Angular statistics of cosmological observables are hard to compute. The main difficulty is due to the presence of highly-oscillatory Bessel functions which need to be integrated over. In this paper, we provide a simple and fast method to compute the angular power spectrum and bispectrum of any observable. The method is based on using an FFTlog algorithm to decompose the momentum-space statistics onto a basis of power-law functions. For each power law, the integrals over Bessel functions have a simple analytical solution. This allows us to efficiently evaluate these integrals, independently of the value of the multipole l. In particular, this method significantly speeds up the evaluation of the angular bispectrum compared to existing methods. To illustrate our algorithm, we compute the galaxy, lensing and CMB temperature angular power spectrum and bispectrum.
Journal of Cosmology and Astroparticle Physics
- Pub Date:
- November 2017
- Astrophysics - Cosmology and Nongalactic Astrophysics
- 31 pages, 10 figures, 2 tables. Added section on redshift space distortions. Added section on parameters and performances in appendix. Several minor modifications to match the published version in JCAP. (Title in published version changed)