As far as I understand, the branes of brane cosmology are lower-dimensional "sub-manifolds" of some space. It was hard to imagine for me how such structure could exist and be physical. But then I learned of topological defects, which are essentially that. So my question is:

Question: Are the branes of brane cosmology supposed to be topological defects of some sort? If not, how else could a "sub-manifold" be something physical?

I also posed a related question which received little attention. Please note that I have only an undergraduate understanding of physics, but are fine with advanced mathematics.

  • $\begingroup$ point particle is a 0-brane. It may or may not be topological, depending on its theory. $\endgroup$
    – Kosm
    Commented Aug 30, 2023 at 13:12
  • $\begingroup$ @Kosm Does this apply to higher-dimensional branes as well? Are they considered as defects in some theories and as unexplained fundamental objects in others? $\endgroup$
    – M. Winter
    Commented Aug 30, 2023 at 13:30
  • $\begingroup$ yes, they are just generalizations of point particles. For example D branes are objects on which open strings of string theory end, so they are not fundamental like strings. And in effective low-energy field theory, they can be described as topological solitons in principle. $\endgroup$
    – Kosm
    Commented Aug 31, 2023 at 6:34
  • $\begingroup$ solitons of one theory can be described as "fundamental" particles in the dual theory - see electric-magnetic duality, or S-duality. So, the same would in general apply to branes. Depending on the description, they could be fundamental or topological. $\endgroup$
    – Kosm
    Commented Aug 31, 2023 at 6:37


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