  Massive particles produced during inflation leave specific signatures in soft
limits of correlation functions of primordial fluctuations. When the Goldstone
boson of broken time translations acquires a reduced speed of sound, implying
that de Sitter boosts are strongly broken, we introduce a novel discovery
channel to detect new physics during inflation, called the cosmological
low-speed collider signal. This signal is characterised by a distinctive
resonance lying in mildly-soft kinematic configurations of cosmological
correlators, indicating the presence of a heavy particle, whose position
enables to reconstruct its mass. We show that this resonance can be understood
in terms of a non-local single field effective field theory, in which the heavy
field becomes effectively non-dynamical. This theory accurately describes the
full dynamics of the Goldstone boson and captures all multi-field physical
effects distinct from the non-perturbative particle production leading to the
conventional cosmological collider signal. As such, this theory provides a
systematic and tractable way to study the imprint of massive fields on
cosmological correlators. We conduct a thorough study of the low-speed collider
phenomenology in the scalar bispectrum, showing that large non-Gaussianities
with new shapes can be generated, in particular beyond weak mixing. We also
provide a low-speed collider template for future cosmological surveys.
