# D-branes and closed strings

1. Feb 17, 2009

### Demystifier

By definition, D(irichle)-branes are branes on which open strings end. Then how closed string theories IIA and IIB may contain D-branes? Or more precisely, why the branes appearing in closed string theories are still called D-branes?

2. Feb 20, 2009

### Demystifier

Come on, is it possible that nobody knows the answer?
If so, it would also help if someone would say that he/she is also puzzled with this.

3. Feb 20, 2009

### MTd2

Hmm, here it goes a guess. The only way to connect a D brane with a closed string is by attaching all the closed circle with the D-Brane. Since this is the time-like dimension, or the endline of worldsheet 'pant', you can see that closed strings will only connect branes in a time-like manner, you can say that they will be moving and connecting branes to branes. So, closed strings will be the particles with which the branes interacts with each other. This is why when we are talking about the Type IIB version of string theory, string theory peopole frequently talk about ads/cft, because IIB is a superstring picture that clearly shows gravitational relations, or, interactions between strings.

Thinking about 'pants', or cobordism, the open strings would be 'ortogonal' to this, so, and exchange of closed strings would be more or less equivalent to stretching open strings.When people talk about N coincident branes, a more precise picture is achieved by adding a B anticomutative to the open strings connecting the branes. This field reduces the minimum energy stable energy along the aligning dimension, this is like the branes were being geometricaly deformed along this dimension. This is a sign of some kind of gravitational attraction between branes. And gravity is more clearly present in the IIB version.

Last edited: Feb 20, 2009
4. Feb 20, 2009

### MTd2

Note that this is just a guess, I really don't understand these things at all...

5. Feb 20, 2009

### Demystifier

So essentially, is this because a closed string (without a loop) is dual to an open string (with a loop)?

6. Feb 20, 2009

### MTd2

Well, I guess so... Not sure though.

Last edited: Feb 20, 2009
7. Feb 20, 2009

### Sauron

The way D-ranes are usually related to type II is by means of the Ramond-Ramond fields that appear in the perturbative spectrum of stthat string theories. You need a source for that fields and it sis simple to see that point particles or on-dimensional strings can´t source them. Dp-branes, of apropiate dimensions.

Certainly this doesnt too much correspond they way the D-branes are incorporated in the bosonic string picture. If you read the original papers of Polchinsky you will se that he mentions an open string sector in the hilbert space of the type-II strings.

B.T.W. I made the same question some time ago in this phorum, try to search and see the answers there.

8. Feb 20, 2009

### MTd2

I see, so the strings couple to branes through the perturbative spectrum, like, in the perturbative spectrum, depending on the order and symmetry or anti-symmetry of the p form, it can couple to a variety of p branges.

But I would like to know if the antisymmetric modes are related to the type I with non commutative background B field.

9. Feb 20, 2009

### MTd2

10. Feb 21, 2009

### jdstokes

I had the same question a while ago but never really got to the bottom of it (since these things tend to be quite deep).

My understanding is that D-branes in IIB string theory are identified with black p-branes which occur as solitonic solutions of IIB supergravity. The basic idea is that the ends of open strings ending on the D-brane can meet, forming a closed string which can leave the brane and vice-versa. Thus, open strings in IIB are a non-perturbative effect whereas they are already there perturbatively in e.g. Type I ST.

11. Feb 23, 2009