## Abstract

We present a phenomenological modification of the standard perturbation theory prediction for the bispectrum in redshift space that allows us to extend the model to mildly non-linear scales over a wide range of redshifts, z ≤ 1.5. Our model require 18 free parameters that are fitted to N-body simulations using the shapes k_{2}/k_{1} = 1, 1.5, 2.0, 2.5. We find that we can describe the bispectrum of dark matter particles with ∼ 5% accuracy for k_{i} ≲ 0.10h/Mpc at z = 0, for k_{i} ≲ 0.15h/Mpc at z = 0.5, for k_{i} ≲ 0.17h/Mpc at z = 1.0 and for k_{i} ≲ 0.20h/Mpc at z = 1.5. For very squeezed triangles with k_{1} = k_{2} ≳ 0.1 hMpc^{-1} and k3 ≤ 0.02 hMpc^{-1}, however, neither SPT nor the proposed fitting formula are able to describe the measured dark matter bispectrum with this accuracy. We show that the fitting formula is sufficiently general that can be applied to other intermediate shapes such as k_{2}/k_{1} = 1.25, 1.75, and 2.25. We also test that the fitting formula is able to describe with similar accuracy the bispectrum of cosmologies with different Ω_{m}, in the range 0.2 ≲ Ω_{m} ≲ 0.4, and consequently with different values of the logarithmic grow rate f at z = 0, 0.4 ≲ f(z = 0) ≲ 0.6. We apply this new formula to recover the bias parameters, f and σ_{8}, by combining the redshift space power spectrum monopole and quadrupole with the bispectrum monopole for both dark matter particles and haloes. We find that the combination of these three statistics can break the degeneracy between b_{1}, f and σ_{s}. For dark matter particles the new model can be used to recover f and σ_{s} with ∼ 1% accuracy. For dark matter haloes we find that f and σ_{s} present larger systematic shifts, ∼ 10%. The systematic offsets arise because of limitations in the modelling of the interplay between bias and redshift space distortions, and represent a limitation as the statistical errors of forthcoming surveys reach this level. Conveniently, we find that these residual systematics are mitigated for combinations of parameters. In particular, the quantity fσ_{s} is still recovered with ∼ 1% accuracy for the particular halo population and cosmology studied. The improvement on the modelling of the bispectrum presented in this paper will be useful for extracting information from current and future galaxy surveys.

Original language | English |
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Article number | 29 |

Journal | Journal of Cosmology and Astroparticle Physics |

Volume | 2014 |

Issue number | 12 |

DOIs | |

State | Published - 2014 |

Externally published | Yes |

## Keywords

- Cosmological parameters from LSS
- Cosmological simulations
- Power spectrum