  Massive particles leave imprints on primordial non-Gaussianity via couplings
to the inflaton, even despite their exponential dilution during inflation:
practically, the Universe acts as a Cosmological Collider. We present the first
dedicated search for spin-zero particles using BOSS redshift-space galaxy power
spectrum and bispectrum multipoles, as well as Planck CMB non-Gaussianity data.
We demonstrate that some Cosmological Collider models are well approximated by
the standard equilateral and orthogonal parametrization; assuming negligible
inflaton self-interactions, this facilitates us translating Planck
non-Gaussianity constraints into bounds on Collider models. Many models have
signatures that are not degenerate with equilateral and orthogonal
non-Gaussianity and thus require dedicated searches. Here, we constrain such
models using BOSS three-dimensional redshift-space galaxy clustering data,
focusing on spin-zero particles in the principal series and constraining their
couplings to the inflaton at varying speed and mass, marginalizing over the
unknown inflaton self-interactions. This is made possible through an
improvement in Cosmological Bootstrap techniques and the combination of
perturbation theory and halo occupation distribution models for galaxy
clustering. Our work sets the standard for inflationary spectroscopy with
cosmological observations, providing the ultimate link between physics on the
largest and smallest scales.
