Unitarity of noncommutative field theories from string theory

TL;DR

This paper investigates the unitarity issues in noncommutative quantum field theories derived from string theory, analyzing the emergence of tachyonic instabilities and their dependence on string and brane parameters.

Contribution

It demonstrates the universality of the unitarity violation mechanism in noncommutative theories from string theory and explores implications for superstring theory and NCOS limits.

Findings

Tachyonic branch cuts appear when the Seiberg-Witten limit is applied.

The unitarity violation depends on the brane-worldvolume dimension.

Discussion of potential proofs within superstring theory and NCOS framework.

Abstract

We improve the study of the lack of perturbative unitarity of noncommutative space-time quantum field theories derived from open string theory in electric backgrounds, enforcing the universality of the mechanism by which a tachyonic branch cut appears when the Seiberg-Witten limit freezes the string in an unstable vacuum. The main example is realized in the context of the on-shell four-tachyon amplitude of the bosonic string, and the dependence of the phenomenon on the brane-worldvolume dimension is analysed. We discuss the possibility of a proof in superstring theory, and finally mention the NCOS limit in this framework.