Higher-spin kinematics & no ghosts on quantum space-time in Yang-Mills matrix models

TL;DR

This paper classifies higher-spin modes in a quantum space-time from the IIB matrix model, establishing a no-ghost theorem and linking the model to a consistent quantum gravity theory in 3+1 dimensions.

Contribution

It provides a detailed classification of bosonic higher-spin modes, including off-shell modes previously missing, and demonstrates the absence of ghosts in the quantum space-time framework.

Findings

Establishment of a no-ghost theorem for higher-spin modes.

Identification of two towers of on-shell higher-spin modes.

Derivation of the full propagator governed by an effective metric.

Abstract

A classification of bosonic on- and off-shell modes on a cosmological quantum space-time solution of the IIB matrix model is given, which leads to a higher-spin gauge theory. In particular, the no-ghost-theorem is established. The physical on-shell modes consist of 2 towers of higher-spin modes, which are effectively massless but include would-be massive degrees of freedom. The off-shell modes consist of 4 towers of higher-spin modes, one of which was missing previously. The noncommutativity leads to a cutoff in spin, which disappears in the semi-classical limit. An explicit basis allows to obtain the full propagator, which is governed by a universal effective metric. The physical metric fluctuations arise from would-be massive spin 2 modes, which were previously shown to include the linearized Schwarzschild solution. Due to the relation with ${\cal N}=4$ super-Yang-Mills, this is expected to define a consistent quantum theory in 3+1 dimensions, which includes gravity.