Constraining Planck scale physics with CMB and Reionization Optical
  Depth
  We present proof of principle for a two way interplay between physics at very
early Universe and late time observations. We find a relation between
primordial mechanisms responsible for large scale power suppression in the
primordial power spectrum and the value of reionization optical depth $\tau$.
Such mechanisms can affect the estimation of $\tau$. We show that using future
measurements of $\tau$, one can obtain constraints on the pre-inflationary
dynamics, providing a new window on the physics of the very early Universe.
Furthermore, the new, re-estimated $\tau$ can potentially resolve moderate
discrepancy between high and low-$\ell$ measurements of $\tau$, hence providing
empirical support for the power suppression anomaly and its primordial origin.
