A Non-Degenerate Neutrino Mass Signature in the Galaxy Bispectrum
  In the Standard Model, neutrinos are massless, yet oscillation experiments
show in fact they do have a small mass. Currently only the differences of the
masses' squares are known, and an upper bound on the sum. However, upcoming
surveys of the Universe's large-scale structure (LSS) can probe the neutrino
mass by exposing how neutrinos modulate galaxy clustering. But these
measurements are challenging: in looking at the clustering of galaxy pairs, the
effect of neutrinos is degenerate with galaxy formation, the details of which
are unknown. Marginalizing over them degrades the constraints. Here we show
that using correlations of galaxy triplets---the 3-Point Correlation Function
or its Fourier-space analog the bispectrum---can break the degeneracy between
galaxy formation physics (known as biasing) and the neutrino mass.
Specifically, we find a signature of neutrinos in the bispectrum's dipole
moment (with respect to triangle opening angle) that is roughly orthogonal to
the contribution of galaxy biases. This signature was missed in previous works
by failing to account for how neutrinos alter mode-coupling between
perturbations on different scales. Our proposed signature will contribute to
upcoming LSS surveys' such as DESI making a robust detection of the neutrino
mass. We estimate that it can offer several-$\sigma$ evidence for non-zero
$m_{\nu}$ with DESI from the bispectrum alone, and that this is independent
from information in the galaxy power spectrum.
