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...


Anonymous said...

Hi Robert,

I am wondering if you are unhappy with the comments to your latest String Coffee Table entries or with the SCT environment so that you have decided to post all your stringy stuff on your private blog after all. If that is the case I'd truly regret it. I, for one, enjoyed seeing your contributions at the SCT.

Helge said...

Hi! You write, that non-commutative geometry is dead. Well the last thing I heard at my college was, that it is one of the most promising directions in theoretical physics. (I am studying physics).
So I am curious, what do you think, will be the direction of physics will take?

Robert said...


don't worry. I don't feel any bad sentiments towards the Coffee Table whatsoever. It's just that also want to have some physics content here (not just music and jigsaw puzzles). When I feel that a topic is appropriate for the coffee table I will post it there and when I think it fits better to this more personal space I will post it here.

Robert said...


non-commutative geometry was a hot topic in the string community after Seiberg and Witten's talks (and the following paper) at Strings '98 where (besides the SW-map) they followed up on work by Connes, Douglas, and Schwarz and Douglas and Hull. At that time. everybody was doing the non-commutative version of their hobby horse. Those days are over and many of the hep-th papers dealing with NCG are in my opinion on little side problems at best.

I was just surprised to see that so many people still devote their time to NCG but I am sure most of them do not think this will lead to the major breakthrough in high energy physics.

Plus I don't think there is any other area with so many papers with severe missconceptions or papers that are just plain wrong.

But still, it can be fun and sometimes you can learn from it when you regard the world as non-commutative.