I decided recently (to try) to learn String Theory, however from the beginning some newbie questions came up, which haven't given me a break. For this reason, I decided to ask some of them. I'd prefer to start with a relatively sensible one, because probably I'll make fun of myself, if I ask my grand query. So the thing, which I'd like to know, is:

Is there a difference between closed strings and open ones attached to a $D_{0}$ - brane (say for consistency - in a Type IIA theory) and if yes, what it is?


1 Answer 1


A simple way to see why the systems you describe are not identical is to recognize that a $D0$ brane carries R-R charge which sources a one-form potential, while the closed string is uncharged.

  • $\begingroup$ What if the closed string is represented as a pair of open ones, attached to "opposite" D0-branes, whose Ramond potentials (hypotetically) cancel? $\endgroup$
    – Newbie
    Dec 3, 2014 at 13:46
  • $\begingroup$ @JustAsking: The potentials will not cancel everywhere. The system would be similar to a dipole in electrostatics, which has non-vanishing potential and field-strength. $\endgroup$ Dec 3, 2014 at 14:08
  • $\begingroup$ This is so, indeed. However, if hypotetically there was a way to cancel the potentials - not necessarily in the way I described, but e.g. by intersecting "bigger" (than D0) branes - would it be true that closed strings can be perceived as compositions of open ones, attached to each other? The point, I'm aiming for, is whether it is true that gravity interactions between open strings can be "represented" via a (suitable) intersection of the branes thay are glued to, or an exchange of closed 2-spin strings is inevitably necessary? $\endgroup$
    – Newbie
    Dec 3, 2014 at 19:50

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