Interactions involving D-branes

TL;DR

This paper explores the spectrum and interactions of D-branes, demonstrating how collections of D-strings behave like multiply wound strings, and analyzes decay processes and absorption cross sections using dualities and classical analogies.

Contribution

It reveals the behavior of D-branes under large dilaton values and establishes duality-based decay amplitudes and absorption cross sections consistent with classical models.

Findings

D-strings behave as multiply wound strings at large dilaton values

Decay of excited D-strings matches duality-based calculations

Absorption cross sections align with classical black hole models

Abstract

We investigate some aspects of the spectrum of D-branes and their interactions with closed strings. As argued earlier, a collection of many D-strings behaves, at large dilaton values, as a single multiply wound string. We use this result and T-duality transformations to show that a similar phenomenon occurs for effective strings produced by wrapping p-branes on a small (p-1)-dimensional torus, for suitable coupling. To understand the decay of an excited D-string at large dilaton values, we study the decay of an elementary string at small dilaton values. A long string, multiply wound on a circle, with a small excitation energy is found to predominantly decay into another string with the same winding number and an unwound closed string (rather than two wound strings). This decay amplitude agrees, under duality, with the decay amplitude computed using the Born-Infeld action for the D-string. We compute the absorption cross section for the D-brane model studied by Callan and Maldacena. The absorption cross section for the dilaton equals that for the scalars obtained by reduction of the graviton, and both agree with the cross section expected from a classical hole with the same charges.