Quantum Gravity

Displaying 349 - 360 of 486

The imaginary part of the gravitational action and black hole entropy

Yasha Neiman
Okinawa Institute of Science and Technology Graduate University
April 18, 2013

PIRSA:13040106
Quantum Gravity
Quantum causal dynamics without absolute space or time
April 11, 2013

PIRSA:13040083
Quantum Gravity
Canonical gravity using unconstrained null initial data

Michael Reisenberger
Universidad de la Republica Uruguay
March 28, 2013

PIRSA:13030092
Strong Gravity
A CDT Hamiltonian from Horava-Lifshitz gravity

Yuki Sato
Nagoya University
March 14, 2013

PIRSA:13030091
Quantum Gravity
A Self-consistent Model of the Black Hole Evaporation

Yuki Yokokura
RIKEN
March 07, 2013

PIRSA:13030093
Quantum Gravity
The black hole information paradox and its resolution

Ted Jacobson
University of Maryland, College Park
January 17, 2013

PIRSA:13010021
Quantum Gravity
Black holes: To be or not be, that is the question

Luis Garay
Complutense University of Madrid
December 13, 2012

PIRSA:12120032
Quantum Gravity
Renormalizing TGFTs: a 3d example on SU(2)

Sylvain Carrozza
University of Burgundy
December 06, 2012

PIRSA:12120007
Quantum Gravity
Canonical tensor models with local time

Naoki Sasakura
Yukawa Institute for Theoretical Physics
November 15, 2012

PIRSA:12110065
Quantum Gravity
Dynamical evaporation of quantum horizons
November 08, 2012

PIRSA:12110064
Quantum Gravity
Understanding black hole entropy through the renormalization group

Alejandro Satz

October 18, 2012

PIRSA:12100053
Combinatorics and the thermodynamic limit for black holes in Loop Quantum Gravity

Fernando Barbero
Spanish National Research Council (CSIC)
September 13, 2012

PIRSA:12090038
Quantum Gravity

The imaginary part of the gravitational action and black hole entropy

Yasha Neiman
Okinawa Institute of Science and Technology Graduate University
April 18, 2013

PIRSA:13040106
Quantum Gravity
I present a candidate for a new derivation of black hole entropy. The key observation is that the action of General Relativity in bounded regions has an imaginary part, arising from the boundary term. The formula for this imaginary part is closely related to the Bekenstein-Hawking entropy formula, and coincides with it for certain classes of regions. This remains true in the presence of matter, and generalizes appropriately to Lovelock gravity. The imaginary part of the action is a versatile notion, requiring neither stationarity nor any knowledge about asymptotic infinity. Thus, it may provide a handle on quantum gravity in finite and dynamical regions. I derive the above results, make connections with standard approaches to black hole entropy, and speculate on the meaning of it all. Implications for loop quantum gravity are also discussed.
Quantum causal dynamics without absolute space or time
April 11, 2013

PIRSA:13040083
Quantum Gravity
I will describe a discrete model of spacetime which is quantum-mechanical, causal, and background free. The kinematics is described by networks whose vertices are labelled with arrows. These networks can be evolved forwards (or backwards) in time by using unitary replacement rules. The arrow structure permits one to define dynamics without using an absolute time parameter. Based on arXiv:1201.2489.
Canonical gravity using unconstrained null initial data

Michael Reisenberger
Universidad de la Republica Uruguay
March 28, 2013

PIRSA:13030092
Strong Gravity
A CDT Hamiltonian from Horava-Lifshitz gravity

Yuki Sato
Nagoya University
March 14, 2013

PIRSA:13030091
Quantum Gravity
Causal Dynamical Triangulations” (CDT) is a lattice theory where aspects of quantum gravity can be studied. Two-dimensional CDT can be solved analytically and the continuum (quantum) Hamiltonian obtained.
In this talk I will show that this continuum Hamiltonian is the one obtained by quantizing two-dimensional projectable Horava-Lifshitz gravity.
A Self-consistent Model of the Black Hole Evaporation

Yuki Yokokura
RIKEN
March 07, 2013

PIRSA:13030093
Quantum Gravity
We construct a self-consistent model which describes a black hole from formation to evaporation including the back reaction from the Hawking radiation. In the case where a null shell collapses, at the beginning the evaporation occurs, but it stops eventually, and a horizon and singularity appear. On the other hand, in the generic collapse process of a continuously distributed null matter, the black hole evaporates completely without forming a macroscopically large horizon nor singularity. We also find a stationary solution in the heat bath, which can be regarded as a normal thermodynamic object. (hep-th: 1302.4733)
The black hole information paradox and its resolution

Ted Jacobson
University of Maryland, College Park
January 17, 2013

PIRSA:13010021
Quantum Gravity
Both AdS/CFT duality and more general reasoning from quantum gravity point to a rich collection of boundary observables that always evolve unitarily. The physical quantum gravity states described by these observables must be solutions of the spatial diffeomorphism and Wheeler-deWitt constraints, which implies that the state space does not factorize into a tensor product of localized degrees of freedom. The "firewall" argument that unitarity of black hole evaporation is incompatible with a regular near horizon region is based on such a factorization, hence is not applicable in quantum gravity. A version of black hole complementarity resolves the apparent conflict. (I will also discuss doubts and questions.)
Black holes: To be or not be, that is the question

Luis Garay
Complutense University of Madrid
December 13, 2012

PIRSA:12120032
Quantum Gravity
I will review some problems of the black hole paradigm and explore other
possibilities for the final state of stellar collapse other than an evaporating
black hole. In particular I will use the so-called transplanckian problem as a
guide in this search for a compelling scenario for the evaporation of
ultracompact objects.
Renormalizing TGFTs: a 3d example on SU(2)

Sylvain Carrozza
University of Burgundy
December 06, 2012

PIRSA:12120007
Quantum Gravity
I will recall the main motivations for considering spin foam models in their Group Field Theory (GFT) versions, which are quantum field theories defined on group manifolds. As for any other quantum field theory, a fully consistent definition of the latter must involve renormalization. I will briefly review a specific class of GFTs, called tensorial, for which progress in this direction has recently been possible. A new just-renormalizable model, in three dimensions and on the SU(2) group, will be presented. Interestingly, it includes the geometric constraint of the Boulatov model, and might as such be related to Euclidean quantum gravity in three dimensions. Furthermore, this opens the way to a similar analysis of current 4d gravity spin foam models.
Canonical tensor models with local time

Naoki Sasakura
Yukawa Institute for Theoretical Physics
November 15, 2012

PIRSA:12110065
Quantum Gravity
Tensor models are generalization of matrix models, and are studied as discrete models for quantum gravity for more than two-dimensions. Among them, the rank-three tensor models can be interpreted as theories of dynamical fuzzy spaces, and they generally have the feature of
respecting symmetries. In this talk, after briefly reviewing some results on Euclidean models such as spontaneous generation of fuzzy spaces and Euclidean general relativity respecting the diffeomorphism symmetry on them, I will present a way to introduce “local” time to the rank-three tensor models by constructing “local” Hamiltonians. The consistency among the multiple ways of local time evolutions is guaranteed by the on-shell closure of the constraint algebra among the
local Hamiltonians and the symmetry generators of the tensor models. The constraint algebra is shown to approach the DeWitt algebra in a formal continuum limit. I will also discuss the two-fold uniqueness of the local Hamiltonians, and will briefly show some preliminary results on the quantization.
Dynamical evaporation of quantum horizons
November 08, 2012

PIRSA:12110064
Quantum Gravity
We describe of the evaporation process as driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the Loop Quantum Gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of quantum dynamical horizon in terms of a fluctuation-dissipation relation applied to this fundamental discrete structure. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. We show how from this setting the emergence of several conservative scenarios for the final stage of the evaporation process can be microscopically derived. Namely, the leakage of part of the horizon quantum geometry information prior to the Planckian phase and the stabilization of the hole surface shrinkage forming a massive remnant, which can eventually decay, are shown to take place.
Understanding black hole entropy through the renormalization group

Alejandro Satz

October 18, 2012

PIRSA:12100053

It is known that the entanglement entropy of quantum fields on the black hole background contributes to the Bekenstein-Hawking entropy,and that its divergences can be absorbed into the renormalization of gravitational couplings. By introducing a Wilsonian cutoff scale and the concepts of the renormalization group, we can expand this observation into a broader framework for understanding black hole entropy. At a given RG scale, two contributions to the black hole entropy can be identified: the "gravitational" contribution coming from the running effective gravitational action, and the entanglement entropy of the quantum degrees of freedom below the cutoff scale. At different RG scales the balance is different, though the total black hole entropy is invariant. I will describe this picture for free fields, considering both minimal and non-mininal coupling, and discuss the extension to interacting fields and the difficulties it raises.
Combinatorics and the thermodynamic limit for black holes in Loop Quantum Gravity

Fernando Barbero
Spanish National Research Council (CSIC)
September 13, 2012

PIRSA:12090038
Quantum Gravity
The combinatorial problems associated with the counting of black hole states in loop quantum gravity can be analyzed by using suitable generating functions. These not only provide very useful tools for exact computations, but can also be used to perform an statistical analysis of the black hole degeneracy spectrum, study the interesting substructure found in the entropy of microscopic black holes and its asymptotic behavior for large horizon areas. The methods that will be described are relevant for the discussion of the thermodynamic limit for black holes in the area canonical ensemble. This is an important issue in order to understand sub-leading corrections to the Bekenstein-Hawking law.

Title	Speaker(s)	Date	Talk Type	Info
The imaginary part of the gravitational action and black hole entropy	Yasha Neiman	2013-04-18	Scientific Series	View details
Quantum causal dynamics without absolute space or time		2013-04-11	Scientific Series	View details
Canonical gravity using unconstrained null initial data	Michael Reisenberger	2013-03-28	Scientific Series	View details
A CDT Hamiltonian from Horava-Lifshitz gravity	Yuki Sato	2013-03-14	Scientific Series	View details
A Self-consistent Model of the Black Hole Evaporation	Yuki Yokokura	2013-03-07	Scientific Series	View details
The black hole information paradox and its resolution	Ted Jacobson	2013-01-17	Scientific Series	View details
Black holes: To be or not be, that is the question	Luis Garay	2012-12-13	Scientific Series	View details
Renormalizing TGFTs: a 3d example on SU(2)	Sylvain Carrozza	2012-12-06	Scientific Series	View details
Canonical tensor models with local time	Naoki Sasakura	2012-11-15	Scientific Series	View details
Dynamical evaporation of quantum horizons		2012-11-08	Scientific Series	View details
Understanding black hole entropy through the renormalization group	Alejandro Satz	2012-10-18	Scientific Series	View details
Combinatorics and the thermodynamic limit for black holes in Loop Quantum Gravity	Fernando Barbero	2012-09-13	Scientific Series	View details

Quantum Gravity

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