Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Living with the Wrong Sign

Patrick Cooper, Sergei Dubovsky, Ali Mohsen

TL;DR

This paper investigates whether a Lorentz-invariant, UV-complete theory can accommodate superluminal propagation by flipping the sign of a leading higher-dimensional operator in a two-dimensional string-inspired model. It constructs an exact S-matrix with a 'wrong sign' phase shift, analyzes its integrability, and examines its thermodynamics, finite-volume spectrum, and cosmological backgrounds. The results show on-shell amplitudes are well-behaved while off-shell locality remains ambiguous, with intriguing features such as absence of Hagedorn growth and a spectrum containing states with imaginary energy, indicating subtle consistency conditions. The work highlights how gravitational theories can occupy an intermediate position between conventional QFTs and EFTs and motivates further exploration of UV completions beyond standard locality.

Abstract

We describe a UV complete asymptotically fragile Lorentz-invariant theory exhibiting superluminal signal propagation. Its low energy effective action contains "wrong" sign higher dimensional operators. Nevertheless, the theory gives rise to an S-matrix, which is defined at all energies. As expected for a non-local theory, the corresponding scattering amplitudes are not exponentially bounded on the physical sheet, but otherwise are healthy. We study some of the physical consequences of this S-matrix.

Living with the Wrong Sign

TL;DR

This paper investigates whether a Lorentz-invariant, UV-complete theory can accommodate superluminal propagation by flipping the sign of a leading higher-dimensional operator in a two-dimensional string-inspired model. It constructs an exact S-matrix with a 'wrong sign' phase shift, analyzes its integrability, and examines its thermodynamics, finite-volume spectrum, and cosmological backgrounds. The results show on-shell amplitudes are well-behaved while off-shell locality remains ambiguous, with intriguing features such as absence of Hagedorn growth and a spectrum containing states with imaginary energy, indicating subtle consistency conditions. The work highlights how gravitational theories can occupy an intermediate position between conventional QFTs and EFTs and motivates further exploration of UV completions beyond standard locality.

Abstract

We describe a UV complete asymptotically fragile Lorentz-invariant theory exhibiting superluminal signal propagation. Its low energy effective action contains "wrong" sign higher dimensional operators. Nevertheless, the theory gives rise to an S-matrix, which is defined at all energies. As expected for a non-local theory, the corresponding scattering amplitudes are not exponentially bounded on the physical sheet, but otherwise are healthy. We study some of the physical consequences of this S-matrix.

Paper Structure

This paper contains 7 sections, 35 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Description of the setup
  3. Classical Time Advance
  4. Thermodynamics and Finite Volume Spectrum
  5. Cosmology
  6. Discussion
  7. Acknowledgements

Figures (1)

  • Figure 1: Above is a plot of the region where energy becomes imaginary. Blue and green are at $D = 2$, $R/l_s = 10$ and $20$ respectively. Red and Yellow are at D = 62, $R/l_s = 10$ and $20$ respectively. The allowed region is the left of each curve.