# Converting open strings to closed strings

#### eNathan

Is it possible to convert open strings to closed strings in string theory. Perhaps, we can convert out rest mass into gravitons, and appear in other dimensions. Is this a possibility? Or does string theory not predict this behavior?

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#### Berislav

I am as newbie as they get when it comes to string theory. But, as far as I know open and closed strings differ by the boundary conditions imposed on the string function $X^\mu(\sigma,\tau)$. The Dirichlet boundary conditions are imposed so that the endpoints do not "move" (e.g, the string ties two very heavy quarks). The Neumann boundary conditions allow movement (e.g, the string ties two light quarks). I fail to see how transforming one type into another would allow us to apper in other dimensions.

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eNathan said:
Is it possible to convert open strings to closed strings in string theory. Perhaps, we can convert out rest mass into gravitons, and appear in other dimensions. Is this a possibility? Or does string theory not predict this behavior?
Open strings freely convert into closed strings and vice versa. This is analogous to particles interacting via processes described by feynmann diagrams.

These are bosonic strings; you evidently think that the distinction fermion/boson corresponds to open/closed. I suspect this comes from popular accounts of the boundary/bulk theory of why gravity is weak compared to the other forces.

However the distinction is between bosonic strngs, which produce no fermions at all, and superstrings, which can do both fermions and bosons. The graviton is the only "familiar" particle that bosonic strings produce; the structures of the standard model, where they are approximately realized by stringy constuctions are all from superstrings. So the boundary/bulk theory has superstrings that are confined to the boundary and bosonic closed graviton producing strings that aren't.

#### Jek570

thank you VERY MUCH for making and answering this thread!!! Sorry for bringing back a deceased thread!

#### FalseVaccum89

These are bosonic strings; you evidently think that the distinction fermion/boson corresponds to open/closed. I suspect this comes from popular accounts of the boundary/bulk theory of why gravity is weak compared to the other forces.
It would be nice if they would make this distinction in the popular accounts! If I hadn't read more technical (semi-popular would be a better term) works on the subject, I wouldn't have had any idea what you're talking about. There's a semi-popular book by a guy named Gasperini on pre-Big Bang superstring cosmology that specifies the difference between the bosonic string and superstrings.

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