Exorcizing Ghosts from the Vacuum Spectra in String-inspired Nonlocal Tachyon Condensation

TL;DR

This paper introduces a novel weakly nonlocal deformation of local quantum field theories that enables ghost-free tachyon condensation, with potential applications in spontaneous symmetry breaking in fundamental physics.

Contribution

It proposes a new Lorentz and gauge covariant star-product framework that achieves ghost-free tachyon condensation without ghosts at the perturbative level.

Findings

Successfully avoids ghosts in tachyon condensation models

Provides a new mathematical framework for nonlocal QFTs

Potential applications in spontaneous symmetry breaking

Abstract

Tachyon condensation in quantum field theory (QFT) plays a central role in models of fundamental interactions and cosmology. Inspired by tower truncation in string field theory, ultraviolet completions were proposed with infinite-derivative form factors that preclude the appearance of pathological ghosts in the particle spectrum, contrary to other local higher-derivative QFT's. However, if the infinite-derivative QFT exhibits other vacua, each of them has its own spectrum, which is generally not ghost-free: an infinite tower of ghost-like resonances pops up above the nonlocal scale at tree-level, whose consistency is unclear. In this article, a new weakly nonlocal deformation of a generic local QFT is introduced via a Lorentz and gauge covariant star-product of fields, which is commutative but nonassociative in general. This framework realizes tachyon condensation without ghosts at the perturbative level, with applications for spontaneous symmetry breaking.