Quantum Gravity

503 talks

S005

Collection TypeSeries

Source RepositoryPIRSA

Displaying 325 - 336 of 503

Worldline formalism for covariant loop gravity

Wolfgang Wieland University of Erlangen-Nuremberg
November 06, 2014

PIRSA:14110116
General Relativity & Quantum Cosmology
Complex Loop Quantum Cosmology

Jibril Ben Achour Ludwig-Maximilians-Universität München (LMU)
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
Observables and Change in Totally Constrained Systems

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

PIRSA:14090004
General Relativity & Quantum Cosmology
Firewalls- A GR perspective

Bill Unruh University of British Columbia
September 04, 2014

PIRSA:14090066
General Relativity & Quantum Cosmology
Towards construction of a Wightman QFT in four dimensions

Raimar Wulkenhaar University of 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
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
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
From locally covariant QFT to quantum gravity

Katarzyna Rejzner University of York
May 15, 2014

PIRSA:14050004
General Relativity & Quantum Cosmology
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
General Relativity & Quantum Cosmology

Worldline formalism for covariant loop gravity

Wolfgang Wieland University of Erlangen-Nuremberg
November 06, 2014

PIRSA:14110116
General Relativity & Quantum Cosmology
I present a proposal for a worldline action for discretized gravity with the same field content as loop quantum gravity. The proposal is defined through its action, which is a one-dimensional integral over the edges of the discretization. Every edge carries a finite-dimensional phase space, and the evolution equations are generated by a Hamiltonian, which is a sum over the constraints of the theory. I will explain the relevance of the model, and close with possible relations to other approaches of quantum gravity, including: relative locality, causal sets and twistor theory.
Complex Loop Quantum Cosmology

Jibril Ben Achour Ludwig-Maximilians-Universität München (LMU)
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.
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.
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.
Towards construction of a Wightman QFT in four dimensions

Raimar Wulkenhaar University of 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
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.
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.
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).
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
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.

Title	Speaker(s)	Date	Talk Type	Info
Worldline formalism for covariant loop gravity	Wolfgang Wieland	2014-11-06	Scientific Series	View details
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
Observables and Change in Totally Constrained Systems	Karim Thebault	2014-09-18	Scientific Series	View details
Firewalls- A GR perspective	Bill Unruh	2014-09-04	Scientific Series	View details
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

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Format results

Worldline formalism for covariant loop gravity

Complex Loop Quantum Cosmology

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

Observables and Change in Totally Constrained Systems

Firewalls- A GR perspective

Towards construction of a Wightman QFT in four dimensions

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...

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

From locally covariant QFT to quantum gravity

Curvature in Noncommutative Geometry

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

Worldline formalism for covariant loop gravity

Complex Loop Quantum Cosmology

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

Observables and Change in Totally Constrained Systems

Firewalls- A GR perspective

Towards construction of a Wightman QFT in four dimensions

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...

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

From locally covariant QFT to quantum gravity

Curvature in Noncommutative Geometry

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