The cosmological collider signal in the non-BD initial states

Abstract

We investigate the cosmological collider (CC) signal arising from the tree-level exchange of a scalar spectator particle with a non-Bunch Davies (BD) initial state. We decompose the inflaton correlators into seed integrals, which we compute analytically by solving the bootstrap equations. We show that the non-BD initial state eliminates the Hubble scale Boltzmann suppression $e^{-\pi m/H}$ that usually affects the CC signal. Consequently, in this scenario, the CC can probe an energy scale much higher than the inflationary Hubble scale $H$.