# Workshop on Strongly-Interacting Field Theories

**November 5 - 7**

This workshop is founded by the DFG research training unit "Quantum and Gravitational Fields" (GK1523/2) and aims to bring together researchers from different areas of theoretical physics who study properties of strongly-interacting field theories. The main goal of the workshop is to provide a platform of the communication between people working on different aspects of strongly-interacting field theories, in order to allow for a transfer of knowledge and methods.

This year's workshop puts a special emphasis on quantum field theory approaches to quantum

gravity.

Speakers include:

- Dario Benedetti, Paris
- N. Emil Bjerrum-Bohr, Copenhagen
- Alessandro Codello, Odense
- Giulio D'Odorico, Nijmegen
- Astrid Eichhorn, London
- Stefan Fredenhagen, Potsdam
- Andrzej Görlich, Copenhagen
- Razvan Gurau, Palaiseau
- Herbert Hamber, Irvine
- Stefan Hollands, Leipzig
- Daniel Litim, Sussex
- Daniele Oriti, Potsdam
- Jan Pawlowski, Heidelberg
- Roberto Percacci, Trieste
- Hanno Sahlmann, Erlangen
- Gian Paolo Vacca, Bologna

## Program

Program as PDF

## Talks

#### Dario Benedetti

Renormalization Group Flows in Tensorial Group Field Theories#### N. Emil Bjerrum-Bohr

Unitarity and Effective Field Theory Results in Quantum Gravity#### Alessandro Codello

Covariant Effective Field Theory of Gravity- Using covariant methods we construct the effective field theory of gravity as a loop expansion in inverse powers of the Planck mass, distinguishing classical, leading and next-to-leading quantum corrections. We then compute the leading corrections in a curvature expansion to quadratic order. We specialize the effective action to FRW spacetimes and we derive the related effective Friedmann equations. We show that for particular values of the parameters we recover many different non-local modifications of general relativity recently proposed that are able to describe both early and late time cosmology.

#### Giulio D'Odorico

Horava-Lifshitz gravity from a functional renormalization group perspective- Over the last years there has been an increasing awareness that renormalization group methods may play a decisive role for establishing a consistent theory of quantum gravity within the realm of quantum field theory. In this talk I will discuss novel results on the heat-kernel expansion of differential operators obeying the anisotropic dispersion relations typical for Horava-Lifshitz gravity. Based on these results quantum effects in Horava-Lifshitz gravity can be computed in a covariant way. In particular they allow the identification of the anisotropic Gaussian fixed point underlying the renormalizability of the theory. The relation between this anisotropic fixed point and the non-Gaussian fixed point appearing in the Asymptotic Safety program will be discussed.

#### Astrid Eichhorn

Does asymptotically safe quantum gravity have to be a TOE?- Here, I will argue that a viable description of quantum spacetime in our universe must account for the observed matter fields and their properties. In the context of asymptotically safe quantum gravity I will argue that this most likely requires the existence of an interacting Renormalization Group fixed point for gravitational and matter degrees of freedom. I will review what we already know about the properties of such a fixed point, and will highlight some potential phenomenological consequences as well as some open questions.

#### Stefan Fredenhagen

On higher-spin gravity in three dimensions#### Andrzej Görlich

Phase Diagram of Simplicial Quantum Gravity#### Razvan Gurau

(More on) Phase Transitions in Tensor Models#### Herbert Hamber

Regge-Wheeler Lattice Formulation for Gravity- I will review a number of key aspects related to the lattice formulation of gravity, both in the Euclidean path integral approach and in the context of the (Hamiltonian) lattice Wheeler-DeWitt equation. First I will describe in some detail the lattice weak field expansion, a necessary ingredient for connecting the theory to the continuum, and then the setup required to compute diffeomorphisms invariant averages and correlations non-perturbatively from the discretized Feynman path integral. In this context the renormalization group approach is understood to play a key role in constructing the correct quantum lattice continuum limit. Some analogies with Wilson’s lattice gauge theory formulation for QCD will be discussed as well.

#### Stefan Hollands

Operator product expansion- The operator product expansion (OPE) is a well-known tool in quantum field theory and statistical mechanics. It not only has many practical uses, but is also important conceptually, because it can be seen as describing the algebraic backbone of the theory — a viewpoint that is particularly transparent in CFTs. Nevertheless, there are still many open questions surrounding this expansion, in particular outside the realm of CFTs. Here I want to present novel results about 1) sharp bounds on the remainder in an OPE of correlation functions, which in particular show that the convergence of the OPE is much better than previously expected 2) A novel recursive scheme for constructing the OPE coefficients to arbitrary orders in perturbation theory but which in principle is even completely well-defined at the non-perturbative level 3) a completely satisfactory clarification of the "associativity" or "crossing symmetry" property of the OPE including non-conformal QFTs.

#### Benjamin Knorr

Parametrisation dependence in non-perturbative approximations of quantum gravity#### Stefan Lippoldt

Gravity, Fermions and Spin Base Invariance#### Daniel Litim

Asymptotic safety and fixed points of quantum gravity#### Daniele Oriti

Group field theories for the atoms of space, and their renormalization#### Jan Pawlowski

Local quantum gravity & matter#### Roberto Percacci

On the choice of gauge and parametrization in quantum gravity#### Hanno Sahlmann

From groups and knots to black hole entropy - some aspects of loop quantum gravity- I will survey the formalism and main results of loop quantum gravity. Then I take a closer look at the way black hole horizons are treated in the theory, by coupling a Chern-Simons theory on the horizon to the bulk degrees of freedom. I will present some recent results on a way to solve the self-duality equation involved directly in the quantum theory.

#### Gian Paolo Vacca

Some results for a f(R) truncation for the QG action using the exponential parametrisation of the metric## Posters

#### Natália Alkofer

Spectral dimensions from the Spectral Action#### Reinhard Alkofer

Rotating Mass Shell: A counter-example to Mach's principle?#### Julia Borchardt

Global solutions of functional fixed point equations via pseudo-spectral methods#### Nicolai Christiansen

Local Quantum Gravity#### Tobias Denz

2-to-2 scattering of gravitons / flow of the graviton 4-point function#### Gulio D'Odorico

Quantum Phase Transitions in the BKL Universe#### Antônio Duarte

A non-perturbative BRST symmetry for the Gribov-Zwanziger action#### Kevin Falls

Gauge independence, convexity, and scaling exponents in quantum gravity#### Aaron Held

Modified Yukawa Interactions from Quantum Gravity#### Tobias Hellwig

SuSy FRG: An overview#### Peter Labus

#### Carlo Pagani

#### Manuel Reichert

Asymptotic safety of gravity-matter systems- We study the ultraviolet stability of gravity-matter systems for general numbers of minimally coupled scalars and fermions. It includes full dynamical propagators and a genuine dynamical Newton's coupling, which is extracted from the graviton three-point function. We find ultraviolet stability of general gravity-fermion systems. Gravity-scalar systems are also found to be ultraviolet stable within the reliability bounds of the current approximation scheme. Remarkably, the ultraviolet fixed points for the dynamical couplings are found to be significantly different from those of their associated background counterparts, once matter fields are included. In summary, within the limits of the given approximation the asymptotic safety scenario does not put constraints on the matter content of the theory.

#### Mahmoud Safari

Splitting Ward identity for functional background-field flows## List of Participants

- Natalia Alkofer, Nijmegen
- Reinhard Alkofer, Graz
- Martin Ammon, Jena
- Dario Benedetti, Paris
- Julia Borchardt, Jena
- N. Emil Bjerrum-Bohr, Copenhagen
- Nicolai Christiansen, Heidelberg
- Alessandro Codello, Odense
- Tobias Denz, Heidelberg
- Giulio D'Odorico, Nijmegen
- Antônio Duarte, Trieste
- Astrid Eichhorn, London
- Kevin Falls, Heidelberg
- Stefan Fredenhagen, Potsdam
- Holger Gies, Jena
- Andrzej Görlich, Copenhagen
- Razvan Gurau, Palaiseau
- Herbert Hamber, Irvine
- Aaron Held, London
- Tobias Hellwig, Jena
- Stefan Hollands, Leipzig
- Amadeo Jimenez-Alba, Jena
- Felix Karbstein, Jena
- Benjamin Knorr, Jena
- Peter Labus, Trieste
- Julian Leiber, Jena
- Stefan Lippoldt, Jena
- Daniel Litim, Sussex
- Andreas Nink, Mainz
- Nobuyoshi Ohta, Higashi-Osaka
- Daniele Oriti, Potsdam
- Carlo Pagani, Mainz
- Michel Pannier, Jena
- Jan Pawlowski, Heidelberg
- Roberto Percacci, Trieste
- Ludovic Planté, Saclay
- Karl-Henning Rehren, Göttingen
- Manuel Reichert, Heidelberg
- René Sondenheimer, Jena
- Mahmoud Safari, Tehran
- Hanno Sahlmann, Erlangen
- Vedran Skrinjar, Trieste
- Sebastian Ulbricht, Jena
- Gian Paolo Vacca, Bologna
- Björn Wellegehausen, Gießen
- Andreas Wipf, Jena
- Luca Zambelli, Jena
- Omar Zanusso, Jena

The workshop will be held at:

Haus "Zur Rosen"

Johannisstraße 13

07743 Jena

Größere Kartenansicht

Arrival by plane:

Airport Halle/Leipzig (+ 1h train ride, one-way ticket ~35 Euros )

Airport Berlin (Tegel or Schoenefeld) (+ 3h train ride, one-way ticket ~65 Euros)

Airport Frankfurt (+ 3h train ride, one-way ticket ~75 Euros)

Airport Munich (+4h train ride, one-way ticket ~85 Euros)

Arrival by train:

There are two train stations in Jena: Jena-Paradies (directions Berlin or Munich), and Jena-West (direction Frankfurt). The hotels as well as the conference site are in walking distance from both stations (taxi ride ~ 5-10 Euros)