Abstract
Interpreting observations of the Lyman-$\alpha$ forest flux power spectrum
requires interpolation between a small number of expensive simulations. We
present a Gaussian process emulator modelling the 1D flux power spectrum as a
function of the amplitude and slope of the small-scale linear matter power
spectrum, and the state of the intergalactic medium at the epoch of interest
($2 < z < 4$). This parameterisation enables the prediction of the flux power
spectrum in extended cosmological models that are not explicitly included in
the training set, eliminating the need to construct bespoke emulators for a
number of extensions to $Łambda$CDM. We demonstrate this for massive neutrino
cosmologies, where the emulator is able to predict the flux power spectrum in a
$\Sigma m_\nu=0.3$ eV neutrino cosmology to sub-percent accuracy, without
including massive neutrinos in the training simulations. This work will
facilitate the combination of upcoming data from the Dark Energy Spectroscopic
Instrument with observations of the cosmic microwave background, to obtain
constraints on neutrino mass and other extensions to $Łambda$CDM cosmology.
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