Monday March 2 - Friday March 6 2009

organizers: Gert Aarts (Swansea University) & Shailesh Chandrasekharan (Duke University)

click here for the workshop schedule and pdf's of the talks

Fortunately, in recent years radical new approaches have been developed which can handle the sign problem or even eliminate it altogether. For a class of field and many-body theories, these methods are based on rewriting the partition function in a dual set of variables, similar to worldline (WL) representations. In many cases, the WL-approach suggests new solutions to the sign problem. Promising results have also been obtained using stochastic quantization and complex Langevin dynamics. In this case the sign problem is potentially circumvented by complexifying all degrees of freedom, so that the theory's phase space is explored in an inherently different fashion.

In this workshop we aim to learn about sign problems that arise in lattice field theory, understand what has been done and explore what can be done in the future. Although many of the researchers in the workshop will be interested in the physics of QCD at nonzero baryon density, we wish to bring researchers from nuclear and condensed matter physics to the workshop so that new ideas may emerge. We have in mind a rather technical, interdisciplinary workshop focusing on methods and techniques that have been used in different fields. Topics will concentrate on the following set of issues:

- Nature of sign problems
- Worldline formulations
- Complex Langevin methods
- Diagrammatic Monte Carlo
- Extrapolation methods
- Reweighting methods
- Other methods ...

- The organizers can be contacted at g.aarts @ swan.ac.uk (Aarts) and sch @ phy.duke.edu (Chandrasekharan).
- The number of participants is limited.
- Registration can be done at the
ECT* website, click on
**Meetings in 2009**to proceed to the registration link. - Registration is now closed
- The workshop will start Monday March 2 at 10am. Registration will open at 9am.
- The workshop will finish Friday March 6 at 5pm.
- There will be welcome buffet on Monday evening.
- click here for the workshop schedule

- Bartolome Alles
- Chris Allton
- Jacques Bloch
- Barak Bringoltz
- Philippe de Forcrand
- Massimo D'Elia
- Francesco Di Renzo
- Shinji Ejiri
- Gergely Endrodi
- Olga Goulko
- Sandor Katz
- Tamas Kovacs
- Dean Lee
- Maria-Paola Lombardo
- Joyce Myers
- Atsushi Nakamura
- Owe Philipsen
- David Reeb
- Erhard Seiler
- Denes Sexty
- Kim Splittorff
- Ion Stamatescu
- Boris Svistunov
- Urs Wenger
- Gert Aarts
- Shailesh Chandrasekharan

- Gert Aarts: Finite chemical potential with complex Langevin
- Bartolome Alles: The mass gap of the 2D O(3) Heisenberg model at theta=pi from simulations at imaginary theta
- Jacques Bloch: Random matrix theory as playground for the sign problem
- Barak Bringoltz: Baryon chemical potential in large N QCD
- Shailesh Chandrasekharan: Solution to sign problems in the worldline approach
- Philippe de Forcrand: Finite temperature and density QCD in the strong coupling limit
- Massimo D'Elia: Issues in analytic continuation: Spectral properties and the critical line
- Francesco Di Renzo: Langevin equation and complex actions: Are we missing anything? (discussion)
- Shinji Ejiri: A method to avoid the sign problem in finite density lattice QCD
- Gergely Endrodi: The curvature of the QCD phase transition line
- Dean Lee: Symmetries, signs, and complex actions in lattice effective field theory
- Maria-Paola Lombardo: Imaginary chemical potential and Taylor expansion: Mix & match
- Atsushi Nakamura: Searching paths to understand systems with a complex action
- Owe Philipsen: Lattice QCD at finite chemical potential (discussion)
- David Reeb: The severity of the sign problem in different regions of the dense-QCD phase diagram
- Erhard Seiler: Complex Langevin: Mathematical results and problems
- Denes Sexty: Real time simulations using stochastic quantisation
- Kim Splittorff: QCD with fixed complex fermion determinant
- Ion Stamatescu: What can we do with the complex action?
- Boris Svistunov: Diagrammatic Monte Carlo
- Urs Wenger: Solution of a sign problem by explicit bosonisation in two and three dimensions