cosmology
From locally covariant QFT to quantum gravity

Katarzyna Rejzner University of York
May 15, 2014

PIRSA:14050004
General Relativity & Quantum Cosmology
Gravity waves from Kerr/CFT

Achilleas Porfyriadis Harvard University
May 15, 2014

PIRSA:14050009
General Relativity & Quantum Cosmology
On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity

Luis Pires Radboud Universiteit Nijmegen
May 08, 2014

PIRSA:14050061
General Relativity & Quantum Cosmology
Black holes without Lorentz symmetry

Thomas Sotiriou University of Nottingham
May 08, 2014

PIRSA:14050002
General Relativity & Quantum Cosmology
Group Field Theory in dimension 4 - ε

Sylvain Carrozza University of Burgundy
May 01, 2014

PIRSA:14050001
General Relativity & Quantum Cosmology
Geometric inequalities for black holes

Sergio Dain Universidad Nacional de Cordoba
May 01, 2014

PIRSA:14050030
General Relativity & Quantum Cosmology
The characteristic structure of the Weyl curvature tensor and its utilization

Fan Zhang Beijing Normal University
April 24, 2014

PIRSA:14040139
General Relativity & Quantum Cosmology
Compact objects as dark-matter probes

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

PIRSA:14040078
General Relativity & Quantum Cosmology
Universal problems

David Mattingly University of New Hampshire
April 17, 2014

PIRSA:14040074
General Relativity & Quantum Cosmology
Quantum cosmology in Lorentz-violating gravity
April 10, 2014

PIRSA:14040079
General Relativity & Quantum Cosmology
A non-commuting stabilizer formalism

Xiaotong Ni Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
April 09, 2014

PIRSA:14040136
Quantum Physics

General Relativity & Quantum Cosmology

A mechanism for vortex annihilation in two dimensional superfluid turbulence

Andrew Lucas University of Colorado Boulder
May 22, 2014

PIRSA:14050139
General Relativity & Quantum Cosmology
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.
From locally covariant QFT to quantum gravity

Katarzyna Rejzner University of York
May 15, 2014

PIRSA:14050004
General Relativity & Quantum Cosmology
Locally covariant quantum field theory (LCQFT) has proven to be a very successful framework for QFT on curved spacetimes. It is natural to ask, how far these ideas can be generalized and if one can learn something about quantum gravity, using LCQFT methods. In particular, one can use the relative Cauchy evolution to formulate the notion of background independence. Recently we have proven that background independence in this sense holds for effective quantum gravity, formulated as a perturbative QFT. Remarkably, the formalism of LCQFT can be extended to structures more general than spacetimes. The essential feature is the presence of the causal structure. An example application would be QFT on causal sets (work in progress).
Gravity waves from Kerr/CFT

Achilleas Porfyriadis Harvard University
May 15, 2014

PIRSA:14050009
General Relativity & Quantum Cosmology
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.
On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity

Luis Pires Radboud Universiteit Nijmegen
May 08, 2014

PIRSA:14050061
General Relativity & Quantum Cosmology
We study the classical constraint algebra of Hořava-Lifshitz gravity, where due to the breaking of 4d diffeomorphism symmetry, there is a new dimensionless coupling absent in GR and whose role is not yet clear. Starting from two apparently contradictory results, we show how the role of the extra coupling differs between the projectable and non-projectable versions of the theory. In particular, we see how in the latter, it gives rise to a non-trivial constraint algebra, akin to the conditions seen in the CMC gauge of GR.
Black holes without Lorentz symmetry

Thomas Sotiriou University of Nottingham
May 08, 2014

PIRSA:14050002
General Relativity & Quantum Cosmology
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.
Group Field Theory in dimension 4 - ε

Sylvain Carrozza University of Burgundy
May 01, 2014

PIRSA:14050001
General Relativity & Quantum Cosmology
Rank 3 tensorial group fields theories with gauge invariance condition appear to be renormalizable on dimension 3 groups such as SU(2), but also on dimension 4 groups. Building on an analogy with ordinary scalar field theories, I will generalize such models to group dimension 4 - ε, and discuss what this might teach us about the physically relevant SU(2) case.
Geometric inequalities for black holes

Sergio Dain Universidad Nacional de Cordoba
May 01, 2014

PIRSA:14050030
General Relativity & Quantum Cosmology
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
General Relativity & Quantum Cosmology
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
General Relativity & Quantum Cosmology
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.
Universal problems

David Mattingly University of New Hampshire
April 17, 2014

PIRSA:14040074
General Relativity & Quantum Cosmology
Arguments that gravity cannot be a local renormalizable quantum field theory come from both field theory lore and black hole physics. Two current approaches to quantum gravity, asymptotic safety and Horava-Lifshitz gravity, both of which treat quantum gravity as a local renormalizable QFT, are explicitly constructed to counter field theory arguments about the non-renormalizability of gravity. However, any proposed renormalizable theory of quantum gravity must also answer black hole physics based counter-arguments. Formulating these arguments concretely requires understanding black hole solutions and thermodynamics in these theories. For Horava-Lifshitz gravity this entails understanding the thermodynamics of universal horizons. I describe the current status of universal horizon physics and which aspects are/are not still in tension with the fundamental premise of renormalizability.
Quantum cosmology in Lorentz-violating gravity
April 10, 2014

PIRSA:14040079
General Relativity & Quantum Cosmology
Lorentz invariance is considered a fundamental symmetry of physical theories. However, while Lorentz violations are strongly constrained in the matter sector, constraints in the gravitational sector are weaker, allowing to contemplate the idea of Lorentz-violating gravity theories. In this talk I will discuss the effects of Lorentz violations in the quantum cosmology scenario by analyzing the properties of a simple anisotropic model in the framework of Horava-Lifshitz gravity and, if time permitting, some partial results on the viability of this class of theories.
A non-commuting stabilizer formalism

Xiaotong Ni Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
April 09, 2014

PIRSA:14040136
Quantum Physics

General Relativity & Quantum Cosmology
We propose a non-commutative extension of the Pauli stabilizer formalism. The aim is to describe a class of many-body quantum states which is richer than the standard Pauli stabilizer states. In our framework, stabilizer operators are tensor products of single-qubit operators drawn from the group {\alpha I, X,S}, where \alpha=e^{i\pi/4} and S=diag(1,i). We provide techniques to efficiently compute various properties, related to e.g. bipartite entanglement, expectation values of local observables, preparation by means of quantum circuits, parent Hamiltonians etc. We also highlight significant differences compared to the Pauli stabilizer formalism. In particular we give examples of states in our formalism which cannot arise in the Pauli stabilizer formalism, such as topological models that supports non-abelian anyons. This is a joint work with O. Buerschaper and M. van den Nest.

Title	Speaker(s)	Date	Talk Type	Info link
A mechanism for vortex annihilation in two dimensional superfluid turbulence	Andrew Lucas	2014-05-22	Scientific Series	View details
From locally covariant QFT to quantum gravity	Katarzyna Rejzner	2014-05-15	Scientific Series	View details
Gravity waves from Kerr/CFT	Achilleas Porfyriadis	2014-05-15	Scientific Series	View details
On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity	Luis Pires	2014-05-08	Scientific Series	View details
Black holes without Lorentz symmetry	Thomas Sotiriou	2014-05-08	Scientific Series	View details
Group Field Theory in dimension 4 - ε	Sylvain Carrozza	2014-05-01	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
Universal problems	David Mattingly	2014-04-17	Scientific Series	View details
Quantum cosmology in Lorentz-violating gravity		2014-04-10	Scientific Series	View details
A non-commuting stabilizer formalism	Xiaotong Ni	2014-04-09	Scientific Series	View details

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General Relativity & Quantum Cosmology

Format results

A mechanism for vortex annihilation in two dimensional superfluid turbulence

From locally covariant QFT to quantum gravity

Gravity waves from Kerr/CFT

On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity

Black holes without Lorentz symmetry

Group Field Theory in dimension 4 - ε

Geometric inequalities for black holes

The characteristic structure of the Weyl curvature tensor and its utilization

Compact objects as dark-matter probes

Universal problems

Quantum cosmology in Lorentz-violating gravity

A non-commuting stabilizer formalism

A mechanism for vortex annihilation in two dimensional superfluid turbulence

From locally covariant QFT to quantum gravity

Gravity waves from Kerr/CFT

On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity

Black holes without Lorentz symmetry

Group Field Theory in dimension 4 - ε

Geometric inequalities for black holes

The characteristic structure of the Weyl curvature tensor and its utilization

Compact objects as dark-matter probes

Universal problems

Quantum cosmology in Lorentz-violating gravity

A non-commuting stabilizer formalism