General Relativity & Quantum Cosmology

Displaying 1333 - 1344 of 1843

Complex Loop Quantum Cosmology

Jibril BEN ACHOUR Arnold Sommerfeld Center (Germany) / ENS de Lyon (France)
October 30, 2014

PIRSA:14100047
General Relativity & Quantum Cosmology
Is B-Mode Polarization of the CMB the Holy Grail of Inflation?

Robert Brandenberger McGill University - Department of Physics
October 16, 2014

PIRSA:14100002
General Relativity & Quantum Cosmology
Spinning Black Holes and the Membrane Paradigm

Robert Penna Massachusetts Institute of Technology (MIT)
October 16, 2014

PIRSA:14100007
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
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-Universitiät München (LMU)
September 18, 2014

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

Maria 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

Complex Loop Quantum Cosmology

Jibril BEN ACHOUR Arnold Sommerfeld Center (Germany) / ENS de Lyon (France)
October 30, 2014

PIRSA:14100047
General Relativity & Quantum Cosmology
We study in the context of loop quantum cosmology the effect of the analytic continuation that sends the Barbero-Immirzi parameter to a purely imaginary value. We show that this construction leads once again to a bouncing scenario, in which however the contracting and expanding phases on each side of the bounce are not symmetrical. Moreover, the minimal volume reached by the universe and the critical matter density become naturally independent of the Barbero-Immirzi parameter. This analytic continuation was first proposed in the context of black hole entropy calculation, and constitutes a proposal for defining a theory of self-dual quantum gravity in terms of the complex Ashtekar connection and for solving the so-called reality conditions. We expect that the systematic investigation of this analytic continuation in various setups will eventually lead to new insights on the status of the quantum states of complex Ashtekar gravity.
Is B-Mode Polarization of the CMB the Holy Grail of Inflation?

Robert Brandenberger McGill University - Department of Physics
October 16, 2014

PIRSA:14100002
General Relativity & Quantum Cosmology
I will discuss why the search for B-Mode Polarization of the Cosmic Microwave Background (CMB) is very important for early universe cosmology, but that a discovery of such a polarization mode is in no way a confirmation of inflationary cosmology.
Spinning Black Holes and the Membrane Paradigm

Robert Penna Massachusetts Institute of Technology (MIT)
October 16, 2014

PIRSA:14100007
General Relativity & Quantum Cosmology
There are about nine astrophysical black holes with measurements of the black hole's spin via the continuum fitting method. Several of these black holes drive powerful jets, which appear to extract the black hole's rotational energy. I will discuss the theory behind these observations, with a particular focus on the black hole membrane paradigm. The membrane paradigm is useful on a practical level for understanding black hole jets. However, it may also be related to fundamental physics through holography and AdS/CFT. This suggests new opportunities for interactions between fundamental physics and astrophysics.
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-Universitiät 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 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.

Title	Speaker(s)	Date	Talk Type	Info link
Complex Loop Quantum Cosmology	Jibril BEN ACHOUR	2014-10-30	Scientific Series	View details
Is B-Mode Polarization of the CMB the Holy Grail of Inflation?	Robert Brandenberger	2014-10-16		View details
Spinning Black Holes and the Membrane Paradigm	Robert Penna	2014-10-16	Scientific Series	View details
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 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

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General Relativity & Quantum Cosmology

Format results

Complex Loop Quantum Cosmology

Is B-Mode Polarization of the CMB the Holy Grail of Inflation?

Spinning Black Holes and the Membrane Paradigm

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

Complex Loop Quantum Cosmology

Is B-Mode Polarization of the CMB the Holy Grail of Inflation?

Spinning Black Holes and the Membrane Paradigm

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