Selected talks

• "Large groups in mathematics, small scales in physics and a reason for finding integer numbers"
  Opening talk of the Bielefeld school in theoretical sciencies BGTS
• "Some tools for equivariant constructions for 2-stacks and applications to conformal field theory"
  Talk given at Mathematics Department of the University of Lyon, February 2011

• "Gerbes on Lie groupoids"
  Talk given at the CRCG workshop Higher Structures in Topology and Geometry IV in Göttingen, June 2010.

• "Rational conformal field theory beyond semi-simplicity: challenges and puzzles"
  Talk given at the workshop Darstellungstheorietage in Jena, November 2009.

• "Mapping class group representations and conformal boundary conditions"
  Talk given at the workshop Lie algebras, vertex algebras and automorphic forms in Edinburgh, September 2009.

• "The fundamental gerbe on a compact Lie group"
  Talk given at the Seminar Sophus Lie in Göttingen, July 2009.

• "Higher gauge fields"
  Lectures at SFB 676 ``Particles, Strings and the Early Universe'', Hamburg April 17 and 24, 2009.

• "Mathematik als Kulturleistung"
  Vortrag und Folien für den Vortrag beim Hamburger Wissenschaftsforum

• "Bundle gerbes and surface holonomy."
  Talk given at the mathematics colloquium in Münster, October 2008.

• "Bundle gerbes: a geometric framework for Wess-Zumino terms."
  Talk given at the Schmidt-Fest in Heidelberg, September 2008.

• "Bundle gerbes and surface holonomy."
  Talk given at the European Congress of Mathematics (5ECM) in Amsterdam, July 2008.

• "Bibranes: Target space geometry for worldsheet defects."
  Talk given at the conference on the occasion of Jürg Fröhlich's 61st birthday in Zurich, July 2007.

• "Categorification and correlation functions in conformal field theory."
  Talk given at the International Congress of mathematicians (ICM) in Madrid, August 2006.

• "Twining characters and Picard groups in rational conformal field theories."
  Talk given at the conference "Lie algebras, vertex operator algebras and their applications" in Raleigh, a conference in honor of Robert L. Wilson and James Lepowsky, May 2005.

• "Picard groups in rational conformal field theory"
  Talk given at the conference "Non-commutative geometry and representation theory in mathematical physics" in Karlstad, July 2004.

• "Algebras in tensor categories and coset conformal field theories"
  Talk given at the 6th International Symposium Ahrenshoop on the Theory of Elementary Particles Ahrenshoop, August 2003.

• "Algebras in tensor categories and conformal field theory"
  Talk given at the AMS 2003 Spring Meeting, Bloomington IN, April 2003.

• "D-branes and broken bulk symmetries"
  Talk given at the Physics Department of Torino University. May 1999.

• "D-brane conformal field theory and traces on bundles of conformal blocks"
  Talk given at the Mathematics Department of UC Berkeley and at the workshop on Mathematical Aspects of String Theory (organizers D. Morrison and W. Nahm) at the Mathematisches Forschungsinstitut Oberwolfach, Germany. April 1999.

• "Twining characters and orbit Lie algebras"
  Talk at the workshop on Generalized Kac-Moody algebras (organizers P. Slodowy and R. Borcherds) at the Mathematisches Forschungsinstitut Oberwolfach, Germany. July 1998.

• "Kac-Moody algebras, WZW-models, and Verlinde formulae for (non-)simply connected groups"
  Talk at the workshop on conformal blocks and the Verlinde formula at the Mathematisches Forschungsinstitut Oberwolfach, Germany. March 1997.