Galaxy Bispectrum from Massive Spinning Particles
  Massive spinning particles, if present during inflation, lead to a
distinctive bispectrum of primordial perturbations, the shape and amplitude of
which depend on the masses and spins of the extra particles. This signal, in
turn, leaves an imprint in the statistical distribution of galaxies; in
particular, as a non-vanishing galaxy bispectrum, which can be used to probe
the masses and spins of these particles. In this paper, we present for the
first time a new theoretical template for the bispectrum generated by massive
spinning particles, valid for a general triangle configuration. We then proceed
to perform a Fisher-matrix forecast to assess the potential of two
next-generation spectroscopic galaxy surveys, EUCLID and DESI, to constrain the
primordial non-Gaussianity sourced by these extra particles. We model the
galaxy bispectrum using tree-level perturbation theory, accounting for
redshift-space distortions and the Alcock-Paczynski effect, and forecast
constraints on the primordial non-Gaussianity parameters marginalizing over all
relevant biases and cosmological parameters. Our results suggest that these
surveys would potentially be sensitive to any primordial non-Gaussianity with
an amplitude larger than $f_{\rm NL}\approx 1$, for massive particles with
spins 2, 3, and 4. Interestingly, if non-Gaussianities are present at that
level, these surveys will be able to infer the masses of these spinning
particles to within tens of percent. If detected, this would provide a very
clear window into the particle content of our Universe during inflation.
