For two interacting scalar fields, low-energy ghosts are equivalent to tachyonic instabilities and high-energy ghosts to gradient instabilities, with rare cases where interactions stabilize two ghosts.
Jeans' Ghost
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abstract
We show that a massless canonical scalar field minimally coupled to general relativity can become a tachyonic ghost at low energies around a background in which the scalar's gradient is spacelike. By performing a canonical transformation we demonstrate that this low energy ghost can be recast, at the level of the action, in a form of a fluid that undergoes a Jeans-like instability affecting only modes with large wavelength. This illustrates that low-energy tachyonic ghosts do not lead to a catastrophic quantum vacuum instability, unlike the usual high-energy ghost degrees of freedom.
fields
gr-qc 1years
2019 1verdicts
CONDITIONAL 1representative citing papers
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Cosmological Instabilities and the Role of Matter Interactions in Dynamical Dark Energy Models
For two interacting scalar fields, low-energy ghosts are equivalent to tachyonic instabilities and high-energy ghosts to gradient instabilities, with rare cases where interactions stabilize two ghosts.