Bounce Scenarios in Cosmology

Conference Date: 
Monday, June 26, 2017 (All day) to Wednesday, June 28, 2017 (All day)
Scientific Areas: 
Cosmology

 

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
Bounce in Loop Quantum Cosmology and its Implications

Bob Room

10:50 – 11:35am

Ue-Li Pen, CITA
Observable Consequences of a Bounce

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
Challenges for Bouncing Cosmologies

Bob Room

2:45 – 3:30pm

Edward Wilson-Ewing, University of New Brunswick
Emergent bouncing cosmology from quantum gravity condensates

Bob Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 6:00pm

Angelika Fertig, Perimeter Institute
Steffen Gielen, Perimeter Institute & CITA
Elizabeth Gould, Perimeter Institute
Discussion Session 2

Sky Room

 

Tuesday, June 27, 2017

Time

Event

Location

10:00 – 10:45am

Claudia de Rham, Imperial College London
Unitary Cosmological Bounces

Bob Room

10:45 – 11:30pm

Jean-Luc Lehners, Albert Einstein Institute
Quantum cosmological instabilities - with and without boundaries

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

Bob Room

2:45 – 3:30pm

Stephon Alexander, Brown University
A Bouncing Universe approach to Fine Tuning

Bob Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 6:00pm

Latham Boyle, Perimeter Institute
Job Feldbrugge, Perimeter Institute
Neil Turok, Perimeter Institute
Discussion Session 4

Sky Room

6:00pm

Buffet

Bistro – 1st Floor

 

Wednesday, June 28, 2017

Time

Event

Location

10:00 – 10:45am

Ivan Agullo, Louisiana State University
Loop Quantum Cosmology, Non-Gaussianity, and CMB anomalies

Bob Room

10:45 – 11:30am

Aurelien Barrau, LPSC
Loop quantum gravity and bounces : cosmology and black hoes

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
Cosmological implications of quantum gravity proposals

Bob Room

2:45 – 3:30pm

Shane Farnsworth, Albert Einstein Institute
Spinor driven cosmic bounces and their (in)stability

Bob Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 6:00pm

Lee Smolin, Perimeter Institute
Discussion Session 6

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

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.
 
Ue-Li Pen, CITA
 
Observable Consequences of a Bounce
 
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.
 
Mairi Sakellariadou, Kings College London
 
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. 
 
Edward Wilson-Ewing, University of New Brunswick
 
Emergent bouncing cosmology from quantum gravity condensates
 
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.

 

 

Wednesday Jun 28, 2017
Speaker(s): 
Collection/Series: 
Scientific Areas: 

 

Wednesday Jun 28, 2017
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

 

Wednesday Jun 28, 2017
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

 

Wednesday Jun 28, 2017
Speaker(s): 

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?

Collection/Series: 
Scientific Areas: 

 

Wednesday Jun 28, 2017
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

 

Tuesday Jun 27, 2017
Collection/Series: 
Scientific Areas: 

 

Tuesday Jun 27, 2017
Speaker(s): 
Collection/Series: 
Scientific Areas: 

 

Tuesday Jun 27, 2017
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

 

Tuesday Jun 27, 2017
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

 

Tuesday Jun 27, 2017
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

Pages

Scientifc Organziers:

  • Steffen Gielen, Perimeter Institute & CITA
  • Neil Turok, Perimeter Institute