Gauging the Reaction: A new framework for non-linear clustering in ΛCDM and beyond

The high-quality data produced by upcoming weak lensing surveys will require percent-level knowledge of the matter power spectrum down to small and information-rich non-linear scales. Due to their intrinsic inaccuracies in this regime, computationally efficient approaches routinely used nowadays, such as semi-analytical methods and fitting functions, will be inadequate for future cosmological analyses. Interesting progress has been made in the last decade with the help of machine learning and the advent of matter power spectrum emulators. However, these predictive tools rely heavily on cosmological N-body simulations, requiring extremely massive computing resources to cover a significant fraction of the theory landscape. In this talk I will present the halo model reaction framework as a possible solution to these shortcomings, in which a combination of perturbation theory, halo model and emulators is used to swiftly and accurately predict the non-linear matter power spectrum in the standard cosmology and its extensions. I will show the performance of this method for well-known modifications of gravity, dark energy parametrizations and massive neutrinos, as well as the deep connection emerging between halo properties and matter power spectrum.