An accurate halo model for fitting non-linear cosmological power spectra
  and baryonic feedback models
  We present an optimized variant of the halo model, designed to produce
accurate matter power spectra well into the non-linear regime for a wide range
of cosmological models. To do this, we introduce physically motivated free
parameters into the halo-model formalism and fit these to data from
high-resolution $N$-body simulations. For a variety of $\Lambda$CDM and $w$CDM
models the halo-model power is accurate to $\simeq 5$ per cent for $k\leq
10h\,\mathrm{Mpc}$ and $z\leq 2$. An advantage of our new halo model is that it
can be adapted to account for the effects of baryonic feedback on the power
spectrum. We demonstrate this by fitting the halo model to power spectra from
the OWLS hydrodynamical simulation suite via parameters that govern halo
internal structure. We are able to fit all feedback models investigated at the
5 per cent level using only two free parameters, and we place limits on the
range of these halo parameters for feedback models investigated by the OWLS
simulations. Accurate predictions to high-$k$ are vital for weak lensing
surveys, and these halo parameters could be considered nuisance parameters to
marginalize over in future analyses to mitigate uncertainty regarding the
details of feedback. Finally, we investigate how lensing observables predicted
by our model compare to those from simulations and from HALOFIT for a range of
$k$-cuts and feedback models and quantify the angular scales at which these
effects become important. Code to calculate power spectra from the model
presented in this paper can be found at
https://github.com/alexander-mead/hmcode
