Particle production in models with helicity-0 graviton ghost in de Sitter spacetime

Understand

We revisit the problem of the helicity-0 ghost mode of massive graviton in the de Sitter background.

• In general, the presence of a ghost particle, which has negative energy, drives the vacuum to be unstable through pair production of ghost particles and ordinary particles.
• In the case that the vacuum state preserves the de Sitter invariance, the number density created by the pair production inevitably diverges due to unsuppressed ultra-violet(UV) contributions.
• In such cases one can immediately conclude that the model is not viable.