Primordial gravitational waves from excited states

@article{Fumagalli2022PrimordialGW,
  title={Primordial gravitational waves from excited states},
  author={Jacopo Fumagalli and Gonzalo A. Palma and S'ebastien Renaux-Petel and Spyros Sypsas and Lukas T. Witkowski and Cristobal Zenteno},
  journal={Journal of High Energy Physics},
  year={2022},
  volume={2022},
  pages={1-55}
}
We show that a scalar excited state with large occupation numbers during inflation leads to an enhancement of tensor modes and a characteristic pattern of order-one oscillations in the associated stochastic gravitational wave background (SGWB) sourced during inflation. An effective excited state, i.e. a departure from the Bunch-Davies vacuum, can emerge dynamically as the result of a transient non-adiabatic evolution, e.g. a sharp feature along the inflationary history. We provide an explicit… 
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