A new scale in the bias expansion
  The fact that the spatial nonlocality of galaxy formation is controlled by
some short length scale like the Lagrangian radius is the cornerstone of the
bias expansion for large-scale-structure tracers. However, the first sources of
ionizing radiation between $z\approx 15$ and $z\approx 6$ are expected to have
significant effects on the formation of galaxies we observe at lower redshift,
at least on low-mass galaxies. These radiative-transfer effects introduce a new
scale in the clustering of galaxies, i.e. the finite distance which ionizing
radiation travels until it reaches a given galaxy. This mean free path can be
very large, of order $100\,h^{-1}\,{\rm Mpc}$. Consequently, higher-derivative
terms in the bias expansion could turn out to be non-negligible even on these
scales: treating them perturbatively would lead to a massive loss in
predictivity and, for example, could spoil the determination of the BAO feature
or constraints on the neutrino mass. Here, we investigate under what
assumptions an explicit non-perturbative model of radiative-transfer effects
can maintain the robustness of large-scale galaxy clustering as a cosmological
probe.
