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About D-branes in type-II string theory

  1. Jun 7, 2007 #1
    I am trying to understand the best I can the d-brane theory. I have tried many sources and there is a thing which I don´t see totally clear, how the d-brane concept fit into type II superstring (no matter A or B).

    I mean, I can understand the argument that type II theories have in their massless spectrum antisymmetric fields and that that fields must arise from charged objects, and because hodge duality and all that the sources must be an extended object of the appropriate dimension.

    Also I believe that i rightly understand that you can represent the stringy one-loop amplitudes of type II theories by an efective supergravity action of point-like particles. That supersimmetry auctions (mainly their bosonic part) accept solitonic solutions that someway (which I don´t have totally clear) can be identified with the d-branes as described them before.

    Anyway, for me the big problem is how to fit the d-brane idea as expressed in any of the two forms i writed with the bosonic idea of the d-brane, that is, they are supposed to be hypersurfaces where the extremes of open strings must lie. But, of course, type II theories are closed strings, so that idea doesn´t seem to apply. Well, the solution most text say is "type II strings must have an open sector" but curiously I don´t see how these inclusion is actually realised. I guess that it can be related to a duality between type II theories and type I theory (which actually has open and closed strings, but I am aware that they are unoriented strings and that could be a problem) but I am not sure if i am right. Of course I know that all these is explained somewhere in many books of articles, but it is diversified over so many different chapters that it is a bit hard to follow he whole argumentation so if someone could explain all these I guess that not only me but a lot of people would be very acknowledged.
    Last edited: Jun 7, 2007
  2. jcsd
  3. Jun 7, 2007 #2
    My QM professor (Rob Leigh) was one of the discoverers of d-branes. I really enjoyed that class.
  4. Jun 8, 2007 #3


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    Sauron, see Sec. 2.3.2 D-brane interactions, of hep-th/0110055.
  5. Jun 30, 2007 #4
    Thanks for the link but I must say that it didn´t really seed too much light into the problem (or at least I didn´t understand the exact relevance).

    Recently, looking for string field theory, I found these very interesting paper:


    Seems like if, afther all, D-branes don´t fit in type I theorie exactly in the same way as they do in strings with an open sector, or at least I dont see an explicit construction of how the actual open sector for type II theories is implemented.

    Also I would like to answer you how you think that your ideas about the foundatios of string theory (the meaning of quantum function for the string) relates to the conventional aproachs of string field theories.
  6. Jul 2, 2007 #5


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    Well, my view is that string field theory is not the correct way to go. By the way, you certainly know that most of the great results in string theory is done without string field theory, as well as that superstring field theory does not (yet) seem to exist. You also know that perhaps the greatest success of string field theory is a solution of the tachyon problem of bosonic strings, but also that superstring theory is actually more conventional solution of the tachyon problem.

    In short, my current view is that string field theory is probably not correct, but I am open for different views as well. In particular, I will take a look at the paper you mention above.
  7. Jul 2, 2007 #6


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    Let me present one additional argument against string field theory. The main motivation for it is to derive the Feynman rules for calculating string scaterring amplitudes in a manner analogous to that in particle physics. Indeed, in particle physics, you cannot derive these rules by using only first quantization of free particles, which is why you need particle field theory in particle physics. However, the situation in string theory is completely different. All Feynman rules for string scaterring amplitudes CAN be derived from first quantization of free strings. From that point of view, there is no clear motivation for introducing string field theory at all.
  8. Jul 2, 2007 #7
    I am not sure if, as you say, Feynman rules can be derived from firts quantization. As I see it in most of texts that rules are proposed ad hoc based in a formal simlarity with the point particle case.

    About the non existence of superstring field theory I did a search and I found the Berkovits model http://arxiv.org/PS_cache/hep-th/pdf/9503/9503099v1.pdf

    The paper is from the 1995 but I saw it cited in a mucho more recent paper and semmengly there was not problem with it.

    Anyway I am just begining to study SFT and my motivation was preciselly that I don´t find too convicing the justifications of the Polyakov prescription, For example I don´t see a clear reason why you couldn´t get knotted states of strings if, for example, an open string join it´s ends inside of a closed one. Well, in fact I have readed in the divulgative book of Susskind ("the cosmic landscape") that an strings can cross another, but he gives no argumentation of it and I neither see an easy way to deduce it from the first quantization lagrangian and the whole perturbation theory which simply seems to accept it as an postulate.

    Another motivation for SFT, a more ortodoux one, would be the deduction of some rule for string compactifications and in that way it could seed some light in the landscape.
  9. Jul 3, 2007 #8


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    There are TWO approaches to Feynam rules in string theory. One is more practical and more ad hoc, corresponding to Secs. 7 and 8 of the Green-Shwarz-Witten textbook. You clearly have this in mind. But there is also another approach that is less practical but derived from first principles, corresponding to Sec. 11 of this textbook. Of course, both approaches are equivalent. What is even more important, even if you use the ad hoc rules of the first approach, you cannot deny that the rules are unique, i.e., that there are no different possibilities for different types of interactions as in particle field theory.

    Concerning the Berkovits model, I have seen claims that there are problems with it, but I don't remember where exactly I have seen that and what exactly the problems are.
  10. Aug 9, 2007 #9
    First, thanks for the advice on that particular chapter of the GSW book, I have found it very interesting.

    Appart to say that I have continuated indagating about the original question of the thread and at last I gave with concrete answers. I think that you could find some of them interesting. Instead of giving here a very long question I leave a link to a post in my humble journal (links to the orignal paplers there) about the subject: http://freelance-quantum-gravity.blogspot.com/2007/08/case-for-d-branes-in-closed-strings.html

    The key words to the apropiate answer was "boundary states", a formalism related to conformal field theories.
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