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arXiv · 2510.05204

Testing the arrow of time at the cosmo collider

Shuntaro Aoki·Alessandro Strumia
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Abstract

Normal particles carry a microscopic arrow of causality. Lee-Wick ghosts carry the reversed arrow, mediating characteristic collider signals in flat space: opposite-sign scattering amplitudes that violate positivity bounds; acausality on time scales set by their negative decay rate. During inflation, the corresponding cosmo-collider ghost signals are: opposite-sign non-Gaussianities; Boltzmann-unsuppressed local oscillatory signals without their non-local counterparts; IR-enhanced bi-spectrum and power spectrum, depending on the dimension of the interaction operator, which decreases if the ghost decay rate is comparable to the Hubble rate.

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Shuntaro Aoki, Alessandro Strumia. 2025-10-06. Testing the arrow of time at the cosmo collider. https://arxiv.org/abs/2510.05204

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