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In standard cosmology, the history of the Universe started with an initial big bang singularity where the description by general relativity breaks down. This basic incompleteness of cosmology suggests the need to go beyond general relativity, or beyond matter satisfying the Null Energy Condition, in order to account for the origin of the Universe. An attractive possibility which has gained popularity in recent years is to replace the big bang by a bounce, in which an expanding Universe emerges from a prior period of contraction. This workshop will bring together researchers who have developed different types of bounce scenarios in cosmology. Focus points of the workshop will be comparison of foundations of the different approaches, discussion of conceptual questions, such as whether a classical description of a bounce can make sense or quantum mechanics is essential, and relation to cosmological observations, in particular in light of the usual claim that physics at the big bang is observationally irrelevant.
Perimeter Institute has launched a new program whereby child care support may be available to facilitate your participation in workshops and conferences. Please visit http://www.perimeterinstitute.ca/research/conferences/child-care-support-conference-participants for more information.
- Ivan Agullo, Louisiana State University
- Stephon Alexander, Brown University
- Abhay Ashtekar, Pennsylvania State University
- Aurlien Barrau, Laboratory of Subatomic Physics & Cosmology of Grenoble
- Martin Bojowald, Pennsylvania State University
- Robert Brandenberger, McGill University
- *Claudia de Rham, Imperial College London
- Shane Farnsworth, Albert Einstein Institute
- Jean-Luc Lehners, Albert Einstein Institute
- Ue-Li Pen, CITA
- Mairi Sakellariadou, Kings College London
- Edward Wilson-Ewing, University of New Brunswick
* via teleconference
- Niayesh Afshordi, Perimeter Institute & University of Waterloo
- Ivan Agullo, Louisiana State University
- Stephon Alexander, Brown University
- Abhay Ashtekar, Pennsylvania State University
- Jasdeep Bains, Perimeter Institute
- Aurlien Barrau, Laboratory of Subatomic Physics & Cosmology of Grenoble
- Martin Bojowald, Pennsylvania State University
- Latham Boyle, Perimeter Institute
- Robert Brandenberger, McGill University
- Cliff Burgess, Perimeter Institute & McMaster University
- Sylvain Carrozza, Perimeter Institute
- Linqing Chen, Perimeter Institute
- Bianca Dittrich, Perimeter Institute
- Shane Farnsworth, Albert Einstein Institute
- Job Feldbrugge, Perimeter Institute
- Angelika Fertig, Perimeter Institute
- Marc Geiller, Perimeter Institute
- Ghazal Geshnizjani, Perimeter Institute
- Steffen Gielen, Perimeter Institute & CITA
- Lisa Glaser, Radboud University Nijmegen
- Stephen Green, Perimeter Institute
- Elizabeth Gould, Perimeter Institute
- Daniel Guariento, Perimeter Institute
- Shajidul Haque, University of Cape Town
- Sabine Harribey, ENS de Lyon
- Matthew Johnson, Perimeter Institute & York University
- Darsh Kodwani, CITA
- Jean-Luc Lehners, Albert Einstein Institute
- Ue-Li Pen, CITA
- Andreas Pithis, Kings College London
- Jorge Pullin, Louisiana State University
- Mairi Sakellariadou, Kings College London
- Supranta Sarma Boruah, University of Waterloo
- Laura Sberna, Perimeter Institute
- Barak Shoshany, Perimeter Institute
- Lee Smolin, Perimeter Institute
- Sumati Surya, Raman Research Institute
- Neil Turok, Perimeter Institute
- Francesca Vidotto, Radboud University Nijmegen
- Xin Wang, CITA
- Wolfgang Wieland, Perimeter Institute
- Edward Wilson-Ewing, University of New Brunswick
- Dan Wohns, Perimeter Institute
- I-Sheng Yang, Perimeter Institute & CITA
Monday, June 26, 2017
Time |
Event |
Location |
9:30 – 10:00am |
Registration |
Reception |
10:00 – 10:05am |
Welcome and Opening Remarks |
Bob Room |
10:05 – 10:50am |
Abhay Ashtekar, Pennsylvania State University |
Bob Room |
10:50 – 11:35am |
Ue-Li Pen, CITA |
Bob Room |
11:35 – 12:00pm |
Discussion Session 1 |
Bob Room |
12:00 – 2:00pm |
Lunch |
Bistro – 2nd Floor |
2:00 – 2:45pm |
Robert Brandenberger, McGill University |
Bob Room |
2:45 – 3:30pm |
Edward Wilson-Ewing, University of New Brunswick |
Bob Room |
3:30 – 4:00pm |
Coffee Break |
Bistro – 1^{st} Floor |
4:00 – 6:00pm |
Angelika Fertig, Perimeter Institute |
Sky Room |
Tuesday, June 27, 2017
Time |
Event |
Location |
10:00 – 10:45am |
Claudia de Rham, Imperial College London |
Bob Room |
10:45 – 11:30pm |
Jean-Luc Lehners, Albert Einstein Institute |
Bob Room |
11:30 – 12:00pm |
Discussion Session 3 |
Bob Room |
12:00 – 2:00pm |
Lunch |
Bistro – 2nd Floor |
2:00 – 2:45pm |
Martin Bojowald, Pennsylvania State University |
Bob Room |
2:45 – 3:30pm |
Stephon Alexander, Brown University |
Bob Room |
3:30 – 4:00pm |
Coffee Break |
Bistro – 1^{st} Floor |
4:00 – 6:00pm |
Latham Boyle, Perimeter Institute |
Sky Room |
6:00pm |
Buffet |
Bistro – 1^{st} Floor |
Wednesday, June 28, 2017
Time |
Event |
Location |
10:00 – 10:45am |
Ivan Agullo, Louisiana State University |
Bob Room |
10:45 – 11:30am |
Aurelien Barrau, LPSC |
Bob Room |
11:30 – 12:00pm |
Discussion Session 5 |
Bob Room |
12:00 – 2:00pm |
Lunch |
Bistro – 2nd Floor |
2:00 – 2:45pm |
Mairi Sakellariadou, Kings College London |
Bob Room |
2:45 – 3:30pm |
Shane Farnsworth, Albert Einstein Institute |
Bob Room |
3:30 – 4:00pm |
Coffee Break |
Bistro – 1^{st} Floor |
4:00 – 6:00pm |
Lee Smolin, Perimeter Institute |
Sky Room |
Ivan Agullo, Louisiana State University
Loop Quantum Cosmology, Non-Gaussianity, and CMB anomalies
Loop quantum cosmology has become a robust framework to describe the highest curvature regime of the early universe. In this theory, inflation is preceded by a bounce replacing the big bang singularity. I will summarize the theoretical framework, and explore the corrections to the inflationary predictions for the primordial spectrum of cosmological perturbations that this pre-inflationary, quantum gravity phase of the universe introduces. The impact of the bounce on non-Gaussianity and the exciting relation to the observed large scale anomalies in the CMB will be discussed.
Stephon Alexander, Brown University
A Bouncing Universe approach to Fine Tuning
Abhay Ashtekar, Pennsylvania State University
Bounce in Loop Quantum Cosmology and its Implications
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.
Aurelien Barrau, LPSC
Loop quantum gravity and bounces : cosmology and black hoes
In his talk I will review some recent results concerning the cosmological bounce in loop quantum gravity. In particular I will show how the predicted duration of inflation in affected by the choices of initial conditions, amount of shear and inflaton potential shape. Then I will show how those ideas can be used in black holes physics and comment on the associated phenomenology?
Martin Bojowald, Pennsylvania State University
Space(-time) structure in models of loop quantum gravity
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.
Robert Brandenberger, McGill University
Challenges for Bouncing Cosmologies
I will review various approaches to bouncing cosmologies and will discuss challenges which the different approaches face.
Claudia de Rham, Imperial College London
Unitary Cosmological Bounces
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.
Shane Farnsworth, Albert Einstein Institute
Spinor driven cosmic bounces and their (in)stability
Resolving the big bang singularity with a non-singular classical bounce usually requires the introduction of some sort exotic matter which violates the null-energy condition (NEC), such as a scalar field that undergoes ghost condensation, or models involving Galileon fields. In such models an NEC violating phase is not difficult to achieve on its own, but the situation becomes much more restrictive once observational and stability requirements are taken into consideration. In this talk I discuss whether a more desirable outcome might be achieved by making use of fermionic rather than scalar matter. In particular, I describe bouncing scenarios which arise naturally within the context of Einstein-Cartan-Holst gravity coupled to classical Dirac spinors. As I will show, it is relatively easy to construct backgrounds which not only undergo a bounce, but which also accommodate other interesting dynamics outside the bouncing phase, such as inflation or ekpyrosis. Unfortunately, things work less well when considering perturbations in such bouncing backgrounds as I explain within the context of the simplest models: the comoving curvature perturbation diverges as the moment of NEC violation is approached, and hence the models of greatest interest break down before reaching the bounce.
Jean-Luc Lehners, Albert Einstein Institute
Discussion Session 6
Spinor driven cosmic bounces and their (in)stability
Resolving the big bang singularity with a non-singular classical bounce usually requires the introduction of some sort exotic matter which violates the null-energy condition (NEC), such as a scalar field that undergoes ghost condensation, or models involving Galileon fields. In such models an NEC violating phase is not difficult to achieve on its own, but the situation becomes much more restrictive once observational and stability requirements are taken into consideration.
Cosmological implications of quantum gravity proposals
I will highlight cosmological consequences of Group Field theory Condensate Cosmology and Emergent Gravity on Non-commutative Spaces, two cosmological models based on a top-down and a bottom-up, respectively, approaches to quantum gravity. In particular, I will show that the initial singularity of the standard cosmology is replaced by a bounce, while there is an inflation-like phase with a graceful exit, driven by a purely geometrical mechanism which does not require the introduction of an ad-hoc scalar field.
Loop quantum gravity and bounces : cosmology and black holes
In his talk I will review some recent results concerning the cosmological bounce in loop quantum gravity. In particular I will show how the predicted duration of inflation in affected by the choices of initial conditions, amount of shear and inflaton potential shape. Then I will show how those ideas can be used in black holes physics and comment on the associated phenomenology?
Loop Quantum Cosmology, Non-Gaussianity, and CMB anomalies
Loop quantum cosmology has become a robust framework to describe the highest curvature regime of the early universe. In this theory, inflation is preceded by a bounce replacing the big bang singularity. I will summarize the theoretical framework, and explore the corrections to the inflationary predictions for the primordial spectrum of cosmological perturbations that this pre-inflationary, quantum gravity phase of the universe introduces. The impact of the bounce on non-Gaussianity and the exciting relation to the observed large scale anomalies in the CMB will be discussed.
Discussion Session 4
A Bouncing Universe approach to Fine Tuning
Space(-time) structure in models of loop quantum gravity
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
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
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.
Pages
Scientifc Organziers:
- Steffen Gielen, Perimeter Institute & CITA
- Neil Turok, Perimeter Institute