CMB Bispectrum from Non-linear Effects during Recombination

Understand

We study cosmological perturbations by solving the governing Boltzmann and Einstein Field equations up to second order, and calculate the corresponding CMB bispectrum during recombination.

• We include all the second-order Liouville and collision terms, truncating the multipole hierarchy at $l=10$, consistently including all $m\neq 0$ terms when calculating the bispectrum in the flat-sky limit.
• At this stage, we focus on contributions at recombination and we neglect 2nd-order vector and tensor terms, lensing effects, and late time non-linear ISW.
• We find that the signal-to-noise for the bispectrum is 0.69 for $l_{max}=2000$, yielding an overall signal $F_{\rm NL} = 3.19$ (normalised relative to the local model).