The Lyman-alpha forest in f(R) modified gravity
  In this work, we analyze the Lyman-$\alpha$ forest in cosmological
hydrodynamical simulations of chameleon-type f(R) gravity with the goal to
assess whether the impact of such models is detectable in absorption line
statistics. We carry out a set of hydrodynamical simulations with the
cosmological simulation code MG-GADGET, including star formation and cooling
effects, and create synthetic Lyman-$\alpha$ absorption spectra from the
simulation outputs. We statistically compare simulations with f(R) and ordinary
general relativity, focusing on flux probability distribution functions (PDFs)
and flux power-spectra, an analysis of the column density and line width
distributions, as well as the matter power spectrum. We find that the influence
of f(R) gravity on the Lyman-$\alpha$ forest is rather small. Even models with
strong modifications of gravity, like $|\bar{f}_{R0}| = 10^{-4}$, do not change
the statistical Lyman-$\alpha$ properties by more than 10%. The column density
and line width distributions are hardly affected at all. It is therefore not
possible to get competitive constraints on the background field $f_R$ using
current observational data. An improved understanding of systematics in the
observations and a more accurate modeling of the baryonic/radiative physics
would be required to allow this in the future. The impact of f(R) on the matter
power spectrum in our results is consistent with previous works.
