Abstract
Abstract
We construct explicit models of classical primordial standard clocks in an alternative to
inflation, namely the slowly contracting ekpyrotic scenario. We study the phenomenology of massive
spectator fields added to a state-of-the-art ekpyrotic model, with coupling functions that allow
for these heavy fields to be classically excited while the background is slowly contracting. We
perform numerical computations of the corrections to the scalar primordial power spectrum and
compare with analytical estimates. Our full numerical results reveal so-called clock signals,
sharp feature signals, as well as signals that link the two together. The models are found to
predict oscillatory features that are resolutely different from what is calculated in inflation,
and thus, such features represent unique fingerprints of a slowly contracting universe. This
confirms the capability of primordial standard clocks to model-independently discriminate among
very early universe scenarios.