String Field Equations from Generalized Sigma Model

TL;DR

This paper introduces a novel method to derive string field equations from a generalized sigma model, combining renormalization group and covariant beta function techniques, applicable to various string excitations.

Contribution

It presents a covariant approach that unifies features of existing methods to derive string field equations from sigma models, applicable to multiple string excitation levels.

Findings

Reproduces the correct spectrum of a left-right symmetric bosonic string.

Derives consistent equations for tachyon, massless, and first massive levels.

Maintains covariance under broad local and non-local transformations.

Abstract

We propose a new approach for deriving the string field equations from a general sigma model on the world sheet. This approach leads to an equation which combines some of the attractive features of both the renormalization group method and the covariant beta function treatment of the massless excitations. It has the advantage of being covariant under a very general set of both local and non-local transformations in the field space. We apply it to the tachyon, massless and first massive level, and show that the resulting field equations reproduce the correct spectrum of a left-right symmetric bosonic string.