Is the string field big enough?

Abstract

Cubic open string field theory uses a string field which can be roughly thought to represent the tangent space to the space of two-dimensional field theories at the point corresponding to a space-filling D-brane background. It is then natural to wonder if string backgrounds corresponding to field theories a finite distance away can be reached with this string field. In this lecture, I examine various case studies, including the tachyon vacuum, lower dimensional D-branes, marginal operators, and tachyon effective potentials, and argue that the string field is indeed large enough. Contribution to the proceedings of the workshop "The Quantum Structure of Spacetime and the Geometric Nature of Fundamental Interactions", Berlin, October 2000.