On the road to percent accuracy II: calibration of the non-linear matter power spectrum for arbitrary cosmologies

We introduce an emulator approach to predict the non-linear matter power spectrum for broad classes of beyond-Lambda CDM cosmologies, using only a suite of Lambda CDM N-body simulations. By including a range of suitably modified initial conditions in the simulations, and rescaling the resulting emulator predictions with analytical 'halo model reactions', accurate non-linear matter power spectra for general extensions to the standard Lambda CDM model can be calculated. We optimize the emulator design by substituting the simulation suite with non-linear predictions from the standard HALOFIT tool. We review the performance of the emulator for artificially generated departures from the standard cosmology as well as for theoretically motivated models, such as f(R) gravity and massive neutrinos. For the majority of cosmologies we have tested, the emulator can reproduce the matter power spectrum with errors less than or similar to 1 per cent deep into the highly non-linear regime. This work demonstrates that with a well-designed suite of Lambda CDM simulations, extensions to the standard cosmological model can be tested in the non-linear regime without any reliance on expensive beyond-Lambda CDM simulations.