Boundary states as exact solutions of (vacuum) closed string field theory

TL;DR

This paper demonstrates that boundary states are exact solutions in vacuum closed string field theory, satisfying an idempotency relation that encodes the equations of motion and reproduces open string spectra.

Contribution

It establishes boundary states as exact solutions in closed string field theory and links their idempotency to the theory's equations of motion.

Findings

Boundary states satisfy B*B=B in HIKKO's closed string field theory.

Variations around boundary states reproduce open string spectra.

Idempotency relation may serve as the vacuum equation of motion.

Abstract

We show that the boundary states are idempotent B*B=B with respect to the star product of HIKKO type closed string field theory. Variations around the boundary state correctly reproduce the open string spectrum with the gauge symmetry. We explicitly demonstrate it for the tachyonic and massless vector modes. The idempotency relation may be regarded as the equation of motion of closed string field theory at a possible vacuum.