Tuesday, April 12, 2005


I have been silent for much too long. So in this post I will mention a few things that kept me busy (for the impationed reader, these are a course on string theory that I co-teach, a short paper on non-commutative SU(N) theories, presenting this paper at two workshops and jigsaw puzzles).

Most of my time currently is taken by teaching string theory to advanced undergrads and new grad students. This is the first proper course that I teach and I find this even more entertaining than anticipated. The first half of the course was based on Zwiebach's book, but I took some shortcuts (not discussing so much of the classical theory, I used Polyakov's rather than the Nambu-Goto action and went to conformal gauge immediately, finally I treated closed strings first and only then discussed boundary conditions). For the second half, I am aiming more at the modern stuff: I hope I will cover some M-Theory (more or less the content of the classic string theory dynamics in various dimensions and show how to compute the v^4/r^7 in M(atrix) theory.

So far, I am particulary proud of two lectures I did: The first started with formal boundary conditions and in the end I had convinced everybody that D-branes are dynamical objects all by mainly drawing comic pictures of D-branes and strings. The other one was a one hour introduction to spinors and Clifford algebras in all dimensions. Today, I will hand out a problem set that asks the students to show that 10D SYM is supersymmetric (based on the appendix of chapter 4 in GSW.
Hmm, do my students read this???).

Given they only knew quantum mechanics at the beginning of the term, I think (hope) they have learnt a lot.

The other thing is, that my position here at IUB is paid by a project from the DFG, the German science foundation that is part of the string theory progam they run and is supposed to be about applications of non-commuative geometry.

Thus I got back into these matters and recently at the "Beyond the standart model" workshop I wanted to talk about something else then the Loop String (I will do this again in two weeks time in Hannover) so I put out a proposal how to properly define the free, decoupled center of mass U(1) for a D-brane with constant B-field which induces non-commutativity.

Next Monday, I will present this as well at the DFG string Schwerpunkt (center of mass, sic) workshop. However, I cannot talk 45 minutes about a five page paper, so will have to come up with something else. Most likely (still six days to go) it will be more about non-commutative and non-abelian D-branes (my title is Non-commutative vs non-abelian) and I will also cover some of Peter's ideas. This is supposed to be also about future plans but I don't feel too comfortable to talk about things that haven't been demonstrated to work, yet.

Finally, I also had my birthday recently. Among the things I got was a jigsaw puzzle (my dad proved questionable test when he picked that picture. The motivation appears to be that A. and I quite liked the Hopper exhibition at Tate Modern last summer). The other thing I got is a digital camera, so now, you, dear readers of my blog, can watch my progress with the puzzle.

On day one I did some basic sorting and assembled part of the boundary and the jelly bears:

On day two, I finished the boundary and made some progress on the bulk:

I wonder if everybody has this holographic approach to do puzzles? Furthermore, it's really like string theory: You work out some local bit (e.g. a pink jelly bear) and then this medium size structure just fits with what you have done before on a global scale. Amazing.


Anonymous said...

You teach string theory to undergrads? Wow!

Robert said...

Well, it's more like "an easy route to selected topics in string theory". But we honestly did for exampe the canocical quantization of the bosonic string in light cone gauge and found the critical dimension.

The trick is to make everything look like quantum mechanics rather than QFT.

For susy, we really only did susy QM and then I claimed that "like the unpaired ground state in SQM there are special (BPS) states with less degeneracy whose existence is stable under continious transformations of the theory".

The stuff with spinors and Fierz identities was besides it's good to know in its own right only needed to derive the massless fields in type II theory.