Quantum Gravity

486 talks

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Displaying 313 - 324 of 486

Towards construction of a Wightman QFT in four dimensions

Raimar Wulkenhaar
Westfälische Wilhelms-Universität Münster

August 19, 2014

PIRSA:14080037
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
Quantum Gravity
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
Quantum Gravity
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
Quantum Gravity
From locally covariant QFT to quantum gravity

Katarzyna Rejzner
University of York
May 15, 2014

PIRSA:14050004
Quantum Gravity
Curvature in Noncommutative Geometry

masoud khalkhali
Western University
May 09, 2014

PIRSA:14050064
Mathematical physics
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
Quantum Gravity
Group Field Theory in dimension 4 - ε

Sylvain Carrozza
University of Burgundy
May 01, 2014

PIRSA:14050001
Quantum Gravity
Universal problems

David Mattingly
University of New Hampshire
April 17, 2014

PIRSA:14040074
Quantum Gravity
Quantum cosmology in Lorentz-violating gravity
April 10, 2014

PIRSA:14040079
Quantum Gravity
Quantum Gravity, Trees, and Polynomials

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

PIRSA:14040134
Quantum Gravity
Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes

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

PIRSA:14030115
Quantum Gravity

Towards construction of a Wightman QFT in four dimensions

Raimar Wulkenhaar
Westfälische Wilhelms-Universität Münster

August 19, 2014

PIRSA:14080037

We prove that the $\lambda\phi^4_4$ quantum field theory on noncommutative Moyal space is, in the limit of infinite noncommutativity, exactly solvable in terms of the solution of a non-linear integral equation. The proof involves matrix model techniques which might be relevant for 2D quantum gravity and its generalisation to coloured tensor models of rank $\geq 3$. Surprisingly, our limit describes Schwinger functions of a Euclidean quantum field theory on standard $\mathbb{R}^4$ which satisfy the easy Osterwalder-Schrader axioms boundedness, covariance and symmetry. We prove that the decisive reflection positivity axiom is, for the 2-point function, equivalent to the question whether or not the solution of the integral equation is a Stieltjes function. The numerical solution of the integral equation leaves no doubt that this is true for coupling constants $\lambda\in[-0.39,0]$.
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
Quantum Gravity
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
Quantum Gravity
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.
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
Quantum Gravity
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.
From locally covariant QFT to quantum gravity

Katarzyna Rejzner
University of York
May 15, 2014

PIRSA:14050004
Quantum Gravity
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).
Curvature in Noncommutative Geometry

masoud khalkhali
Western University
May 09, 2014

PIRSA:14050064
Mathematical physics
After the seminal work of Connes and Tretkoff on the Gauss-Bonnet theorem for the noncommutative 2-torus and its extension by Fathizadeh and myself, there have been significant developments in understanding the local differential geometry of these noncommutative spaces equipped with curved metrics. In this talk, I will review a series of joint works with Farzad Fathizadeh in which we compute the scalar curvature for curved noncommutative tori and prove the analogue of Weyl's law and Connes' trace theorem. Our final formula for the curvature matches precisely with the one computed independently by A. Connes and H. Moscovici. I will then report on our recent work on the computation of scalar curvature for noncommutative 4-tori (which involves intricacies due to violation of the Kähler condition). We show that metrics with constant curvature are extrema of the analogue of the Einstein–Hilbert action. A purely noncommutative feature in these works is the appearance of the modular automorphism from Tomita–Takesaki theory of KMS states in the final formulas for the curvature.
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
Quantum Gravity
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
Quantum Gravity
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
Quantum Gravity
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
Quantum Gravity
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
Quantum Gravity
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
Quantum Gravity
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.

Title	Speaker(s)	Date	Talk Type	Info
Towards construction of a Wightman QFT in four dimensions	Raimar Wulkenhaar	2014-08-19	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
Last gasp ‎of a black hole: why unitary evaporation must be non-monotonic	Matteo Smerlak	2014-05-29	Scientific Series	View details
From locally covariant QFT to quantum gravity	Katarzyna Rejzner	2014-05-15	Scientific Series	View details
Curvature in Noncommutative Geometry	masoud khalkhali	2014-05-09	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
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

Quantum Gravity

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