# DMWG Seminar by Dr. Nishimichi: Cosmology, the Fundamental for the DM on May 12, 2021

What we have known about dark matter (DM) is that it occupies ~25% of the energy density of our Universe. The precise determination of the cosmological parameter is crucially important for determining this abundance of DM. Another important point here is that one the value of those parameters are determined assuming a specific cosmological model, such as vanilla (i.e., the simplest) lambda CDM and so on. So we might have a different DM relic density if the assumption of the simplest Lambda-CDM breaks. Hence the examination of the cosmological parameters and the model behind them is important two-fold for DM physicists.

The basic observable for the cosmological parameter is cosmic microwave background, the large-scale structure, and so on. Those data are huge at the raw level, and still so large at the scientific data level. In order to derive a handful of cosmological parameters from such data, one must calculate the so-called summary statistics. By matching the summary statistics in simulation data of specific cosmological models (vanilla lambda-CDM, for example) adopting MCMC techniques, we arrive at the cosmological parameter that we need. Note that there is always degeneracy between cosmological parameters derived from observational data.

The matching between the observational and simulated summary statistics takes a lot of costs in the calculation. By adopting analytical formula, the calculation becomes much quicker while the precision decreases at some level. The emulator, which is developed in the Dark Quest Project, solves this computational problem. It enables us to speed up the calculation while keeping the precision. The degeneracy between the parameters also becomes accessible. The precise summary statistics such as halo mass function, halo-matter cross-correlation, and far more... is crucially important for DM study. Halo formation theory and weak lensing search are kinds of examples for applications.

With this new fantastic open-source tool of Dark Quest Project, the future for DM search study emerges definitely. We are looking forward to seeing a lot of cutting-edge as well as steady works implemented with this item in the near future!

Reported by Nagisa Hiroshima