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Search results in General Relativity & Quantum Cosmology from PIRSA

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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
A non-commuting stabilizer formalism

Xiaotong Ni Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
April 09, 2014

PIRSA:14040136
Quantum Physics

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 University of Toronto
March 27, 2014

PIRSA:14030115
General Relativity & Quantum Cosmology
Bungee jumping of black holes in AdS universe
March 27, 2014

PIRSA:14030108
General Relativity & Quantum Cosmology
Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space

Andrew Strominger Harvard University
March 13, 2014

PIRSA:14030087
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
Sequestering Lorentz violation in the Lifshitz sector

Maxim Pospelov University of Minnesota
March 06, 2014

PIRSA:14030092
General Relativity & Quantum Cosmology
Nonlocal cosmology

Richard Woodard University of Florida
February 27, 2014

PIRSA:14020137
General Relativity & Quantum Cosmology
À la recherche du temps perdu - Templeton Frontiers Colloquia

Flavio Mercati University of Naples Federico II
February 26, 2014

PIRSA:14020100
General Relativity & Quantum Cosmology
Quantum Raychaudhuri equation

Saurya Das University of Lethbridge
February 20, 2014

PIRSA:14020130
General Relativity & Quantum Cosmology

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.
A non-commuting stabilizer formalism

Xiaotong Ni Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
April 09, 2014

PIRSA:14040136
Quantum Physics

General Relativity & Quantum Cosmology
We propose a non-commutative extension of the Pauli stabilizer formalism. The aim is to describe a class of many-body quantum states which is richer than the standard Pauli stabilizer states. In our framework, stabilizer operators are tensor products of single-qubit operators drawn from the group {\alpha I, X,S}, where \alpha=e^{i\pi/4} and S=diag(1,i). We provide techniques to efficiently compute various properties, related to e.g. bipartite entanglement, expectation values of local observables, preparation by means of quantum circuits, parent Hamiltonians etc. We also highlight significant differences compared to the Pauli stabilizer formalism. In particular we give examples of states in our formalism which cannot arise in the Pauli stabilizer formalism, such as topological models that supports non-abelian anyons. This is a joint work with O. Buerschaper and M. van den Nest.
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 University of Toronto
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.
Bungee jumping of black holes in AdS universe
March 27, 2014

PIRSA:14030108
General Relativity & Quantum Cosmology
C-metric describes uniformly accelerated black holes. We will review a global structure of these solutions especially in Lambda<0 context. It turns out that for an acceleration larger than the cosmological one the metric describes pairs of black holes "bungee jumping" into spacetime from AdS infinity.
Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space

Andrew Strominger Harvard University
March 13, 2014

PIRSA:14030087
General Relativity & Quantum Cosmology
We argue that the infinite-dimensional BMS symmetry discovered by Bondi et. al in the 60s provides an exact symmetry of the quantum gravity S-matrix. The Ward identity of this symmetry is shown to be precisely Weinberg's soft graviton theorem, also discovered in the 60s. A parallel infinite-dimensional symmetry is found to be generated in nonabelian gauge theories by gauge transformations which go to an angle-dependent finite constant at null infinity. The Ward identity of this symmetry is shown to be the soft gluon theorem.
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.
Sequestering Lorentz violation in the Lifshitz sector

Maxim Pospelov University of Minnesota
March 06, 2014

PIRSA:14030092
General Relativity & Quantum Cosmology
Horava's proposal to use Lifshitz propagators for gravitons above certain energy scales may provide a viable theory of quantum gravity without further need of UV completion. In my talk, I will address the question of whether the complete lack of Lorentz invariance above a certain energy scale is a big problem for any realistic construction. I will argue that it is not, provided that the onset of Lifshitz scaling for gravitons occurs at momentum scale much lower than the Planck mass. I will also discuss consequences of combining Lifshitz gravity and supersymmetric matter sector.
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.
À la recherche du temps perdu - Templeton Frontiers Colloquia

Flavio Mercati University of Naples Federico II
February 26, 2014

PIRSA:14020100
General Relativity & Quantum Cosmology
Augustine of Hippo declared he knew what time is until someone asked him. After 16 centuries we still largely ignore the true essence of time, but we made definite progress in studying its properties. The most striking, and somewhat intuitively (and tragically) obvious one is the irreversibility of its flow. And yet, our fundamental theories are time-reversal invariant, they do not distinguish between past and future. This is usually accounted for by assuming an immensely special initial condition of the Universe, dressed with statistical arguments. In this talk, I will show how an irreversible behaviour, and with it a growth of complexity and information, can emerge from time-reversal invariant laws, without assuming any special initial condition and without thermodynamical arguments. This phenomenon is present in General Relativity, our most advanced theory of the Universe. This irreversibility will also allow me to propose a solution of another puzzle associated with time, namely the incompatibility between the quantum and the general-relativistic notions of time.
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

Title	Date	Collection	Type	Info
Universal problems	2014‑04‑17	Quantum Gravity	Scientific Series	View details
Quantum cosmology in Lorentz-violating gravity	2014‑04‑10	Quantum Gravity	Scientific Series	View details
A non-commuting stabilizer formalism	2014‑04‑09	Perimeter Institute Quantum Discussions	Scientific Series	View details
Quantum Gravity, Trees, and Polynomials	2014‑04‑03	Quantum Gravity	Scientific Series	View details
Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes	2014‑03‑27	Quantum Gravity	Scientific Series	View details
Bungee jumping of black holes in AdS universe	2014‑03‑27	Strong Gravity	Scientific Series	View details
Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space	2014‑03‑13	Strong Gravity	Scientific Series	View details
A one-dimensional action for simplicial gravity in three dimensions	2014‑03‑06	Quantum Gravity	Scientific Series	View details
Sequestering Lorentz violation in the Lifshitz sector	2014‑03‑06	Strong Gravity	Scientific Series	View details
Nonlocal cosmology	2014‑02‑27	Quantum Gravity	Scientific Series	View details
À la recherche du temps perdu - Templeton Frontiers Colloquia	2014‑02‑26	Colloquium	Scientific Series	View details
Quantum Raychaudhuri equation	2014‑02‑20	Quantum Gravity	Scientific Series	View details

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Format results

Universal problems

Quantum cosmology in Lorentz-violating gravity

A non-commuting stabilizer formalism

Quantum Gravity, Trees, and Polynomials

Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes

Bungee jumping of black holes in AdS universe

Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space

A one-dimensional action for simplicial gravity in three dimensions

Sequestering Lorentz violation in the Lifshitz sector

Nonlocal cosmology

À la recherche du temps perdu - Templeton Frontiers Colloquia

Quantum Raychaudhuri equation

Universal problems

Quantum cosmology in Lorentz-violating gravity

A non-commuting stabilizer formalism

Quantum Gravity, Trees, and Polynomials

Possible Astrophysical Observables of Quantum Gravity Effects near Black Holes

Bungee jumping of black holes in AdS universe

Asymptotic Symmetries of Gauge and Gravity Theories in Minkowski Space

A one-dimensional action for simplicial gravity in three dimensions

Sequestering Lorentz violation in the Lifshitz sector

Nonlocal cosmology

À la recherche du temps perdu - Templeton Frontiers Colloquia

Quantum Raychaudhuri equation