Asymptotic Safety - 30 Years Later

Conference Date: 
Thursday, November 5, 2009 (All day) to Sunday, November 8, 2009 (All day)


One of the  salient challenges in modern theoretical physics is the construction of a quantum theory of gravity. This challenge has been addressed over time from many original, and sometimes exotic, points of view. A very conservative solution, going under the name of "asymptotic safety," exists somewhat surprisingly within the realm of usual quantum field theory and the renormalization group. Proposed 30 years ago, it has recently received strong support thanks to new techniques in non-perturbative quantum field theory.


This workshop will bring together researchers who are currently working on asymptotic safety (or worked on it in the past) and researchers who are working on alternative ideas which can bring a new light on the subject. The aim of this meeting is to combine these alternative points of view and reach a better understanding of the results obtained so far, of their interpretation and relevance for quantum gravity.



Confirmed Invited Speakers To Date:

Jan Ambjorn, Utrecht University

Alfio Bonanno, INAF, Catania

Daniel Litim, University of Sussex

Holger Gies, ITP, Jena University

Renate Loll, Utrecht University

Max Niedermaier, Tours University

Martin Reuter, Mainz University

Vincent Rivasseau, University Paris-Sud XI

Frank Saueressig, Mainz University

Lee Smolin, Perimeter Institute

Arkady Tseytlin, Imperial College, London

B.F.L. Ward, Baylor University 

Steven Weinberg, University of Texas, Austin

Jean Zinn-Justin, CEA, Saclay


Other Participants Attending:

Petr Horava

Michael Scherer

Astrid Eichhorn

Adriano Contillo

Omar Zanusso

Gaurav Narain

Cliff Burgess

Sean Gryb

Stefan Floerchinger

Gian Paolo Vacca

Christoph Stephan

Giovanni Venturi


Jan Ambjorn, Utrecht University

CDT and asymptotic safety

CDT is a lattice regularization of quantum gravity. The phase structure of the lattice theory is discussed and a candidate UV fixed point located.

Alfio Bonanno, INAF, Catania

The mass-inflation phenomenon in the asymptotic safety scenario

John Joseph M. Carrasco, UCLA

Perturbative cancellations in gravity theories

I will present recent results through four loops demonstrating that the maximally supersymmetric (N=8) generalization of gravity is surprisingly well behaved in the ultraviolet as a result of unexpected cancellations between contributing terms.  These cancellations first manifest at one loop in the form of the "no-triangle property," with all-loop order implications through unitarity.  I will conclude by discussing similar novel cancelations identified in pure Einstein gravity, at one loop, which suggest a possible explanation for the unexpectedly tame high energy behavior of N=8 supergravity beyond the limited UV protection of supersymmetry.

Holger Gies, ITP, Jena University

Mechanisms of Asymptotic Safety

Renate Loll, Utrecht University

Nonperturbative Insights from Causal Dynamical Triangulations

Max Niedermaier, Tours University

Gravitational fixed points and asymptotic safety from perturbation theory

Christoph Rahmede, Jena University

Renormalization Group Flow in Scalar-Tensor Theories

Martin Reuter, Mainz University

Gravitational average action and asymptotic safety: past and future

Vincent Rivasseau, Université Paris-Sud XI, Orsay

A New Mechanism for Asymptotic Safeness

Frank Saueressig, Mainz University

Exploring the Theory Space of Asymptotically Safe Quantum Gravity

Michael Scherer, ITP, Jena University 

A mechanism for Asymptotic Safety of chiral Yukawa systems

We will discuss Weinberg's idea of asymptotic safety for a chiral Yukawa system with a U(N_L)_L x U(1)_R symmetry in a leading-order derivative expansion using nonperturbative functional RG equations. As a toy model sharing important features with the standard model we explicitely discuss N_L=10 for which we find a non-Gaussian fixed point and compute its critical exponents. We observe a reduced hierarchy problem and obtain predictions for the toy Higgs and the toy top mass.

Lee Smolin, Perimeter Institute

Asymptotic safety and deformed symmetry 

I review work on asymptotic safety in quantum gravity in a 1/N expansion.  I highlight the result that the scaling behavior governed by the non-trivial fixed point must be characterized by a scaling dimension less than four.  Otherwise a Weyl curvature squared counterterm is required, that renders the theory unstable. This reduced scaling dimension then implies that Lorentz invariance is either broken or deformed, and this is transmitted to the matter sector. However, there are strong constraints on breaking of Lorentz invariance at the Planck scale due to the absence of birefringence of photons. The present constraints on deforming Lorentz invariance are, however, just at the Planck scale.  I will then review semiclassical quantum gravity arguments that Lorentz symmetry is deformed.

Arkady Tseytlin, Imperial College, London

Comments on UV divergences in quantum gravity

Gian Paolo Vacca, Bologna University

Quantum Gravitational Corrections to Matter: A Running Controversy   

B.F.L. Ward, Baylor University

Asymptotic Safety and Resummed Quantum Gravity

In Weinberg’s asymptotic safety approach to quantum gravity, one has a finite dimensional critical surface for a UV stable fixed point to generate a theory of quantum gravity with a finite number of physical parameters. The task is to demonstrate how this fixed point behavior actually arises. We argue that, in a recently formulated extension of Feynman’s original formulation of the theory, which we have called resummed quantum gravity, we recover this fixed-point UV behavior from an exact re-arrangement of the respective perturbative series. We argue that the results we obtain are consistent both with the exact field space Wilsonian renormalization group results of Reuter and Bonanno and with recent Hopf-algebraic Dyson-Schwinger renormalization theory results of Kreimer. We calculate the first "first principles" predictions of the respective dimensionless gravitational and cosmological constants and argue that they support the Planck scale cosmology advocated by Bonanno and Reuter as well. Comments on the prospects for actually predicting the currently observed value of the cosmological constant are also given.

Steven Weinberg, University of Texas, Austin

Prospects for Asymptotic Safety

Omar Zanusso, SISSA

Asymptotic safety in the nonlinear sigma models and gravity

Jean Zinn-Justin, CEA, Saclay

Asymptotic safety: a review

I shall review on field theory examples, the meaning of the concept of asymptotic safety in the context of low energy effective field theories.