What it Takes to Measure Reionization with Fast Radio Bursts
  Fast Radio Bursts (FRBs) are recently-discovered extra-galactic radio
transients which exhibit a distance-dependent dispersion of their signal, and
thus can be used as cosmological probes. In this article we, for the first
time, apply a model-independent approach to measure reionization from synthetic
FRB data assuming these signals are detected beyond redshift 5. This method
allows us to constrain the full shape of the reionization history as well as
the CMB optical depth $\tau$ while avoiding the pitfalls of commonly used
model-based techniques. Already 100 localized FRBs, originating from redshifts
z>5, could constrain (at 68% confidence level) the CMB optical depth to within
11%, and the midpoint of reionization to 4%, surpassing current
state-of-the-art CMB bounds and quasar limits. Owing to the higher numbers of
expected FRBs at lower redshifts, the $\tau$ constraints are asymmetric (+14%,
-7%) providing a much stronger lower limit. Finally, we show that the
independent constraints on reionization from FRBs will improve limits on other
cosmological parameters such as the amplitude of the power spectrum of
primordial fluctuations.
