New answers tagged branes
The counting of the dimensions is the same for D1-branes and the fundamental F1-strings. There are 24 physical scalars because the embedding of a 2-dimensional world sheet (of either F-string or D-string) may be locally specified by 24 functions. For example, as long as the coordinates $X^0,X^1$ are changing at least "a little bit" in a region of the world ...
I'm no expert on the subject, but according to one of the proponents of this model (http://wwwphy.princeton.edu/~steinh/npr/), the 2 branes "stick" to create the universe. Hope that helps.
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