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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 Loll, Radboud 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 Rivasseau, Université Paris-Sud XI Orsay
James Ryan, Albert Einstein Institute
Dine Ousmane Samary, Perimeter Institute
Frank Saueressig, Radboud 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, University of Waterloo
- 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 Waterloo
- 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 Haggard, Centre 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
- Aldo Riello, CPT Luminy, Aix-Marseille Universit
- 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 |
Bob Room |
10:10 – 11:10am |
Overview Causal Dynamical Triangulations Renate Loll, Radboud University Nijmegen |
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 |
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 |
Bob Room |
3:20 – 4:20pm |
Overview Renormalization in Spin Foams Bianca Dittrich, Perimeter Institute |
Bob Room |
4:20 – 4:50pm |
Break |
Bistro – 1st Floor |
4:50 – 6:00pm |
Challenge Talks Lee Smolin, Perimeter Institute & |
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 Daniel Litim, University of Sussex |
Bob Room
|
10:20 – 11:00am |
Break |
Bistro – 1st Floor |
11:00 – 11:40am 11:40 – 12:20pm |
Connecting the RG in gravity to phenomenology cont. Alfio Bonanno, INAF Kellogg Stelle, Imperial College, London |
Bob Room |
12:20 – 1:00pm |
Discussion of morning talks (How) can we extract phenomenological consequences of the RG flow in gravity? |
Bob Room |
1:00 – 2:00pm |
Lunch |
Bistro – 2nd Floor |
2:00 - 3:30pm |
Perimeter Institute Colloquium |
Theater |
3:30 – 4:10pm 4:10 – 4:50pm |
Connections between methods and results from different approaches Tim Koslowski, University of New Brunswick Jan Ambjorn, Niels Bohr Institute |
Bob Room |
4:50 - 5:10pm | Break | Bistro – 1st Floor |
5:10 – 5:50pm |
Connections between methods and results from different approaches cont. Mercedes Martin-Benito, Radboud University Nijmegen |
Bob Room |
5:50 – 6:40pm |
Discussion Is there a relation between some approaches? |
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 Jan Pawlowski, University of Heidelberg |
Bob Room |
10:20 – 11:00am |
Break |
Bistro – 1st Floor |
11:00 – 11:40am |
Renormalization Group in gravity and symmetries cont. Benjamin Bahr, University of Hamburg |
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 |
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 Dario Beneditti, Albert Einstein Institute |
Bob Room
|
3:50 – 4:30pm |
Break |
Bistro – 1st Floor |
4:30 – 5:10pm |
Lorentz invariance and the RG flow in gravity cont. Frank Saueressig, Radboud University Nijmegen |
Bob Room |
5:10 – 6:00pm |
Discussion What are the mechanisms for restoration of symmetry during |
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 Astrid Eichhorn, Perimeter Institute |
Bob Room |
10:20 – 11:00am |
Break |
Bistro – 1st Floor |
11:00 – 11:40am |
What are the fundamental gravitational degrees of freedom?cont. Joshua Cooperman, Radboud University Nijmegen |
Bob Room |
11:40 – 12:20pm |
Discussion What are the degrees of freedom we should use in a gravitational path integral? |
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 Vincent Rivasseau, Université Paris-Sud XI Orsay |
Bob Room |
3:50 – 4:30pm |
Break |
Bistro – 1st Floor |
4:30 – 5:10pm |
Renormalization Group in spacetime vs. group space cont. James Ryan, Albert Einstein Institute |
Bob Room |
5:10 – 6:00pm |
Discussion What is the meaning of asymptotic freedom or asymptotic |
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
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.
Zheng-Cheng Gu, Perimeter Institute
Grassmann tensor network renormalization and fermionic topological quantum field theory: a new route towards quantum gravity
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?
Daniel Litim, University of Sussex
Lessons from asymptotic safety
Two aspects of asymptotic safety are highlighted. First, I discuss how asymptotic safety can be tested with the help of a bootstrap strategy. This is then applied to high-order polynomial actions of the Ricci scalar and beyond. Second, I discuss how phenomenological signatures of asymptotic safety can be searched for at particle colliders such as the LHC, provided that the quantum gravity scale is in the TeV energy regime.
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
Between Matrices and Tensors
Quartic tensor models can be rewritten in terms of intermediate matrix fields. The corresponding expansion is not only simpler, it suggests also new bridges between matrices, strings and tensors.
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.
Kellogg Stelle, Imperial College, London
What happens to the Schrödinger solution in quantum corrected gravity?
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.
Grassmann tensor network renormalization and fermionic topological quantum field theory: a new route towards quantum gravity
Recently, the development of tensor network renormalization approach has provided us a powerful tool to construct new classes of topological quantum field theories(TQFTs) in discrete space-time. For example, the Turaev Viro’s states sum constructions are fixed point tensor networks representing a special class of 2+1D TQFTs. Interestingly, the Grassmann variable generalization of tensor network renormalization approach leads to new classes of TQFTs for interacting fermion systems, namely, the fermionic TQFTs.
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.
Asymptotic safety in a pure matrix model
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.
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?
What happens to the Schwarzschild solution in quantum corrected gravity?
Confronting Asymptotically Safe Inflation with Planck data
Lessons from asymptotic safety
Two aspects of asymptotic safety are highlighted. First, I discuss how asymptotic safety can be tested with the help of a bootstrap strategy. This is then applied to high-order polynomial actions of the Ricci scalar and beyond. Second, I discuss how phenomenological signatures of asymptotic safety can be searched for at particle colliders such as the LHC, provided that the quantum gravity scale is in the TeV energy regime.
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.
What are the most pressing open questions in the application of the RG to gravity?
Pages
Scientific Organizers:
Bianca Dittrich, Perimeter Institute
Astrid Eichhorn, Perimeter Institute
Daniele Oriti, Albert Einstein Institute
Roberto Percacci, SISSA