General Relativity & Quantum Cosmology

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Probing (beyond) general relativity with compact binaries and gravitational waves

Leo Stein Cornell University
October 02, 2014

PIRSA:14100003
General Relativity & Quantum Cosmology
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
High Energy Physics

Condensed Matter

General Relativity & Quantum Cosmology
Observables and Change in Totally Constrained Systems

Karim Thebault Ludwig-Maximilians-Universität München (LMU)
September 18, 2014

PIRSA:14090004
General Relativity & Quantum Cosmology
Force-Free Electrodynamics around Extreme Kerr Black Holes

Maria J. Rodriguez Utah State University
September 11, 2014

PIRSA:14090065
General Relativity & Quantum Cosmology
Firewalls- A GR perspective

Bill Unruh University of British Columbia
September 04, 2014

PIRSA:14090066
General Relativity & Quantum Cosmology
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Eyo Ita US Naval Academy and Cambridge University (DAMTP)
July 31, 2014

PIRSA:14070033
General Relativity & Quantum Cosmology
Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...

Stefano Liberati SISSA International School for Advanced Studies
June 19, 2014

PIRSA:14060002
General Relativity & Quantum Cosmology
Analogue Models of Gravity: The ubiquitous space-time

Stefano Liberati SISSA International School for Advanced Studies
June 18, 2014

PIRSA:14060000
General Relativity & Quantum Cosmology
Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic

Matteo Smerlak Capital Fund Management S.A.
May 29, 2014

PIRSA:14050027
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
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

Probing (beyond) general relativity with compact binaries and gravitational waves

Leo Stein Cornell University
October 02, 2014

PIRSA:14100003
General Relativity & Quantum Cosmology
General relativity enjoys phenomenal success in agreeing with experiments and observations, but it must break down at some point. Astrophysics can give guidance for what type of theory may correct general relativity, if we know which phenomenology to look for. I will discuss the possible corrections to the structure of compact objects, the binary problem, and observations with pulsar timing and gravitational wave detection. These corrections are computed in specific effective theories, such as Einstein-dilaton-Gauss-Bonnet (EdGB) and dynamical Chern-Simons (dCS) gravity, and we may further generalize the common aspects of these theories to build a parametrized framework which captures a large number of effective field theories.
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
High Energy Physics

Condensed Matter

General Relativity & Quantum Cosmology
We discuss properties of 2-point functions in CFTs in 2+1D at finite temperature. For concreteness, we focus on those involving conserved flavour currents, in particular on the associated conductivity. At frequencies much greater than the temperature, ω >> T, the ω dependence of the conductivity can be computed from the operator product expansion (OPE) between the currents and operators which acquire a non-zero expectation value at T > 0. Such results are found to be in excellent agreement with quantum Monte Carlo studies of the O(2) Wilson-Fisher CFT. Results for the conductivity and other observables are also obtained in vector 1/N expansions. We match these large ω results to the corresponding correlators of holographic representations of the CFT: the holographic approach then allows us to extrapolate to small ω/T. Other holographic studies implicitly only used the OPE between the currents and the energy-momentum tensor, and this yields the correct leading large ω behavior for a large class of CFTs. However, for the Wilson-Fisher CFT a relevant “thermal” operator must also be considered, and then consistency with the Monte Carlo results is obtained without a previously needed ad hoc rescaling of the T value [1]. We also use the OPE to prove sum rules obeyed by the conductivity. **In collaboration with A. Katz, S. Sachdev and E. Sørensen** [1] WWK, E. Sørensen, S. Sachdev, Nat. Phys. 10, 361 (2014)
Observables and Change in Totally Constrained Systems

Karim Thebault Ludwig-Maximilians-Universität München (LMU)
September 18, 2014

PIRSA:14090004
General Relativity & Quantum Cosmology
We isolate an important physical distinction between gauge symmetries which exist at the level of histories and states, and those which exist at the level of histories and not states. This distinction is characterised explicitly using a generalized Hamilton-Jacobi formalism within which a non-standard prescription for the observables of classical totally constrained systems is developed. These ideas motivate a `relational quantization' procedure which is different from the standard `Dirac quanization'. In particular, relational quantization of totally constrained systems leads to a formalism with superpositions of energy eigenstates and an enlarged set of quantum observables. These `Kucha\v{r} observables' can change independently of each other, and thus are associated with measurable quantities in excess of the `perennials' of the standard Dirac approach.
Force-Free Electrodynamics around Extreme Kerr Black Holes

Maria J. Rodriguez Utah State University
September 11, 2014

PIRSA:14090065
General Relativity & Quantum Cosmology
Plasma-filled magnetospheres can extract energy from a spinning black hole and provide the power source for a variety of observed astrophysical phenomena. These magnetospheres are described by the highly nonlinear equations of force-free electrodynamics, or FFE. Typically these equations can only be solved numerically. In this talk I will explain how to analytically obtain several infinite families of exact solutions of the full nonlinear FFE equations very near the horizon of a maximally spinning black hole, where the energy extraction takes place.
Firewalls- A GR perspective

Bill Unruh University of British Columbia
September 04, 2014

PIRSA:14090066
General Relativity & Quantum Cosmology
This talk will examine the Firewall argument and a number of possible approaches to it, with a variety of simple examples to try to clarify various aspects of the arguments.
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Eyo Ita US Naval Academy and Cambridge University (DAMTP)
July 31, 2014

PIRSA:14070033
General Relativity & Quantum Cosmology
The authors have revealed a fundamental structure which has been hidden within the Wheeler-DeWitt (WDW) constraint of four dimensional General Relativity (GR) of Lorentzian signature in the Ashtekar self-dual variables. The WDW equation can be written as the commutator of two geometric entities, namely the imaginary part of the Chern-Simons functional Q and the local volume element V(x) of 3-space. Upon quantization with cosmological constant, the WDW equation takes on the form of the Lie algebra of the affine group of transformations of the straight line, with Q and V(x) playing the role of the generators for the Lie algebra. The generators are Hermitian, which addresses the issue of the implementation of the reality conditions of GR at the quantum level. Additionally, the irreducible unitary representations (IUR) implement the positivity of the spectrum of the volume operator V(x) at the quantum level This development has led to the existence of elements of the physical Hilbert space for four dimensional gravity of Lorentzian signature, the full theory, in the form of irreducible, unitary representations of the affine group of transformations of the straight line. The affine Lie algebraic structure of the WDW equation remains intact even in the presence of nongravitational fields. This feature has led to the extension of the affine group formulation to elements of the physical Hilbert space for gravity coupled to the full Standard Model of particle physics, quantized on equal footing. Work on the physical interpretation of the states with respect to gauge-diffeomorphism invariant observables, and spacetime geometries solving the Einstein equations is in progress. The journal reference for these results are as follows: - The first result has been published in CQG 30 (2013) 065013 - The second result has just been published in Annals of Physics Journal Vol.343, pages 153-163, April 2014
Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...

Stefano Liberati SISSA International School for Advanced Studies
June 19, 2014

PIRSA:14060002
General Relativity & Quantum Cosmology
Thermodynamical aspects of gravity have been a tantalising puzzle for more than forty years now and are still at the center of much activity in semiclassical and quantum gravity. We shall explore the possibility that they might hint toward an emergent nature of gravity exploring the possible implications of such hypothesis. Among these we shall focus on the possibility that Lorentz invariance might be only a low energy/emergent feature by discussing viable theoretical frameworks, present constraints and open issues which make this path problematic. In the end we shall focus on black hole thermodynamics in Lorentz breaking gravity by presenting some recent results that seems to hint towards a surprising resilience of thermodynamics aspect of gravity even in these scenarios.
Analogue Models of Gravity: The ubiquitous space-time

Stefano Liberati SISSA International School for Advanced Studies
June 18, 2014

PIRSA:14060000
General Relativity & Quantum Cosmology
Analogies have played a very important role in physics and mathematics, as they provide new ways of looking at problems that permit cross-fertilization of ideas among different branches of science. An analogue gravity model is a generic dynamical system (typically but not always based on condensed matter physics) where the propagation of excitations/perturbations can be described via hyperbolic equations of motion possibly characterized be one single metric element for all the perturbations. We shall review the historical development of this field, some of the systems proposed, and discuss several applications of this fruitful analogy mainly in the context of black hole physics and cosmology. While typical applications are in the realm of classical and quantum field theory on curved spacetime, I shall in the end also discuss recent developments which may provide insights about the possible nature of gravitational dynamics in emergent gravity scenarios.
Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic

Matteo Smerlak Capital Fund Management S.A.
May 29, 2014

PIRSA:14050027
General Relativity & Quantum Cosmology
I will describe the relationship between radiated energy and entanglement entropy of massless fields at future null infinity (the "Page curve") in two-dimensional models of black hole evaporation. ‎I will use this connection to derive a general feature of any unitary-preserving evaporation scenario: the Bondi mass of the hole must be non-monotonic. Time permitting, I will comment on time scales in such scenarios.
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.

Title	Speaker(s)	Date	Talk Type	Info link
Probing (beyond) general relativity with compact binaries and gravitational waves	Leo Stein	2014-10-02	Scientific Series	View details
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography		2014-09-19	Scientific Series	View details
Observables and Change in Totally Constrained Systems	Karim Thebault	2014-09-18	Scientific Series	View details
Force-Free Electrodynamics around Extreme Kerr Black Holes	Maria J. Rodriguez	2014-09-11	Scientific Series	View details
Firewalls- A GR perspective	Bill Unruh	2014-09-04	Scientific Series	View details
Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.	Eyo Ita	2014-07-31	Scientific Series	View details
Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...	Stefano Liberati	2014-06-19	Scientific Series	View details
Analogue Models of Gravity: The ubiquitous space-time	Stefano Liberati	2014-06-18	Scientific Series	View details
Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic	Matteo Smerlak	2014-05-29	Scientific Series	View details
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

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General Relativity & Quantum Cosmology

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Probing (beyond) general relativity with compact binaries and gravitational waves

Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography

Observables and Change in Totally Constrained Systems

Force-Free Electrodynamics around Extreme Kerr Black Holes

Firewalls- A GR perspective

Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...

Analogue Models of Gravity: The ubiquitous space-time

Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic

A mechanism for vortex annihilation in two dimensional superfluid turbulence

From locally covariant QFT to quantum gravity

Gravity waves from Kerr/CFT

Probing (beyond) general relativity with compact binaries and gravitational waves

Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography

Observables and Change in Totally Constrained Systems

Force-Free Electrodynamics around Extreme Kerr Black Holes

Firewalls- A GR perspective

Physical Hilbert space for the affine group formulation of 4D, gravity of Lorentzian signature.

Gravity, an unexpected journey: from thermodynamics to emergent gravity, Lorentz breaking and back...

Analogue Models of Gravity: The ubiquitous space-time

Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic

A mechanism for vortex annihilation in two dimensional superfluid turbulence

From locally covariant QFT to quantum gravity

Gravity waves from Kerr/CFT