Talks

6373 - 6384 of 16792 Results

Discussion Session 4

Latham Boyle University of Edinburgh

Job Feldbrugge Perimeter Institute for Theoretical Physics

Neil Turok University of Edinburgh

June 27, 2017

PIRSA:17060104

Cosmology
A Bouncing Universe approach to Fine Tuning

Stephon Alexander Brown University

June 27, 2017

PIRSA:17060103

Cosmology
Space(-time) structure in models of loop quantum gravity

Martin Bojowald Pennsylvania State University

June 27, 2017

PIRSA:17060102

Cosmology
Quantum cosmological instabilities - with and without boundaries

Jean-Luc Lehners Self Employed

June 27, 2017

PIRSA:17060100

Cosmology
Unitary Cosmological Bounces

Claudia de Rham Imperial College London

June 27, 2017

PIRSA:17060099

Cosmology
Discussion Session 2

Angelika Fertig TotalEnergies (France)

Steffen Gielen University of Sheffield

Elizabeth Gould Arthur B. McDonald Canadian Astroparticle Physics Research Institute

June 26, 2017

PIRSA:17060101

Cosmology
Emergent bouncing cosmology from quantum gravity condensates

Edward Wilson-Ewing University of New Brunswick

June 26, 2017

PIRSA:17060098

Cosmology
Challenges for Bouncing Cosmologies

Robert Brandenberger McGill University - Department of Physics

June 26, 2017

PIRSA:17060096

Cosmology
Observable Consequences of a Bounce

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)

June 26, 2017

PIRSA:17060097

Cosmology
Bounce in Loop Quantum Cosmology and its Implications

Abhay Ashtekar Pennsylvania State University

June 26, 2017

PIRSA:17060095

Cosmology
Welcome and Opening Remarks

Steffen Gielen University of Sheffield

Neil Turok University of Edinburgh

June 26, 2017

PIRSA:17060094

Cosmology
The Universal Renormalization Group Machine - 2

Frank Saueressig Radboud Universiteit Nijmegen

June 23, 2017

PIRSA:17060092

Quantum Gravity

Discussion Session 4

Latham Boyle University of Edinburgh

Job Feldbrugge Perimeter Institute for Theoretical Physics

Neil Turok University of Edinburgh

June 27, 2017

PIRSA:17060104

Cosmology
A Bouncing Universe approach to Fine Tuning

Stephon Alexander Brown University

June 27, 2017

PIRSA:17060103

Cosmology
Space(-time) structure in models of loop quantum gravity

Martin Bojowald Pennsylvania State University

June 27, 2017

PIRSA:17060102

Cosmology

Loop quantum gravity has suggested modifications of the dynamics of cosmological models that could lead to a bounce at large curvature. However, the same modifications may alter the gauge structure of the theory, which is related to the structure of space-time. In a large class of examples the space-time structure has been derived and shown to imply signature change just in the bounce region. The picture of a cyclic universe with a deterministic bounce then has to be replaced by the scenario of a non-singular beginning some finite time ago.
Quantum cosmological instabilities - with and without boundaries

Jean-Luc Lehners Self Employed

June 27, 2017

PIRSA:17060100

Cosmology

The big bang singularity might be avoided by replacing it with a theory of initial conditions, or by considering a bounce from an earlier contracting phase. I will describe how both proposals can run into difficulties with instabilities when the spacetime must be treated semi-classically (i.e. when bounces occur due to a quantum tunneling transition rather than as classically non-singular solutions). The absence of such instabilities places new restrictions on the available theories, implying a selection criterion whose consequences remain to be explored.
Unitary Cosmological Bounces

Claudia de Rham Imperial College London

June 27, 2017

PIRSA:17060099

Cosmology

A non-singular cosmological bounce in the Einstein frame can only take place if the Null Energy Condition (NEC) is violated. I will explore the constraints imposed by demanding tree level unitarity on a cosmological background in single scalar field theories before focusing on the explicit constraints that arise in P(X) theories. In that context, perturbative unitarity makes it impossible for the NEC violation to occur within the region of validity of the effective field theory but I will show explicitly how unitarity may be restored by involving irrelevant operators that arise at a higher scale.
Discussion Session 2

Angelika Fertig TotalEnergies (France)

Steffen Gielen University of Sheffield

Elizabeth Gould Arthur B. McDonald Canadian Astroparticle Physics Research Institute

June 26, 2017

PIRSA:17060101

Cosmology
Emergent bouncing cosmology from quantum gravity condensates

Edward Wilson-Ewing University of New Brunswick

June 26, 2017

PIRSA:17060098

Cosmology

I will explain how cosmological dynamics emerge from the hydrodynamics of isotropic group field theory condensate states in the Gross-Pitaevskii approximation. The correct Friedmann equations are recovered in the classical limit for some choices of the parameters in the action for the group field theory, and quantum gravity corrections arise in the high-curvature regime causing a bounce which generically resolves the big-bang and big-crunch singularities.
Challenges for Bouncing Cosmologies

Robert Brandenberger McGill University - Department of Physics

June 26, 2017

PIRSA:17060096

Cosmology

I will review various approaches to bouncing cosmologies and will discuss challenges which the different approaches face.
Observable Consequences of a Bounce

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)

June 26, 2017

PIRSA:17060097

Cosmology

I discuss potentially observable signatures of scalar and tensor decaying modes, which do not exist in inflation, and could be a probe of a bouncing universe.
Bounce in Loop Quantum Cosmology and its Implications

Abhay Ashtekar Pennsylvania State University

June 26, 2017

PIRSA:17060095

Cosmology

There is a huge body of work in Loop Quantum Cosmology comprising of several thousand journal articles. I will provide an overview of conclusions, focusing on the difficult conceptual and mathematical issues that accompany the notion of a bounce and opening the way for phenomenological implications that will be discussed by Ivan Agullo.
Welcome and Opening Remarks

Steffen Gielen University of Sheffield

Neil Turok University of Edinburgh

June 26, 2017

PIRSA:17060094

Cosmology
The Universal Renormalization Group Machine - 2

Frank Saueressig Radboud Universiteit Nijmegen

June 23, 2017

PIRSA:17060092

Quantum Gravity

Functional renormalization group techniques based on Wetterichs equation provide a powerful tool for studying the properties of gravity in the quantum regime and its connection to the observable low-energy world. Explicit computations in this framework require the evaluation of functional traces over operator-valued functions. In these lectures I will give a pedagogical introduction to the Universal Renormalization Group Machine, a combinatorial algorithm which allows evaluating such traces in a systematic way. Moreover, I will discuss flow equations for “composite operators” which may pave the route towards developing a microscopic description of quantum spacetime within the Asymptotic Safety approach.

Title	Date	Collection	Type	Info
Discussion Session 4	2017‑06‑27	Bounce Scenarios in Cosmology	Conference	View details
A Bouncing Universe approach to Fine Tuning	2017‑06‑27	Bounce Scenarios in Cosmology	Conference	View details
Space(-time) structure in models of loop quantum gravity	2017‑06‑27	Bounce Scenarios in Cosmology	Conference	View details
Quantum cosmological instabilities - with and without boundaries	2017‑06‑27	Bounce Scenarios in Cosmology	Conference	View details
Unitary Cosmological Bounces	2017‑06‑27	Bounce Scenarios in Cosmology	Conference	View details
Discussion Session 2	2017‑06‑26	Bounce Scenarios in Cosmology	Conference	View details
Emergent bouncing cosmology from quantum gravity condensates	2017‑06‑26	Bounce Scenarios in Cosmology	Conference	View details
Challenges for Bouncing Cosmologies	2017‑06‑26	Bounce Scenarios in Cosmology	Conference	View details
Observable Consequences of a Bounce	2017‑06‑26	Bounce Scenarios in Cosmology	Conference	View details
Bounce in Loop Quantum Cosmology and its Implications	2017‑06‑26	Bounce Scenarios in Cosmology	Conference	View details
Welcome and Opening Remarks	2017‑06‑26	Bounce Scenarios in Cosmology	Conference	View details
The Universal Renormalization Group Machine - 2	2017‑06‑23	Making Quantum Gravity Computable	Conference	View details

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