Information Content of the Angular Multipoles of Redshift-Space Galaxy
  Bispectrum
  The redshift-space bispectrum (three point statistics) of galaxies depends on
the expansion rate, the growth rate, and geometry of the Universe, and hence
can be used to measure key cosmological parameters. In a homogeneous Universe
the bispectrum is a function of five variables and unlike its two point
statistics counterpart -- the power spectrum, which is a function of only two
variables -- is difficult to analyse unless the information is somehow reduced.
The most commonly considered reduction schemes rely on computing angular
integrals over possible orientations of the bispectrum triangle, thus reducing
it to sets of function of only three variables describing the triangle shape.
We use Fisher information formalism to study the information loss associated
with this angular integration. Without any reduction, the bispectrum alone can
deliver constraints on the growth rate parameter $f$ that are better by a
factor of $2.5$ compared to the power spectrum, for a sample of luminous red
galaxies expected from near future galaxy surveys at a redshift of $z\sim0.65$.
At lower redshifts the improvement could be up to a factor of $3$. We find that
most of the information is in the azimuthal averages of the first three even
multipoles. This suggests that the bispectrum of every configuration can be
reduced to just three numbers (instead of a 2D function) without significant
loss of cosmologically relevant information.
