Renormalization Group Approaches to Quantum Gravity

Conference Date: 
Tuesday, April 22, 2014 (All day) to Friday, April 25, 2014 (All day)
Scientific Areas: 
Quantum Gravity

 

The Renormalization Group provides a unifying tool to study quantum gravity approaches: Bridging the gap between microscopic and macroscopic scales, it can be used in two directions in quantum gravity: On the one hand, following the Renormalization Group flow towards high momentum scales allows us to test the consistency of the asymptotic safety scenario for quantum gravity. On the other hand, following the flow towards the infrared, allows us to check whether a viable semiclassical limit emerges from a microscopic model of quantum gravity, such as a spin foam model. Very much in the spirit of condensed-matter models, fixed points of the Renormalization Group flow can provide a continuum limit in approaches such as Causal Dynamical Triangulations, spin foams, matrix and tensor models.

This workshop will for the first time bring together researchers working on different models of quantum gravity, who use the Renormalization Group in different forms. We will discuss conceptual as well as more technical questions, and establish a new dialogue between different quantum gravity approaches.

Sponsorship for this conference has been provided by:

 

 

Jan Ambjorn, Niels Bohr Institute
Benjamin Bahr, University of Hamburg
Dario Benedetti, Albert Einstein Institute
Alfio Bonanno, National Institute for Astrophysics
Sylvain Carozza, CPT Marseille
Joshua Cooperman, Radboud University Nijmegen
Bianca Dittrich, Perimeter Institute
John Donoghue, University of Massachusetts
Astrid Eichhorn, Perimeter Institute

Zheng-Cheng Gu, Perimeter Institute
Razvan Gurau, Université Paris-Sud XI Orsay
Petr Horava, Universityof California, Berkeley
Tim Koslowski, University of New Brunswick
Daniel Litim, University of Sussex
Renate LollRadboud University Nijmegen
Mercedes Martin Benito, Radboud University Nijmegen
Tim Morris, University of Southampton
Daniele Oriti, Albert Einstein Institute
Jan Pawlowski, University of Heidelberg
Martin Reuter, Johannes Gutenberg University
Vincent RivasseauUniversité Paris-Sud XI Orsay
James Ryan, Albert Einstein Institute
Dine Ousmane Samary, Perimeter Institute
Frank SaueressigRadboud University Nijmegen
Lee Smolin, Perimeter Institute
Simone Speziale, CPT Marseille
Kellogg Stelle, Imperial College, London

 

 

  • Jan Ambjorn, Niels Bohr Institute
  • Benjamin Bahr, University of Hamburg
  • Andrzej Banburski, Perimeter Institute
  • Aristide Baratin, Centre de Physique Theorique, Ecole Polytechnique
  • Jacob Barnett, Perimeter Institute
  • Dario Benedetti, Albert Einstein Institute
  • Alfio Bonanno, National Institute for Astrophysics
  • Sylvain Carozza, CPT Marseille
  • Joshua Cooperman, Radboud University Nijmegen
  • Bianca Dittrich, Perimeter Institute
  • Pietro Dona, SISSA
  • John Donoghue, University of Massachusetts
  • Maite Dupuis, University of Erlangen-Nuernberg
  • Astrid Eichhorn, Perimeter Institute
  • Laurent Freidel, Perimeter Institute
  • Marc Geiller, Pennsylvania State University
  • Florian Girelli, University of Waterloo
  • Lisa Glaser, Niels Bohr Institute
  • Zheng-Cheng Gu, Perimeter Institute
  • Razvan Gurau, Université Paris-Sud XI Orsay
  • Hal HaggardCentre de Physique Theorique de Luminy
  • Petr Horava, University of Clifornia, Berkeley
  • Tim Koslowski, University of New Brunswick
  • Stefan Lippoldt, University of Jena
  • Daniel Litim, University of Sussex
  • Renate Loll, Radboud University Nijmegen
  • Mercedes Martin Benito, Radboud University Nijmegen
  • Tim Morris, University of Southampton
  • Daniele Oriti, Albert Einstein Institute
  • Carlo Pagani, SISSA
  • Jan Pawlowski, University of Heidelberg
  • Roberto Percacci, SISSA
  • Luis Pires, Radboud University Nijmegen
  • Martin Reuter, Johannes Gutenberg University
  • Vincent Rivasseau, Université Paris-Sud XI Orsay
  • James Ryan, Albert Einstein Institute
  • Dine Ousmane Samary, Perimeter Institute
  • Frank Saueressig, Radboud University Nijmegen
  • Giuseppe Sellaroli, University of Waterloo
  • Lee Smolin, Perimeter Institute
  • Simone Speziale, CPT Marseille
  • Sebastian Steinhaus, Perimeter Institute
  • Kellogg Stelle, Imperial College, London
  • Dejan Stojkovic, University of Buffalo
  • Tomasz Trzesniewski, University of Wroclaw
  • Gian Paolo Vacca, National Institute for Nuclear Physics
  • Wolfgang Wieland, Pennsylvania State University

Renormalization Group Approaches to Quantum Gravtiy

Tuesday, April 22, 2014

Time

Event

Location

8:30 – 9:00am

Registration

Reception

9:00 – 9:10am

Welcome and Opening Remarks

Bob Room

9:10 – 10:10am

Overview Asymptotic Safety

Tim Morris, University of Southampton
Recent developments in asymptotic safety:
tests and properties

Bob Room

10:10 – 11:10am

Overview Causal Dynamic Triangulations

Renate Loll, Radboud University Nijmegen
What you always wanted to know about CDT, but did not have time to read about in our papers

Bob Room

11:10 – 11:40am

Break

Bistro – 1st Floor

11:40 – 11:50am

Conference Photo

Atrium

11:50 – 12:40pm

Overview Tensor Track

Razvan Gurau, Université Paris-Sud XI Orsay
Tensor models in the large N limit

Bob Room

12:40 – 2:30pm

Lunch

Bistro – 2nd Floor

2:30 – 3:20pm

Overview Renormalization in Group Field Theories

Daniele Oriti, Albert Einstein Institute
Motivations and a brief review

Bob Room

3:20 – 4:20pm

Overview Renormalization in Spin Foams

Bianca Dittrich, Perimeter Institute
Quantum Spacetime Engineering

Bob Room

4:20 – 4:50pm

Break

Bistro – 1st Floor

4:50 – 6:00pm

Challenge Talks

Lee Smolin, Perimeter Institute &
Simone Speziale, CPT Marseille
What are the most pressing open questions in the application of the RG to gravity?

Bob Room

 

Wednesday, April 23, 2014

Poster Session opens Wednesday morning

Time

Event

Location

9:00 – 9:40am

 

9:40 – 10:20am

Connecting the RG in gravity to phenomenology

John Donoghue, University of Massachusetts
Perturbative quantum gravity calculations
and running couplings

Daniel Litim, University of Sussex
TBA

 

 

Bob Room

 

 

10:20 – 11:00am

Break

Atrium

11:00 – 11:40am
 

11:40 – 12:00pm

Connecting the RG in gravity to phenomenology cont.

Alfio Bonanno, INAF
Confronting Asymptotically Safe Inflation with Planck data

Kellogg Stelle, Imperial College, London
TBA

Bob Room

12:00 – 12:40pm

Discussion of morning talks

(How) can we extract phenomenological consequences of the RG flow in gravity?
What is the role of Lorentzian signature in this?

Bob Room

12:40 – 2:00pm

Lunch

Bistro – 2nd Floor

2:00 - 3:30pm

Perimeter Institute Colloquium
Krzysztof Meissner, University of Warsaw
Conformal Standard Model

Theater

 

3:30 – 4:10pm
 

4:10 – 4:50pm

Connections between methods and results from different approaches

Tim Koslowski, University of New Brunswick
Asymptotic safety in a pure matrix model

Jan Ambjorn, Niels Bohr Institute
RG flow in CDT

Bob Room

4:50 - 5:10pm Break Atrium

5:10 – 5:50pm

Connections between methods and results from different approaches cont.

Mercedes Martin-Benito, Radboud University Nijmegen
Refinement limit of quantum group spinnets

Bob Room

5:50 – 6:40pm

Discussion

Is there a relation between some approaches?
What are the tools to uncover it?
Can methods be carried over from one approach to the other, to make progress?

Bob Room

6:45pm

Banquet

Bistro – 2nd Floor

 

 

Thursday, April 24, 2014

Time

Event

Location

 

9:00 – 9:40am

9:40 – 10:20am

 

Renormalization Group in gravity and symmetries

Zheng-Cheng Gu, Perimeter Institute
TBA

Jan Pawlowski, University of Heidelberg
Global flows in quantum gravity

Bob Room

10:20 – 11:00am

Break

Atrium

11:00 – 11:40am

Renormalization Group in gravity and symmetries cont.

Benjamin Bahr, University of Hamburg
On background-independent renormalization in state-sum model

Bob Room

 

11:40 – 12:00pm

Discussion

What is the meaning of the Renormalization Group scale in a diffeomorphism invariant theory?

 

Bob Room

12:00 – 12:30pm

Discussion

What is the role of the Planck length in RG approaches
to gravity?
How does a minimal length manifest itself in RG approaches to gravity?

Bob Room

12:30 – 2:30pm

Lunch

Bistro – 2nd Floor

2:30 – 3:10pm

 

3:10 – 3:50pm

Lorentz invariance and the RG flow in gravity

Petr Horava, University of California, Berkeley
Phases of Gravity

Dario Beneditti, Albert Einstein Institute
One-loop renormalization in a toy model of Horava-Lifshitz gravity

 

Bob Room

 

3:50 – 4:30pm

Break

Atrium

4:30 – 5:10pm

Lorentz invariance and the RG flow in gravity cont.

Frank Saueressig, Radboud University Nijmegen
Gravitational RG flows on foliated spacetimes

 

Bob Room

5:10 – 6:00pm

Discussion

What are the mechanisms for restoration of symmetry during 
the RG flow?
What are the prospects for a restoration of Lorentz invariance
at low energies?

Bob Room

6:00pm

Pub Night

Bistro

 

Friday, April 25, 2014

Time

Event

Location

9:00 – 9:40am

 

9:40 – 10:20am

What are the fundamental gravitational degrees of freedom?

Martin Reuter, Johannes Gutenberg-Universität Mainz
The Asymptotic Safety Program:
New results and an inconvenient truth

Astrid Eichhorn, Perimeter Institute
Why matter matters in quantum gravity

Bob Room

10:20 – 11:00am

Break

Atrium

 

11:00 – 11:40am

What are the fundamental gravitational degrees of freedom?cont.

Joshua Cooperman, Radboud University Nijmegen
Renormalization of entanglement entropy and the
gravitational effective action

 

Bob Room

11:40 – 12:20pm

Discussion

What are the degrees of freedom we should use in a gravitational path integral?
What are mathematical and phenomenological consequences
of using different degrees of freedom?

Bob Room

12:20 – 2:30pm

Lunch

Bistro – 2nd Floor

 

2:30 – 3:10pm
 

3:10 – 3:50pm

Renormalization Group in spacetime vs. group space

Sylvain Carrozza, CPT Marseille
Renormalization group approach to 3d group field theory

Vincent Rivasseau, Université Paris-Sud XI Orsay
Renormalizable tensorial group field theories

 

Bob Room

3:50 – 4:30pm

Break

Atrium

 

4:30 – 5:10pm

Renormalization Group in spacetime vs. group space cont.

James Ryan, Albert Einstein Institute
Double scaling in tensor models

 

Bob Room

 

5:10 – 6:00pm

Discussion

What is the meaning of asymptotic freedom or asymptotic
safety in group space?

 

Bob Room

6:30pm

Casual Dinner – Details TBA

Offsite

 

 

Jan Ambjorn, Niels Bohr Institute

RG flow in CDT

An attempt is made to define "lines of contant physics" in CDT and relate the corresponding picture to  non-trivial UV fixed points as they appear in the asymptotic safety scenario.

Benjamin Bahr, University of Hamburg

On background-independent renormalization in state-sum models

In this talk we discuss some notion of coarse graining in state-sums, most notably a class of spin foam models in their holonomy representations. We discuss the notion of scale in this context, and how diffeomorphism-invariance ties into the existence of a continuum limit. We close with an example and muse about the interplay between diffeomorphism-invariance and non-renormalizability. 

Dario Benedetti, Albert Einstein Institute

One-loop renormalization in a toy model of Horava-Lifshitz gravity

I will present some recent results on the UV properties of a toy model of Horava-Lifshitz gravity in 2+1 dimensions.  In particular, I will illustrate some details of a one-loopcalculation, leading to beta functions for the running couplings. The renormalization group flow obtained in such way shows that Newton's constant is asymptotically free. However, the DeWitt supermetric approaches its Weyl invariant form with the same speed and the effective interaction coupling of the scalar degree of freedom remains constant along the flow. I will discuss some general lesson that we can learn from these results.

Alfio Bonanno, INAF

Confronting Asymptotically Safe Inflation with Planck data

Sylvain Carrozza, CPT Marseille

Renormalization group approach to 3d group field theory

I will start with a brief overview of tensorial group field theories with gauge invariant condition and their relation to spin foam models. The rest of the talk will be focused on the SU(2) theory in dimension 3, which is related to Euclidean 3d quantum gravity and has been proven renormalizable up to order 6 interactions. General renormalization group flow equations will be introduced, allowing in particular to understand the behavior of the relevant couplings in the neighborhood of the Gaussian fixed point. I will close with preliminary investigations about the existence of a non-trivial fixed point. 

Joshua Cooperman, Radboud University Nijmegen

Renormalization of entanglement entropy and the gravitational effective action

The entanglement entropy associated with a spatial boundary in quantum field theory is ultraviolet divergent, its leading term being proportional to the area of the boundary. Callan and Wilczek proposed a geometrical prescription for computing this entanglement entropy as the response of the gravitational effective action to a conically singular metric perturbation. I argue that the Callan-Wilczek prescription is rigorously justified at least for a particular class of quantum states each expressible as a Euclidean path integral. I then show that the entanglement entropy is rendered ultraviolet finite by precisely the counterterms required to cancel the ultraviolet divergences in the gravitational effective action. In particular, the leading contribution to the entanglement entropy is given by the renormalized Bekenstein-Hawking formula. These results apply to a general quantum field theory coupled to a fixed background metric, holding for arbitrary entangling surfaces with vanishing extrinsic curvature in any dimension, to all orders in perturbation theory in the quantum fields, and for all ultraviolet divergent terms in the entanglement entropy. I also reconcile these results on the entanglement entropy with the existing literature, compare them to the Wald entropy, and speculate on their interpretation and implication.

Bianca Dittrich, Perimeter Institute

Quantum Spacetime Engineering

Given (a set of) fundamental models of quantum space time, for instance spin foam models, we aim to understand the large scale physics encoded in these fundamental models. Renormalization and coarse graining address this issue and help to understand how large scale physics depends on parameters in the fundamental models.
 
I will review recent work on coarse graining and renormalization of spin foam and analogue models, revealing possible large scale phases, depending on parameters of the microscopic models. I will explain how these phases are connected to topological field theories and possible vacua for the theory of quantum gravity, e.g. loop quantum gravity. I outline how these different vacua are connected to different representations of the observable algebra, that is different Hilbert spaces,  and how this allows to expand the theory around different vacuum states.

John Donoghue, University of Massachusetts

Perturbative quantum gravity calculations and running couplings

We know how to make perturbative calculations in quantum gravity using the framework of effective field theory. I will describe the basics of the effective field theory treatment and look at several calculations. There are obstacles to describing these with running coupling constants. Finally, I will do my best to try to connect these with the Asymptotic Safety program.

Astrid Eichhorn, Perimeter Institute

Why matter matters in quantum gravity

I will argue that a fundamental theory of quantum gravity that is applicable to our universe must include matter degrees of freedom. In my talk I will focus on the option that these are fundamental, in contrast to low-energy effective, degrees of freedom, and must thus be included in the microscopic dynamics of spacetime.
I will present evidence that dynamical Standard Model matter is compatible with asymptotically safe quantum gravity, while several "Beyond Standard Model" scenarios are disfavored. I will also discuss how the coupling to matter opens a window into the observational quantum gravity regime.

Razvan Gurau, Université Paris-Sud XI Orsay

Tensor Models in the Large N limit

Tensor models generalize matrix models and provide a framework for the study of random geometries in arbitrary dimensions. Like matrix models they support a 1/N expansion, where N is the size of the tensor, with an analytically controlled large N limit. In this talk I will present some recent results in this field and I will discuss their implications for quantum gravity.

Petr Horava, University of California, Berkeley

Phases of Gravity

Quantum gravity with anisotropic scaling exhibits a rich structure of phases  and phase transitions,  dominated by multicritical behavior dependent on the  spacetime dimension and the dynamical critical exponent.  I will discuss some  features of this phase structure, as well as its similarities and differences in  comparison to the CDT approach to quantum gravity.

Tim Koslowski, University of New Brunswick

Asymptotic safety in a pure matrix model

The connection between two-dimensional Euclidean gravity and pure matrix models has lead to may fundamental insights about quantum gravity and string theory. The pure matrix model is thus a blueprint for the connection between discrete models and Euclidean quantum gravity. I will report on work with Astrid Eichhorn in which this "blueprint" model is investigated with the functional renormalization group. In this model, I will discuss the questions: "What is a possible meaning of asymptotic safety in a discrete model?" and "Is it possible to apply the FRGE to tensor models?

Renate Loll, Radboud University Nijmegen

What you always wanted to know about CDT, but did not have time to read about in our papers

I will review the approach of Causal Dynamical Triangulations to nonperturbative quantum gravity, high-lighting some frequently mis- or ununderstood features, emphasizing recent developments and discussing some interesting open issues.

Mercedes Martin-Benito, Radboud University Nijmegen

Refinement limit of quantum group spinnets

The many-building-blocks limit of spin foam models remains to be an open question. The complexity of these models makes the analysis of their possible continuum phases a very difficult task. In the last years progress in this direction has been made by considering simplified, yet featured-rich, analog models to spin foams, the so-called spin net models. These models retain the main dynamical ingredient of spin foams, namely the simplicity constraints. In this talk we will introduce spin net models based on the quantum group SU(2)_q, and we will review the use of tensor network renormalization group techniques to study their coarse graining. We will analyze the resulting phase diagram, which interestingly displays a rich structure of fixed points. Furthermore we will discuss the relation of spin nets with spin foams.

Tim Morris, University of Southampton

Recent developments in asymptotic safety: tests and properties

The talk will review recent tests of the asymptotic safety conjecture within functional renormalisation group studies and progress in understanding the properties that such a fixed point would have.

Daniele Oriti, Albert Einstein Institute

Renormalization of group field theories: motivations and a brief review

Group field theories are tensorial models enriched with group-theoretic data in order to define proper field theories of quantum geometry. They can be understood as a second quantised (Fock space) reformulation of loop quantum gravity kinematics and dynamics. The renormalization group provides, as a in any quantum field theory, a key tool to select well-defined models, to unravel the impact of quantum effects on the dynamics across different scales, and to study the continuum limit. Beside introducing the general formalism and clarifying the relation to other approaches, we will motivate the  renormalisation group analysis of group field theories and review recent developments in this direction.

Jan Pawlowski, University of Heidelberg

Global flows in quantum gravity

In this talk I present recent work on complete UV-IR flows for the fully momentum-dependent propagator, RG-consistent vertices, Newtons coupling and the cosmological constant. For the first time, a global phase diagram is obtained where the non-Gaussian ultraviolet fixed point of asymptotic safety is connected via smooth trajectories to an infrared fixed point with classical scaling. Physics implications as well as the extension to gauge-matter-gravity systems are discussed.

Martin Reuter, Johannes Gutenberg-Universität Mainz

The Asymptotic Safety Program: new results and an inconvenient truth

We briefly review the various components and their conceptual status of the full Asymptotic Safety Program which aims at finding a nonperturbative infinite-cutoff limit of a regularized functional integral for a quantum field theory of gravity. It is explained why in the continuum formulation based on the Effective Average Action the key requirement of background independence unavoidably results in a "bi-metric" framework, and recent results on truncated RG flows of bi-metric actions are presented. They suggest that the next generation of truncations that must be explored should be of bi-metric type. As an application, a method of characterizing and counting physical states is shown to arise.

Vincent Rivasseau, Université Paris-Sud XI Orsay

Renormalizable Tensorial Group Field Theories

We give an overview of a new category of perturbatively renormalizable models for quantum gravity. Using tensorial invariant interactions and a regularized propagator for scale analysis, they perform a synthesis between group field theories and dynamical triangulations. They realize the 1/N expansion of tensor models  dynamically via a renormalization group flow which is typically asymptotically free.

James Ryan, Albert Einstein Institute

Double scaling in tensor models

I present recent work on the double scaling limit of random tensor models through the analysis of their Schwinger-Dyson equations.  This study exemplifies their potential for probing the continuum phase structure of these theories.  

Frank Saueressig, Radboud University Nijmegen

Gravitational RG flows on foliated spacetimes

The role of time and a possible foliation structure of spacetime are longstanding questions which lately received a lot of renewed attention from the quantum gravity community. In this talk, I will review recent progress in formulating a Wetterich-type functional renormalization group equation on foliated spacetimes and outline its potential applications. In particular, I will discuss first results concerning the RG flow of Horava-Lifshitz gravity, highlighting a possible mechanism for a dynamical Lorentz-symmetry restoration at low energies.

Guest Speakers: Ground transportation arrangements will be made on your behalf and instructions sent prior to your arrival. If you need transportation while attending the conference, we offer suggestions below. If flying, we suggest that you book your flight to arrive at Toronto International Airport (YYZ) or the Region of Waterloo International Airport (YKF).


Boulevard Limousine (estimated travel time 1hr) The fare for Boulevard Limousine for one passenger is $118.00 to the Toronto Airport.  The fare for one passenger from the Toronto Airport to Waterloo is $133.00.  To make reservations, please visit their website or call 519-886-8090.


Airways Transit (estimated travel time 1hr) Airways Transit connects Toronto (Pearson), Hamilton (Munro), and Region of Waterloo International Airports with the Kitchener-Waterloo area by providing 24 hour shared ride door-to-door service. To make reservations please visit their website or call 519-886-2121.


0001 Toronto Cabs (estimated travel time 1hr)  Approximately $90.00 rate for one-way: Toronto International Airport to Waterloo. Call 416-809-5656. Waterloo Taxi (estimated travel time 1hr)  Fixed $76.50 rate for one-way: Waterloo to Toronto International Airport. Call 519-886-1200.  Note: One or more passengers can split this $90.00 flat rate.


Car Rentals Upon arrival in any of the terminals at Pearson International Airport there are a number of car rental agencies to choose from. Their booths are located on the arrivals level. The cost of a car rental is dependent upon the type of vehicle you would like and the length of the stay. Driving Directions 

  • From the airport, follow signs for Highway 427 South/Highway 401.  
  • Continue to follow signs for Highway 401 West - London.  
  • Proceed West on Highway 401.  
  • Exit Highway 401 at Highway 8 West.  
  • Take exit 278 (Highway 8 West) and follow 8 West for 5 km to Highway 85, towards Highway 7 East. 
  • Proceed on Highway 85 for 5 km to Bridgeport Road exit. Turn right at the off-ramp, traveling west.  
  • Follow Bridgeport Road for 2 km into downtown Waterloo.  
  • Bridgeport is a four-lane one-way road. It becomes Caroline Street at Albert Street. Continue straight ahead.  
  • Travel forward another 200 metres, but ease over into the right-hand lane. As you go down a hill and around a curve, look for the green Perimeter Institute sign on the right hand side. The parking lot entrance is just after the sign (past the historic grist mill that sits on the edge of Silver Lake).  
  • Turn right into the PI parking lot entrance.

*Guest Speakers: Accommodation arrangements will be made on your behalf and instructions sent prior to your arrival. If you need accommodations while attending the conference, we offer suggestions for lodging below.


Waterloo Hotel 2 King Street North Waterloo, ON N2J 2W7 Phone: 519-885-2626 Distance from PI: 400 m


Waterloo Inn 475 King Street North Waterloo, ON N2J 2Z5 Reservation line: 1-800-361-4708 Reservation e-mail: reserve@waterlooinn.com Distance from PI: 3 km


Walper Terrace Hotel 1 King Street West Kitchener, ON N2G 1A1 Phone: 519-745-4321 Distance from PI: 4 km


Courtyard by Marriott 50 Benjamin Road East St. Jacobs, ON N2V 2J9 Phone: 519-884-9295 Distance from PI: 5.6 km

Scientific Organizers:

Bianca Dittrich, Perimeter Institute
Astrid Eichhorn, Perimeter Institute
Daniele Oriti, Albert Einstein Institute
Roberto Percacci, SISSA