Re: D-branes and K-theory

Volker Braun <[EMAIL PROTECTED]> wrote in message
news:<[EMAIL PROTECTED]>...
> On Thu, 20 Nov 2003 22:36:58 +0300, Squark wrote:
> > 1) On p. 14 he talks about the "p-brane charge" associated with
> > a U(1) gauge field on a line bundle L. How is that defined?
>
> At that point he's talking about the physical charge - the goal of the
> whole chapter is to define precisely that in mathematical terms.
>
> Of course that has something to do with its K-class / first chern class
> but you're rushing ahead...

I don't agree, see my reply to Aaron.

> > 2) On p. 18 Wittens mentions the notion of a "twisted bundle" i.e. an
> > object with transition functions that generate a non-trivial two-cocycle
> > (an element of H(Z, Z_2), where Z is the space upon which the bundle is
> > defined). I wonder whether such a "bundle" can be thought of as a
> > section of a non-trivial 2-bundle (gerb)?
>
> No! There is no B-field / twisted K-theory / gerbe on page 18, this is
> only later.

I realize that. However, it appears branes wrapped on submanifolds Z
with nonvanishing W_3(Z) carry a twisted gauge bundle (on Z). Does it
mean an effective B-field appears when we restrict to Z? This is very odd.


Best regards,
 Squark

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