Dissipative stabilization of Ostrogradsky modes in non-equilibrium field theory

TL;DR

This paper explores how dissipative effects in open quantum systems can suppress Ostrogradsky ghosts in higher-derivative field theories, revealing phase transitions and mechanisms for stabilization.

Contribution

It introduces a non-equilibrium framework using the Keldysh-Lindblad approach to demonstrate dissipative stabilization of Ostrogradsky modes.

Findings

Dissipative baths generate effective masses and widths for ghost sectors.

A critical coupling induces a phase transition with bifurcated dissipative branches.

Dissipative dynamics can suppress ghost excitations via mass generation or overdamping.

Abstract

In this work, we investigate higher-derivative quantum field theories and the problem of Ostrogradsky instability within an open-system Keldysh-Lindblad framework. Coupling the ghost sector to dissipative baths generates non-perturbative effective masses and dissipative widths through self-consistent gap equations. Above a critical coupling, the nonequilibrium dynamics develops bifurcated dissipative branches, signaling the emergence of a dissipative phase transition and a nontrivial critical structure in parameter space. We find that the resulting dissipative dynamics can suppress ghost excitations through two distinct mechanisms: in one branch, a large dynamically generated effective mass preserves a quasiparticle-like excitation, while in the second branch, strong dissipative broadening destroys the quasiparticle character through overdamped dynamics. Our results suggest that dissipative effects may provide a nonequilibrium mechanism for the spectral suppression of Ostrogradsky ghosts. The comparison with the healthy sector indicates that the stabilization mechanism is intrinsically tied to the ghost-like spectral structure.