Tuesday, April 19, 2005

DFG Schwerpunkt

Despite having a bad cold, yesterday, I attended the DFG Schwerpunk stringtheory workshop at DESY. I was quite surprised that half of the speakers (well, including myself) talked about non-commutative geometry of one sort or the other. Does this mean that this subject is not completely dead in 2005 or does it just mean physicists in Germany have not noticed, yet?

However, the talk that caught my attention was by Michael Ratz from Bonn. He described some ideas to use finite temerature field theory in conjunction with moduli stabilization.

According to his talk, whatever you do (KKLT or race-track or, you name it), the typical moduli potential if it has a minimum at some finite value at all, it is an exponentially decreasing function with some bump in it such that the local minimum is separated form the minimum at infinity by a potential wall of height typically proportional to the gravitino mass (the susy breaking scale) squared.

But if you now crank up the temperature, the thermal effective potential tends to wash out the bump like it washes out the bump in the Mexican hat potential in the electro-weak phase transition. So above some critical temperature (roughly the geometric mean of the susy breaking and the Planck scale) there is no local mimimum anymore and the moduli run off to infinity.

Thus when you design your universe you should make sure that the reheating after inflation does not reach that critical temerature as otherwise you wouldn't have finite couplings and compact dimensions of finite size anymore later.

This bound is not very tight but Michael claims it is quite model independant. I must say I like the idea of having temperature and thus time (at cosmological scales) dependant moduli fields...

Friday, April 15, 2005

Musical Friday

It's Friday, and me too, I would like to say a few words about music. In retrospect, I am surprised not to have mentioned it so far given the importance is has to me. These days, not only Queen will have a reunion but my Jazz band in Hamburg as well and I am seriously practising my alto sax again.

But let me also first do a random ten (I set xmms to random mode and will comment the ten songs that come up. I'll try to be honest and not skip boring ones):

1. Mona Lisa played by Keith Jarret's trio. Jarret is my absolute piano hero. The Bregenz solo concert is what got me into serios jazz a long time ago (after some initial Boogie Woogie infection probably caused by Bernd Röser, my infinitely patient piano teacher). As a kid I hardly ever practised, so my classical skills are still rudimentary but out of pure desperation he taught me all the theory including advanced harmony that comes so handy for playing jazz later. And in the long term I benefit so much more from this than if I had learned to play more Beethoven sonatas. And I still do a Booggie Woogie every now and then as this is pure fun.

2. Eine schöne Party by Götz Alsmann. Alsmann is to my mind the only true living alround entertainer. He can be a talkshow host (Zimmer frei being slightly surreal), can sing and play piano on stage. Amazing. And he is about fourtyfive, holds a PhD in musicology and as I hear is one of the world best ukulele players.

3. Elephant Hips by Rabih Abou Khalil. This guy does a great mixture of modern jazz and oriental music. A must hear. Sometimes reminds me of John Zorn's Masada project.

4. For All We Know by Dave Brubeck. This comes from the "Great Concerts" live album, also one of my first CDs. Thinking of it, it's probably my dad's. Besides Take Five they also do wonderful versions of other songs: A feverish Take the A Train, Pennies From Heaven is the opening song and Three To Get Ready is probably my favourite Brubeck tune (we also to to this 3/4 3/4 4/4 4/4 tune with our band).

5. Three Strikes and You're Out by The Foremen. This is from a political comedy CD I bought during Clinton's second presidential campain when I was a summer student in Princeton. These guys were interviewed on public radio while I had my breakfast and I do not regret buying the CD afterwards.

6. Take Me There by Grover Washington Jr. Admitedly, this is elevator music. I bought the CD because of Modaji, which is one of my fusion favourites (and it is featured on the play along CD of the New (legal) Real Book).

7. Your Congratulations by Alanis Morissette. I still claim I discovered Alanis Morissette before the hype. I mentioned above my summer in Princeton. In late September, I took a week off, rented a car and went to New England to see Indian Summer. Somewhere in New Hampshire there was this song on the radio with the chorus "...and I've got one and in my pocket and the other one..." which I thought was quite cool. I stopped in the next town which turned out to be some hippie colony and went to the record store. The 150kg guy behind the counter did not recognise my singing but sang it again much louder (really, like in the Leasureship Larry In The Land Of Lounge Lizards computer game where you have to ask for condoms in the pharmacy). And indeed, some teenager browsing the CDs knew that this was Alanis Morisette and I bought the tape for the car.

8. Hit Me by Defunkt. Wonderful energy, this can really wake you up. I have seen them live a couple of times and all those were amazing gigs. Even with a trombone player as front man.

9. Ariana by Spyro Gyra. I don't know why but this is my only CD of this very influential jazz rock band. Don't have much to say about it.

10. Celebration After Billies Capture by Bill Frisell. I love this man, besides Mike Stern (who is very different in style) my favourite guitar player. The first group I heard him with was a concert on TV with John Zorn's Naked City (if you don't know this you must get hold of the CD!!!) and after that he has played an amazing variety of different styles (all at the highest level): He performed live to Buster Keaton silent movies, did this CD (with tunes ranging from Madonna over Souza marches to Aaron Copeland) did the music for "Million Dollar Hotel" and toured with the Intercontinentals (I attended the gig at Cambridge's Corn Exchange).

This was much more fun than expected. I am surprised that none of the many Michael Brecker songs on my playlist came up. And will have to blog about Beatles some other time and just mention a real expert

Wednesday, April 13, 2005


In Germany, hardly anybody uses their mid-initials, many people don't even have one. So, it was just to distance myself from the crowd that I started using the C. about ten years ago (guess what it stands for).

However, in the global village, the mid-initial can be useful to tell people apart. No, I am not talking about W., but for example, there is Robert B. Helling, a professor of microbiology at UMich. In Cambridge University, there are two Michael Greens and email addresses typically use all initials. I am rch47.

And today I got an email from amazon.com stating
We've noticed that customers who have purchased "The Elegant Universe:
Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory" by
Brian Greene also purchased books by Sean B. Carroll. For this reason, you
might like to know that Sean B. Carroll's "Endless Forms Most Beautiful:
The New Science of Evo Devo and the Making of the Animal Kingdom" is now
available .

So, Sean Caroll, owner of the Preposterous Universe is not only blogging anti-Intelligent Design but after his GR book has written a book on evolution? Well, this is SBC.

PS: No, I don't use the Elegant Universe for my string course or my research. I bought it for a friend how kept bugging me what this theory is about that I am working on.

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.