The Linear Perturbation Theory of Reionization in Position-Space:
  Cosmological Radiative Transfer Along the Light-Cone
  The linear perturbation theory of inhomogeneous reionization (LPTR) has been
developed as an analytical tool for predicting the global ionized fraction and
large-scale power spectrum of ionized density fluctuations during reionization.
In the original formulation of the LPTR, the ionization balance and radiative
transfer equations are linearized and solved in Fourier space. However, the
LPTR's approximation to the full solution of the radiative transfer equation is
not straightforward to interpret, since the latter is most intuitively
conceptualized in position space. To bridge the gap between the LPTR and the
language of numerical radiative transfer, we present a new, equivalent,
position-space formulation of the LPTR that clarifies the approximations it
makes and facilitates its interpretation. We offer a comparison between the
LPTR and the excursion-set model of reionization (ESMR), and demonstrate the
built-in capability of the LPTR to explore a wide range of reionization
scenarios, and to go beyond the ESMR in exploring scenarios involving X-rays.
