The closed string tadpole in open string field theory

TL;DR

This paper investigates gauge invariant observables in open string field theory, revealing their relation to closed-string tadpoles and proposing a general argument for this connection, with extensions to superstring theory.

Contribution

It demonstrates a universal relation between gauge invariant observables and closed-string tadpoles, and extends the analysis to Berkovits superstring field theory.

Findings

Gauge invariants relate to closed-string tadpoles on disks.

The relation holds for marginal solutions and the tachyon vacuum.

Extension to superstring field theory discussed.

Abstract

We compute a class of gauge invariant observables for marginal solutions and the tachyon vacuum. In each case we find that the observables are related in a simple way to the closed-string tadpole on a disk with appropriate boundary conditions. We give a sketch of an argument that this result should hold in general using the BRST invariance of the closed string two-point function. Finally, we discuss the analogous set of invariants in the Berkovits superstring field theory.