# Workshop on Strongly-Interacting Field Theories

**November 23 - 25**

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 lattice gauge theory, supersymmetric field theories, fermionic systems, and non-equilibrium dynamics.

Speakers include:

- Fakher Assaad, Würzburg
- Georg Bergner, Jena
- Jens Braun, Darmstadt
- Shailesh Chandrasekharan, Duke
- Masanori Hanada, Kyoto, Stanford
- Simon Hands, Swansea
- Anna Hasenfratz, Boulder
- Igor Herbut, Burnaby
- Lukas Janssen, Dresden
- Gernot Münster, Münster
- Ayan Mukhopadhyay, Wien
- Claudio Pica, Odense
- David Schaich, Bern
- Lorenz von Smekal, Giessen
- Björn Wellegehausen, Giessen

## Program

Program as PDF## Talks

#### Fakher Assaad

Competing orders in Dirac fermions#### Georg Bergner

Lattice simulations and extensions of the standard model with strong interactions#### Jens Braun

#### Falk Bruckmann

Dualizing lattice field theories at nonzero chemical potential#### Shailesh Chandrasekharan

Fermionic quantum criticality: Some recent results from large lattices- We discuss some recent results from lattice fermion models obtained from the perspective of the fermion bag approach, which allows us to perform Monte Carlo calculations on large lattices. We first discuss how fermion mass generation may be understood as a consequence of fluctuations of defects in space-time. We argue that this view point unifies various known mechanisms of mass generation in non-Abelian gauge theories and four-fermion models, including the one where fermion masses arise without spontaneous symmetry breaking. We then discuss some new Monte Carlo results from large lattices in a 2+1 dimensional Hamiltonian lattice model with minimal fermion doubling. We show deviations from earlier Monte Carlo results obtained with small lattices.

#### Masanori Hanada

#### Simon Hands

The 2+1d Thirring Model with U(2N)-invariant fermions- In 2+1 dimensions the global U(2N) symmetry associated with massless fermions is broken to U(N)⊗U(N) by a parity-invariant mass. I will show how to adapt the domain wall formulation to recover the U(2N)-invariant limit in interacting fermion models as the domain wall operation is increased. In particular, I will focus on the issue of potential dynamical mass generation in the Thirring model, postulated to take place for N less than some critical Nc. I will present simulations of the model using both HMC (N=2) and RHMC (N=1) algorithms, and also in the quenched limit N=0, and show that the outcome is very different from previous numerical studies of the model made with staggered fermions, where the corresponding pattern of symmetry breaking is distinct. The results support 0

#### Martin Hasenbusch

Fighting topological freezing in the two-dimensional CP^{N-1}model

- We perform Monte Carlo simulations of the CPN−1 model on the square lattice for N=10, 21, and 41. Our focus is on the severe slowing down related to instantons. To fight this problem we employ open boundary conditions as proposed by Lüscher and Schaefer for lattice QCD. Furthermore we test the efficiency of parallel tempering in a line defect. Our results for open boundary conditions are consistent with the expectation that topological freezing is avoided, while autocorrelation times are still large. The results obtained with parallel tempering are encouraging.

#### Anna Hasenfratz

Violation of Fermion Universality at a Conformal Fixed Point- The concept of universality is the basis for lattice investigations of quantum field theories. It is well understood at the perturbative fixed point that governs QCD-like systems but might not hold for some lattice fermions at the infrared fixed point of conformal systems. In a recent work we addressed the issue by calculating the renormalized beta function using domain wall fermions with Symanzik gauge action and fully O(a
^{2})-improved Zeuthen gradient flow. We find a qualitatively and quantitatively different renormalized beta function compared to results obtained with staggered fermions. This leads to the conclusion that the two fermion formulations are not in the same universality class which strongly impacts lattice field theory studies of conformal or near-conformal systems using staggered fermions.

#### Igor Herbut

Fixed point collisions and tensorial order parameters in some relativistic and non-relativistic field theories#### Lukas Janssen

A fermionic gauge theory for bosonic deconfined criticality- I will discuss the QED3-Gross-Neveu model which describes massless Dirac fermions coupled to a critical scalar field and a U(1) gauge field in 2+1 dimensions. This theory has recently been suggested to be dual to the SU(2) noncompact CP1 model - the purely bosonic field theory for the deconfined phase transition between the Néel antiferromagnet and the valence bond solid on the square lattice. I will present the critical behavior of the QED3-Gross-Neveu model, elucidate the relation to previous results for the purely fermionic Gross-Neveu model as well as QED3, and compare with predictions from the conjectured boson-fermion duality.

#### Gernot Münster

A glimpse of supersymmetric Yang-Mills theory and technicolor models on a lattice- Models for physics beyond the Standard Model include supersymmetry and technicolor. This talk gives an introduction to basic features of supersymmetric Yang-Mills theory and technicolor models and non-perturbative investigations of them on a lattice.

#### Ayan Mukhopadhyay

A hybrid model for thermalization- In systems like the Quark-Gluon Plasma produced by heavy-ion collisions, it is necessary to include both weakly and strongly coupled degrees of freedom at various energy scales to understand its time-evolution and thermalization. I will present a non-perturbative effective approach called semi-holography which combines perturbative methods for weakly coupled partons with the holographic duality for the strongly coupled infrared to develop a consistent framework in a wide range of energy scales. I will describe some progress in deriving such a framework from first principles. I will also describe a phenomenological construction aimed towards a better understanding of the QGP and present our recent results on the collective flow near thermal equilibrium. Our results relate remarkably diverse behavior across a wide range of energy scales.

#### Claudio Pica

Lattice models of Composite Higgs dynamics#### David Schaich

Lattice studies of maximally supersymmetric Yang-Mills theories#### Lorenz von Smekal

#### Björn Wellegehausen

## Posters

#### Lennart Dabelow

#### Bernhard Ihrig

#### Benjamin Knorr

#### Ricardo Martini

A curvature bound from gravitational catalysis#### Emilio Torres

#### Bitan Roy

Quantum critical behavior of relativistic spin-3/2 fermions in (2+1)-dimensions#### Marc Steinhauser

#### Daniel August

#### Juan Camilo Lopez

#### Roman Höllwieser

## List of Participants

- Amadeo Jimenez Alba, Jena
- Martin Ammon, Jena
- Fakher Assaad, Würzburg
- Daniel August, Jena
- Oliver Bär, Berlin
- Alexei Bazavov, Michigan
- Georg Bergner, Jena
- Jens Braun, Darmstadt
- Falk Bruckmann, Regensburg
- Shailesh Chandrasekharan, Duke U.
- Lennart Dabelow, Bielefeld
- Sebastián Franchino-Viñas, Jena
- Holger Gies, Jena
- Masanori Hanada, Kyoto, Stanford
- Simon Hands, Swansea
- Martin Hasenbusch, Berlin
- Anna Hasenfratz, Boulder
- Igor Herbut, Simon Fraser U.
- Roman Höllwieser, Wuppertal
- Berhard Ihrig, Heidelberg
- Lukas Janssen, Dresden
- István Kaposvári, Jena
- Felix Karbstein, Jena
- Benjamin Knorr, Nijmegen
- Julian Johannes Lenz, Jena
- Juan Camilo Lopez, Jena
- Ricardo Martini, Jena
- Ayan Mukhopadhyay, Wien
- Gernot Münster, Münster
- Claudio Pica, Odense
- Bitan Roy, Dresden
- David Schaich, Bern
- Michael Scherer, Köln
- René Sondenheimer, Jena
- Marc Steinhauser, Jena
- Andre Sternbeck, Jena
- Emilio Torres, Köln
- Alessandro Ugolotti, Jena
- Lorenz von Smekal, Giessen
- Björn Wellegehausen, Giessen
- Andreas Wipf, Jena
- Ulli Wolff, Berlin
- Luca Zambelli, 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)