Crinkles in the last scattering surface: Non-Gaussianity from inhomogeneous recombination

Understand

The perturbations in the electron number density during recombination contributes to the Cosmic Microwave Background bispectrum through second order terms.

• Perturbations in the electron density can be a factor of ~5 larger than the baryon density fluctuations on large scales as shown in the calculations by Novosyadlyj.
• This raises the possibility that the contribution to bispectrum arising from perturbations in the optical depth may be non-negligible.
• We calculate this bispectrum and find it to peak for squeezed triangles and of peak amplitude of the order of primordial non-Gaussianity of local type with fNL of 0.05 ~ -1 depending on the l-modes being considered.