D-strings and F-strings from string loops

TL;DR

The paper addresses how the low-energy string background fields, viewed as string condensates, require loop-induced worldsheet actions for D-strings and F-strings. By employing the Fischler-Susskind mechanism within a BRST framework, the authors derive loop-corrected field equations in type IIB that couple NS-NS and RR sectors to a D-string current, and show that these corrections can be encoded in an effective action with boundary terms. They then demonstrate that the D-string action, via a Hamiltonian path integral, yields a bound-state tension that is SL(2,Z) covariant and equivalent to an F-string action, thereby realizing the D-string/F-string duality in a unified description. The work provides a concrete worldsheet route to nonperturbative dualities, clarifies the role of loop effects in the effective action, and points toward extensions to membranes and M-theory membranes for broader nonperturbative insights.

Abstract

Since the background fields of the string low energy action are supposed to be the long range manifestation of a condensate of strings, the addition of world sheet actions to the low energy effective action needs some string theoretic explanation. In this paper we suggest that this may be understood, as being due to string loop effects. We first present arguments using an equation due to Tseytlin and then more rigorously in the particular case of type IIB theory by invoking the Fischler-Susskind effect. The argument provides further justification for ${\rm SL}(2,Z)$ duality between D-strings and F(fundamental)-strings. In an appendix we comment on recent attempts to relate the type IIA membrane to the 11-dimensional membrane.