Mixed Boundary Conditions and Brane-String Bound States

TL;DR

This paper investigates open strings with mixed boundary conditions, revealing their endpoints form bound states of D-branes with fundamental strings, which are BPS saturated and consistent with supergravity and effective field theory predictions.

Contribution

It demonstrates that open strings with mixed boundary conditions can form BPS bound states of D-branes and fundamental strings, extending to multiple strings using Chan-Paton factors.

Findings

Bound states are BPS saturated.

Mass densities agree with SL(2,Z) invariant supergravity.

Results extend to multiple D-strings and F-strings.

Abstract

In this article we consider open strings with mixed boundary conditions (a combination of Neumann and Dirichlet conditions at each end). We discuss how their end points show a $D_p$-brane with NS-NS charge, i.e. a bound state of a D-brane with a fundamental strings. We show that these branes are BPS saturated. In the case of one-branes, we show that their mass densities are in agreement with IIb SUGRA which is Sl(2,Z) invariant. Using Chan-Paton factors, we extend our results to the case of bound states of $n$ D-strings and $m$ F-strings. These string theoretic results are also checked in the effective field theory limit.