# Understanding string theory branes

I've been looking into string theory, and I understand the $D1$ strings, but I find the concept of branes confusing. Are they just $D2$ strings? Or are they woven constructs made out of many $D1$ strings?

• What do you mean by a "$d_1$-string" or a "$d_2$-string"? Do you mean what's more commonly called a $D_p$ (or Dirichlet) brane? What would it mean to "weave" $d_1$ strings? Can you be more precise what exactly you have read about branes, and what you want to know? – ACuriousMind Oct 24 '17 at 14:47
• @ACuriousMind the $d_x$ notation refers to dimension, and by woven I mean rotating around each other similar to fibers in clothe, creating a structure – mcchucklezz Oct 24 '17 at 14:49
• That doesn't make any sense in string theory's formalism. Are you just asking whether branes are "made of" something or are fundamental objects? Maybe these answers of mine are of interest to you: physics.stackexchange.com/a/348427/50583, physics.stackexchange.com/a/278737/50583 – ACuriousMind Oct 24 '17 at 14:53

## 1 Answer

A $p$-brane is an object which sweeps out a world volume of spatial dimension $p$. Since a string will sweep out a world sheet with a temporal and spatial coordinate $(\tau, \sigma)$, a $1$-brane is a string.

$p$-branes for $p\geq 2$ are soliton solutions to the equations of motion of low energy theories derived from string theory, such as type $\mathrm{IIA}$ or $\mathrm{IIB}$ theory.

Now, a $D$-brane specifically refers to a brane which is used to specify Dirichlet boundary conditions for an open string. There is some differing convention: a $\mathrm{D}p$-brane may refer to what in the present convention is a $p$-brane, or a $(p-1)$-brane.

More deeply, through dualities, it may be shown that $p$-branes are generally related to the perturbative string. For more on this, I'd recommend Introduction to Strings and Branes by West. This is probably what you're looking for - it's the closest I can imagine to your description of weaving higher dimensional branes from the fundamental string.

• So would this mean that strings can be in various numbers of dimensions? – mcchucklezz Oct 24 '17 at 17:16
• @script8man No, branes can be in various numbers of dimensions. A string is a brane of a specific dimension. – JamalS Oct 24 '17 at 18:21