Non-perturbative materialization of ghosts

TL;DR

This paper investigates non-perturbative decay processes involving ghost matter in gravity theories, calculating instantons and their actions, and concludes such processes can be suppressed in realistic models.

Contribution

It introduces a non-perturbative analysis of ghost matter nucleation via instantons, expanding understanding beyond perturbative decay rates.

Findings

Instantons for ghost nucleation are identified and their Euclidean actions computed.

Some instantons induce topology change or have negative Euclidean action.

Non-perturbative ghost nucleation can be suppressed in phenomenological scenarios.

Abstract

In theories with a hidden ghost sector that couples to visible matter through gravity only, empty space can decay into ghosts and ordinary matter by graviton exchange. Perturbatively, such processes can be very slow provided that the gravity sector violates Lorentz invariance above some cut-off scale. Here, we investigate non-perturbative decay processes involving ghosts, such as the spontaneous creation of self-gravitating lumps of ghost matter, as well as pairs of Bondi dipoles (i.e., lumps of ghost matter chasing after positive energy objects). We find the corresponding instantons and calculate their Euclidean action. In some cases, the instantons induce topology change or have negative Euclidean action. To shed some light on the meaning of such peculiarities, we also consider the nucleation of concentrical domain walls of ordinary and ghost matter, where the Euclidean calculation can be compared with the canonical (Lorentzian) description of tunneling. We conclude that non-perturbative ghost nucleation processes can be safely suppressed in phenomenological scenarios.