String Field Theory Solution for Any Open String Background

TL;DR

This paper presents an exact, versatile solution in open bosonic string field theory capable of describing various static open string backgrounds, confirming key conjectures and demonstrating background independence.

Contribution

It introduces a general solution using boundary condition changing operators, enabling the description of diverse backgrounds and providing explicit examples of D-brane configurations.

Findings

Proves Sen's second conjecture about tachyon condensation.

Constructs multiple D-brane solutions with different gauge groups.

Provides a nonperturbative proof of background independence.

Abstract

We present an exact solution of open bosonic string field theory which can be used to describe any time-independent open string background. The solution generalizes an earlier construction of Kiermaier, Okawa, and Soler, and assumes the existence of boundary condition changing operators with nonsingular OPEs and vanishing conformal dimension. Our main observation is that boundary condition changing operators of this kind can describe nearly any open string background provided the background shift is accompanied by a timelike Wilson line of sufficient strength. As an application we analyze the tachyon lump describing the formation of a D$(p-1)$-brane in the string field theory of a D$p$-brane, for generic compactification radius. This not only provides a proof of Sen's second conjecture, but also gives explicit examples of higher energy solutions, confirming analytically that string field theory can "reverse" the direction of the worldsheet RG flow. We also find multiple D-brane solutions, demonstrating that string field theory can add Chan-Paton factors and change the rank of the gauge group. Finally, we show how the solution provides a remarkably simple and nonperturbative proof of the background independence of open bosonic string field theory.