Observing patchy reionization with future CMB polarization experiments
  We study the signal from patchy reionization in view of the future high
accuracy polarization measurements of the Cosmic Microwave Background (CMB). We
implement an extraction procedure of the patchy reionization signal analogous
to CMB lensing. We evaluate the signal to noise ratio (SNR) for the future
Stage IV (S4) CMB experiment. The signal has a broad peak centered on the
degree angular scales, with a long tail at higher multipoles. The CMB S4
experiment can effectively constrain the properties of reionization by
measuring the signal on degree scales. The signal amplitude depends on the
properties of the structure determining the reionization morphology. We
describe bubbles having radii distributed log-normally. The expected S/N is
sensitive to the mean bubble radius: $\bar{R}=5$ Mpc implies $S/N \approx 4$,
$\bar{R}=10$ Mpc implies $S/N \approx 20$. The spread of the radii distribution
strongly affects the integrated SNR, that changes by a factor of $10^2$ when
$\sigma_{lnr}$ goes from $\ln 2$ to $\ln3$. Future CMB experiments will thus
place important constraints on the physics of reionization.
