Towards an accurate model of small-scale redshift-space distortions in
  modified gravity
  The coming generation of galaxy surveys will provide measurements of galaxy
clustering with unprecedented accuracy and data size, which will allow us to
test cosmological models at much higher precision than achievable previously.
This means that we must have more accurate theoretical predictions to compare
with future observational data. As a first step towards more accurate modelling
of the redshift space distortions (RSD) of small-scale galaxy clustering in
modified gravity (MG) cosmologies, we investigate the validity of the so-called
Skew-T (ST) probability distribution function (PDF) of halo pairwise peculiar
velocities in these models. We show that, combined with the streaming model of
RSD, the ST PDF substantially improves the small-scale predictions by
incorporating skewness and kurtosis, for both $\Lambda$CDM and two leading MG
models: $f(R)$ gravity and the DGP braneworld model. The ST model reproduces
the velocity PDF and redshift-space halo clustering measured from MG $N$-body
simulations very well down to $\sim 5 \, h^{-1}\mathrm{Mpc}$. In particular, we
investigate the enhancements of halo pairwise velocity moments with respect to
$\Lambda$CDM for a larger range of MG variants than previous works, and present
simple explanations to the behaviours observed. By performing a simple Fisher
analysis, we find a significnat increase in constraining power to detect
modifications of General Relativity by introducing small-scale information in
the RSD analyses.
