Efficient Evaluation of Cosmological Angular Statistics
  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 $\ell$. 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.
