### CFT, Gerbes and K-Theory in Oberwolfach, III

#### Posted by Urs Schreiber

This evening in Oberwolfach: Talks on open strings in WZW models and lots of private discussion.

After lunch today Konrad Waldorf gave an introduction to the WZW model, with some emphasis on the ‘modern’ description of the coupling in terms of an abelian gerbe with connection and curving. I will not reproduce any of the details because it should be standard material (and, I am tired), but I should mention that this gerbe stuff is discussed in

Krzysztof Gawedzki& Nuno Reis
**WZW branes and gerbes**

hep-th/0205233 .

After that introduction Christoph Schweigert began talking about more details concerning open strings on branes in WZW models and modules of gerbes. Unfortunaly I missed the very large part on modules because I was unexpectedly scheduled as the next speaker and had to fetch my notes.

But this material seems to be available in a ‘report’ about another Oberwolfach workshop last year. Have a look at Krzysztof Gawedzki’s notes **Gerbe-modules and WZW branes**
in this ps and check the references he gives there.

The very last talk today was mine, in which I tried to point out how a locally trivialized 2-holonomy functor gives rise to a cochain in nonabelian Deligne hypercohomology when differentiated and how this all fits into a nice diagrammatic picture.

I had a very interesting night-long private discussion about 2-bundles, gerbes, stacks and everything afterwards, but this has to sink in before I will talk about it here.

For tomorrow Dale Husemöller has announced a *digestible* review of Giraud’s original work on gerbes

J. Giraud

**Cohomologie non abélienne**

Springer-Verlag, Berlin (1971) .

After that Jarah Evslin and Hisham Sati will continue their ‘M-theory’ talks and in the afternoon Mathai and Bunke are scheduled to talk.

See you then, good night.