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R.X.
R.X. is offline
#11
Mar14-04, 01:15 PM
P: 37
Originally posted by Urs
R.X. wrote:



Are you referring to Greene or to Kaku here?

Neither, nor - the thread is about Marolf's review and this is what I meant - a quite biased selection of topics, with no clear idea why some subjects he presents should be more important than others that he leaves out.

Since you brought up other names: what I wrote applies also, more or less, to Kaku as well.


Originally posted by Urs

Could you summarize the main ideas and results of this work?
Douglas initiated a program to understand the quantum properties of D-branes, starting from the appropriate mathematical formulation (which is in terms of derived categories). This is a bit complicated stuff, but conceptionally extremely important, and I mean this physicswise. Since it is not fashionable to work on it, not much attention has been paid to this subject, but unfairly so.

I would say that many if not most of those more phenomenologically oriented papers, on brane models and alike, are pretty off the track and sometimes even outright wrong, just because they do not take effects into account which we know from Douglas' work.

For example, many papers assume (in the context of a given brane model), that a brane-anti-brane pair breaks supersymmetry due to the tachyonic mode between them. They use this to feed some degree of SUSY breaking into their models. But we known from Douglas' work (via his concept of flow of gradings), that if you take the quantum geometry of those brane properly into account, then the notion of what a brane is and what an anti-brane is, is not a universal notion but depends on where you are in the moduli space. It generically so happens that a naive supersymmetry-breaking brane-antibrane pair turns into a susy preserving brane-brane pair in some other region of the moduli space.

In other words, from the effective action point of view, the naive brane-anti-brane system has a non-perturbative potential with a susy restoring minimum, somewhere in the moduli space.
This is probably not what the unsuspecting brane model builders had in mind... and they cannot know it if they didn't read Douglas' papers.

Summa summarum, it just doesn't make sense to attempt any sort of brane model building, without the knowledge of such effects. Admittedly, this is mathematically very complicated stuff, and this is why only few people know about it - most others go the easy way and ignore it.

Marolf's review does not mention this conceptionally important subject, as well as many other's work. As said, he is not an insider of these matters and probably doesn't know better. A priori, one may just not care, but the effect of such a review is that newcomers to the field get a biased impression of what is important to study and work on, and what not.

Certainly, what is important to study and what not,
could be debated over and is to some extent a matter of taste, but there is a limit of what is reasonable, especially for a review which claims to be a guide to the field. For example, mentioning non-BPS states as an important subject while leaving out the whole of Vafa's recent work is just outrageous.