Exactly Soluble Dynamics of (p,q) String Near Macroscopic Fundamental Strings

TL;DR

This paper presents an exactly solvable model of (p,q) string dynamics near macroscopic fundamental strings, revealing novel features of open string radion rolling and decoupling phenomena in a controlled supergravity background.

Contribution

It introduces an exactly solvable analog for open string tachyon rolling dynamics in a supergravity background, with new insights into string interactions and electric field behavior.

Findings

Open string radion dynamics are exactly solvable in this setup.

The worldsheet electric field increases monotonically to the critical value.

D string constituents decouple near the background string.

Abstract

We study dynamics of Type IIB bound-state of a Dirichlet string and n fundamental strings in the background of N fundamental strings. Because of supergravity potential, the bound-state string is pulled to the background fundamental strings, whose motion is described by open string rolling radion field. The string coupling can be made controllably weak and, in the limit $1 << g^2_{\rm st} n << g^2_{\rm st} N$, the bound-state energy involved is small compared to the string scale. We thus propose rolling dynamics of open string radion in this system as an exactly solvable analog for rolling dynamics of open string tachyon in decaying D-brane. The dynamics bears a novel feature that the worldsheet electric field increases monotonically to the critical value as the bound-state string falls into the background string. Close to the background string, D string constituent inside the bound-state string decouples from fundamental string constituents.