Non-linear dark energy clustering
  We consider a dark energy fluid with arbitrary sound speed and equation of
state and discuss the effect of its clustering on the cold dark matter
distribution at the non-linear level. We write the continuity, Euler and
Poisson equations for the system in the Newtonian approximation. Then, using
the time renormalization group method to resum perturbative corrections at all
orders, we compute the total clustering power spectrum and matter power
spectrum. At the linear level, a sound speed of dark energy different from that
of light modifies the power spectrum on observationally interesting scales,
such as those relevant for baryonic acoustic oscillations. We show that the
effect of varying the sound speed of dark energy on the non-linear corrections
to the matter power spectrum is below the per cent level, and therefore these
corrections can be well modelled by their counterpart in cosmological scenarios
with smooth dark energy. We also show that the non-linear effects on the matter
growth index can be as large as 10-15 per cent for small scales.
