# What is NS5 brane?

NS5 brane can be considered as 1/2 BPS solution in supergravity (with other solutions to compare):

This branes of Type IIA/B supergravity are expected to extend to solutions of the full Type IIA/B string equations.

The NS5 brane indeed very much behave as large size semi-classical solitons, whose energy depends on the string coupling via $$1/g^2_s$$, as is familiar from solitons in quantum field theory.

In contrast, in the weak-coupling limit, the D-brane solution of supergravity reduces to a localized defect in flat space-time, that gives us boundary condition on the string dynamics.

But I wanna to understand more about NS5 branes.

1. What is role of such objects in string theory?

2. Which d.o.f. are related to such objects?

3. Is some effective theory, that describe dynamics of such objects? Is it Namby-Goto action for brane or some kind of DBI action?

• This is really really broad. (Except for your question 3, which is immediately answered by a search for "ns5 brane effective action".) – user21299 Apr 17 '20 at 20:28
• @alexarvanitakis, could you answer in post with concrete formulas for actions and references? (Maybe I haven't enough knowledge to understand results of search) – Nikita Apr 17 '20 at 20:46
• arxiv.org/abs/hep-th/9806169 formula (2.10) for the NS5 brane on type IIB. First search hit, for me at least. – user21299 Apr 17 '20 at 20:57