Gauge-invariant action for free string field theory with boundary

TL;DR

This paper develops a gauge-invariant action framework for open and closed string field theories on spaces with boundaries, incorporating boundary degrees of freedom and ensuring consistency via the BV formalism.

Contribution

It introduces a novel gauge-invariant kinetic action for string fields with boundary conditions, including a BV master action and explicit free actions for various string modes.

Findings

Successfully constructs gauge-invariant kinetic terms for boundary string theories.

Derives BV master action satisfying the master equation.

Provides explicit free actions for massless and massive string modes in boundary backgrounds.

Abstract

We construct fully gauge-invariant kinetic terms for open and closed string field theories on a target space with boundary. This is realized by promoting the gauge parameters at the boundary to extra dynamical modes describing boundary degrees of freedom. Having a gauge-invariant classical action, we also construct the corresponding BV master action and show that the master equation is obeyed thanks to a peculiar nilpotent structure of the BV kinetic operator. From this general construction we explicitly derive free actions for massless and massive modes of open and closed strings propagating on a target with a boundary, including linear-dilaton backgrounds.