Primordial gravitational waves from excited states

We show that a scalar excited state with large occupation numbers during inflation leads to an enhancement of tensor modes and characteristic pattern order-one oscillations in the associated stochastic gravitational wave background (SGWB) sourced inflation. An effective state, i.e. departure from Bunch-Davies vacuum, can emerge dynamically as result transient non-adiabatic evolution, e.g. sharp feature along inflationary history. provide explicit example multifield context where triggering is identified strong turn trajectory. En passant, we derive universal expression for power spectrum at second order by arbitrary number degrees freedom inflation, crucially taking into account nontrivial structure Hilbert space setups. The SGWB overcome standard scalar-induced horizon re-entry fluctuations after while being less constrained perturbativity backreaction bounds. In addition, one may entertain possibility detecting both since they peak different frequencies exhibiting distinct periods.