  Upcoming large-scale structure surveys will measure the matter power spectrum
to approximately percent level accuracy with the aim of searching for evidence
for new physics beyond the standard model of cosmology. In order to avoid
biasing our conclusions, the theoretical predictions need to be at least as
accurate as the measurements for a given choice of cosmological parameters.
However, recent theoretical work has shown that complex physical processes
associated with galaxy formation (particularly energetic feedback processes
associated with stars and especially supermassive black holes) can alter the
predictions by many times larger than the required accuracy. Here we present
$\texttt{SP(k)}$, a model for the effects of baryon physics on the non-linear
matter power spectrum based on a new large suite of hydrodynamical simulations.
Specifically, the ANTILLES suite consists of 400 simulations spanning a very
wide range of the "feedback landscape" and show that the effects of baryons on
the matter power spectrum can be understood at approaching the percent level in
terms of the mean baryon fraction of haloes, at scales of up to $k \lesssim 10
\, h \, $Mpc$^{-1}$ and redshifts up to $z=3$. For the range of scales and
redshifts that will be probed by forthcoming cosmic shear measurements, most of
the effects are driven by galaxy group-mass haloes ($M \sim 10^{13-14}$
M$_\odot$). We present a simple Python implementation of our model, available
at
$\href{https://github.com/jemme07/pyspk}{\mathrm{https{:}//github.com/jemme07/pyspk}}$,
which can be used to incorporate baryon effects in standard gravity-only
predictions, allowing for marginalisation over baryon physics within
cosmological pipelines.
