Paper detail

Particle production during Inflation with a non-minimally coupled spectator scalar field

We study the inflationary model with a spectator scalar field $χ$ coupled to both the inflaton and Ricci scalar. The interaction between the $χ$ field and the gravity, denoted by $ξRχ^2$, can trigger the tachyonic instability of certain modes of the $χ$ field. As a result, the $χ$ field perturbations are amplified and serve as a gravitational wave (GW) source. When considering the backreaction of the $χ$ field, an upper bound on the coupling parameter $ξ$ must be imposed to ensure that inflation does not end prematurely. In this case, we find that the inflaton's evolution experiences a sudden slowdown due to the production of $χ$ particles, resulting in a unique oscillating structure in the power spectrum of curvature perturbations at specific scales. Moreover, the GW signal induced by the $χ$ field is more significant than primordial GWs at around its peak scale, leading to a noticeable bump in the overall energy spectrum of GWs. It's worth noting that this bump predicted in the slow-roll inflationary scenario is unlikely to be detected by LISA and Taiji, but there is a slim chance it might approach the detection limits of GW experiments like BBO and SKA if we devise distinctive inflatonary potentials.