We present GEO-FPT (Geometric Fitted Perturbation Theory), a new model for
the galaxy bispectrum anisotropic signal in redshift space, with functional
form rooted in perturbation theory. It also models the dependence of the
bispectrum with the geometric properties of the triangles in Fourier space, and
has a broader regime of validity than state-of-the-art theoretical models based
on perturbation theory. We calibrate the free parameters of this model using
high-resolution dark matter simulations and perform stringent tests to show
that GEO-FPT describes the galaxy bispectrum accurately up to scales of
k≃0.12hMpc−1 for different cosmological models, as well as for
biased tracers of the dark matter field, considering a survey volume of 100
(Gpc h−1)3. In particular, a joint analysis of the power spectrum and
bispectrum anisotropic signals, taking into account their full covariance
matrix, reveals that the relevant physical quantities -- the BAO peak position
(along and across the line-of-sight), and the growth of structure parameters
times the amplitude of dark matter fluctuations, fσ8-- are recovered in
an unbiased way, with an accuracy better than 0.4% and 2% respectively
(which is our 2σ statistical limit of the systematic error estimate). In
addition, the bispectrum signal breaks the fσ8 degeneracy without
detectable bias: f and σ8 are recovered with better than 2.7% and
3.8% accuracy respectively (which is our 2σ statistical limit of the
systematic error estimate).
GEO-FPT boosts the applicability of the bispectrum signal of galaxy surveys
beyond the current limitation of k≲0.08h Mpc−1 % and makes the
bispectrum a key statistic to unlock the information content from the mildly
non-linear regime in the on-going and forthcoming galaxy redshift surveys.Comment: 37 pages, 14 figures. To be submitted to JCAP, comments welcom