Detecting Electron Density Fluctuations from Cosmic Microwave Background
  Polarization using a Bispectrum Approach
  Recent progress in high sensitivity Cosmic Microwave Background (CMB)
polarization experiments opens up a window on large scale structure (LSS), as
CMB polarization fluctuations on small angular scales can arise from a
combination of LSS and ionization fluctuations in the late universe.
Gravitational lensing effects can be extracted from CMB datasets with quadratic
estimators but reconstructions of electron density fluctuations (EDFs) with
quadratic estimators are found to be significantly biased by the much larger
lensing effects in the secondary CMB fluctuations. In this paper we establish a
bispectrum formalism using tracers of LSS to extract the subdominant EDFs from
CMB polarization data. We find that this bispectrum can effectively reconstruct
angular band-powers of cross correlation between EDFs and LSS tracers. Next
generation CMB polarization experiments in conjunction with galaxy surveys and
cosmic infrared background experiments can detect signatures of EDFs with high
significance.
