The dipole of the galaxy bispectrum
  The bispectrum will play an important role in future galaxy surveys. On large
scales it is a key probe for measuring primordial non-Gaussianity which can
help differentiate between different inflationary models and other theories of
the early universe. On these scales a variety of relativistic effects come into
play once the galaxy number-count fluctuation is projected onto our past
lightcone. We show for the first time that the leading relativistic correction
from these distortions in the galaxy bispectrum generates a significant dipole,
mainly from relativistic redshift space distortions. The amplitude of the
dipole can be more than 10% of the monopole even on equality scales. Such a
dipole is absent in the Newtonian approximation to the redshift space
bispectrum, so it offers a clear signature of relativistic effects on
cosmological scales in large scale structure.
