On the curious spectrum of duality invariant higher-derivative gravity

TL;DR

This paper investigates the spectrum of a duality-invariant higher-derivative double field theory, revealing massive ghosts, scalars, and an enhanced gauge symmetry in the tensionless limit, and introduces a ghost-free massive extension.

Contribution

It provides a detailed spectral analysis of a duality-invariant higher-derivative theory and proposes a new ghost-free massive extension with a novel mass term.

Findings

Spectrum includes massive spin-2 ghosts and scalars

Massless limit is non-singular with enhanced gauge symmetry

Proposes a ghost-free massive extension of the theory

Abstract

We analyze the spectrum of the exactly duality and gauge invariant higher-derivative double field theory. While this theory is based on a chiral CFT and does not correspond to a standard string theory, our analysis illuminates a number of issues central in string theory. The full quadratic action is rewritten as a two-derivative theory with additional fields. This allows for a simple analysis of the spectrum, which contains two massive spin-2 ghosts and massive scalars, in addition to the massless fields. Moreover, in this formulation, the massless or tensionless limit $\alpha'\rightarrow \infty$ is non-singular and leads to an enhanced gauge symmetry. We show that the massive modes can be integrated out exactly at the quadratic level, leading to an infinite series of higher-derivative corrections. Finally, we present a ghost-free massive extension of linearized double field theory, which employs a novel mass term for the dilaton and metric.