Quantum Gravity

492 talks

S005

Collection TypeSeries

Source RepositoryPIRSA

Displaying 325 - 336 of 492

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
Group Field Theory in dimension 4 - ε

Sylvain Carrozza University of Burgundy
May 01, 2014

PIRSA:14050001
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
Quantum Gravity, Trees, and Polynomials

Fabien Vignes-Tourneret Université Claude Bernard Lyon 1
April 03, 2014

PIRSA:14040134
General Relativity & Quantum Cosmology
Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)
March 27, 2014

PIRSA:14030115
General Relativity & Quantum Cosmology
A one-dimensional action for simplicial gravity in three dimensions

Wolfgang Wieland University of Erlangen-Nuremberg
March 06, 2014

PIRSA:14030088
General Relativity & Quantum Cosmology
Nonlocal cosmology

Richard Woodard University of Florida
February 27, 2014

PIRSA:14020137
General Relativity & Quantum Cosmology
Quantum Raychaudhuri equation

Saurya Das University of Lethbridge
February 20, 2014

PIRSA:14020130
General Relativity & Quantum Cosmology
Firewall evasion by quantum gravity

Ted Jacobson University of Maryland, College Park
February 13, 2014

PIRSA:14020136
General Relativity & Quantum Cosmology
Black hole entropy and the case for self-dual loop quantum gravity
January 29, 2014

PIRSA:14010098
General Relativity & Quantum Cosmology
Wilson Lines in Higher Spin Gravity

Alejandra Castro University of Cambridge
January 23, 2014

PIRSA:14010081
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
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.
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.
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.
Quantum Gravity, Trees, and Polynomials

Fabien Vignes-Tourneret Université Claude Bernard Lyon 1
April 03, 2014

PIRSA:14040134
General Relativity & Quantum Cosmology
The perturbative series of colored group field theory are governed by a combinatorial 1/N-expansion. Controlling its coefficients is essential in order to understand the continuum limit. I will show how such a program is naturally related to higher-dimensional generalizations of trees in a colored Boulatov-Ooguri model, and present some partial results on the enumeration of such strucures in melonic graphs. This talk is mainly based on recent results by Baratin, Carrozza, Oriti, Ryan, and Smerlak ("Melonic phase transition in group field theory". arXiv: 1307.5026).
Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)
March 27, 2014

PIRSA:14030115
General Relativity & Quantum Cosmology
Recent implications of results from quantum information theory applied to black holes has led to the confusing conclusions that requires either abandoning the equivalence principle (e.g. the firewall picture), or the no-hair theorem (e.g. the fuzzball picture), or even more unpalatable options. The recent discovery of a pulsar orbiting a black hole opens up new possibilities for tests of theories of gravity. We examine possible observational effects of semiclassical quantum gravity in the vicinity of black holes, as probed by pulsars and event horizon telescope imaging of flares. Pulsar radiation is observable at wavelengths only two orders of magnitude shorter than the Hawking radiation, so precision interferometry of lensed pulsar images may shed light on the quantum gravitational processes and interaction of Hawking radiation with the spacetime near the black hole. This paper discusses the impact on the pulsar radiation interference pattern, which is observable through the modulation index in the foreseeable future, and discusses a possible classical limit of BHC.
A one-dimensional action for simplicial gravity in three dimensions

Wolfgang Wieland University of Erlangen-Nuremberg
March 06, 2014

PIRSA:14030088
General Relativity & Quantum Cosmology
Loop quantum gravity has a spinorial representation. Spinors simplify the symplectic structure of the theory, but can they also teach us something about the dynamics? We study this question in three dimensions, and derive the Ponzano–-Regge model from a spinorial action. Our construction starts from the first-order Palatini formalism, and gives the discretised action in the spinorial representation. A one-dimensional refinement limit brings us back to a continuum theory. The three-dimensional action turns into a line integral over the edges of the discretisation. We compute the gauge-fixed path integral for a generic simplicial discretisation. The resulting amplitudes reproduce the Ponzano–-Regge model.
Nonlocal cosmology

Richard Woodard University of Florida
February 27, 2014

PIRSA:14020137
General Relativity & Quantum Cosmology
I review a class of nonlocally modified gravity models which were proposed to explain the current phase of cosmic acceleration without dark energy. Among the topics considered are deriving causal and conserved field equations, adjusting the model to make it support a given expansion history, why these models do not require an elaborate screening mechanism to evade solar system tests, degrees of freedom and kinetic stability, and the negative verdict of structure formation. Although these simple models are not consistent with data on the growth of cosmic structures many of their features are likely to carry over to more complicated models which are in better agreement with the data.
Quantum Raychaudhuri equation

Saurya Das University of Lethbridge
February 20, 2014

PIRSA:14020130
General Relativity & Quantum Cosmology
We compute quantum corrections to the Raychaudhuri equation, by replacing classical geodesics with quantal (Bohmian) trajectories, and show that they prevent focusing of geodesics, and the formation of conjugate points. We discuss implications for the Hawking-Penrose singularity theorems, and for curvature singularities. Reference: arXiv: 1311.6539
Firewall evasion by quantum gravity

Ted Jacobson University of Maryland, College Park
February 13, 2014

PIRSA:14020136
General Relativity & Quantum Cosmology
It has been argued that if black hole evaporation is a unitary quantum process, then a black hole horizon must be cloaked by a "firewall", i.e. a highly excited state of local quantum fields. This reasoning is based on factorizing the Hilbert space into interior and exterior degrees of freedom. Such factorization ignores the Wheeler-deWitt constraint equation, which arises from the diffeomorphism invariance of quantum gravity. I will argue that this constraint evades the firewall.
Black hole entropy and the case for self-dual loop quantum gravity
January 29, 2014

PIRSA:14010098
General Relativity & Quantum Cosmology
By focusing on aspects of black hole thermodynamics, I will present some evidences supporting the unexpected role of the complex self-dual variables in quantum gravity. This will also be the occasion of revisiting some aspects of three-dimensional gravity, and in particular the link between the BTZ black hole and the Turaev-Viro state sum model. Also the information on the website for next week needs to be modified: We will not have a seminar on Thursday (as Thursday is PI day). Instead, we will have the seminar on Wednesday, but actually would prefer a different time, namely 3.30 pm.
Wilson Lines in Higher Spin Gravity

Alejandra Castro University of Cambridge
January 23, 2014

PIRSA:14010081
General Relativity & Quantum Cosmology
In this talk I will review the interpretation of Wilson line operators in the context of higher spin gravity in 2+1 dim and holography. I will show how a Wilson line encapsulates the thermodynamics of black holes. Furthermore it provides an elegant description of massive particles. This opens a new window of observables which will allow us to probe the true geometrical nature of higher spin gravity.

Title	Speaker(s)	Date	Talk Type	Info
On the role of the extra kinetic term coupling ƛ in classical Hořava-Lifshitz gravity	Luis Pires	2014-05-08	Scientific Series	View details
Group Field Theory in dimension 4 - ε	Sylvain Carrozza	2014-05-01	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
Quantum Gravity, Trees, and Polynomials	Fabien Vignes-Tourneret	2014-04-03	Scientific Series	View details
Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes	Ue-Li Pen	2014-03-27	Scientific Series	View details
A one-dimensional action for simplicial gravity in three dimensions	Wolfgang Wieland	2014-03-06	Scientific Series	View details
Nonlocal cosmology	Richard Woodard	2014-02-27	Scientific Series	View details
Quantum Raychaudhuri equation	Saurya Das	2014-02-20	Scientific Series	View details
Firewall evasion by quantum gravity	Ted Jacobson	2014-02-13	Scientific Series	View details
Black hole entropy and the case for self-dual loop quantum gravity		2014-01-29	Scientific Series	View details
Wilson Lines in Higher Spin Gravity	Alejandra Castro	2014-01-23	Scientific Series	View details

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Format results

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

Group Field Theory in dimension 4 - ε

Universal problems

Quantum cosmology in Lorentz-violating gravity

Quantum Gravity, Trees, and Polynomials

Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes

A one-dimensional action for simplicial gravity in three dimensions

Nonlocal cosmology

Quantum Raychaudhuri equation

Firewall evasion by quantum gravity

Black hole entropy and the case for self-dual loop quantum gravity

Wilson Lines in Higher Spin Gravity

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

Group Field Theory in dimension 4 - ε

Universal problems

Quantum cosmology in Lorentz-violating gravity

Quantum Gravity, Trees, and Polynomials

Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes

A one-dimensional action for simplicial gravity in three dimensions

Nonlocal cosmology

Quantum Raychaudhuri equation

Firewall evasion by quantum gravity

Black hole entropy and the case for self-dual loop quantum gravity

Wilson Lines in Higher Spin Gravity