Hosted by: Anze Slosar

Understanding structure formation is one of the most important issues in modern cosmology. In particular, in the era of big astronomical data, connecting observation and theory is crucial to improve precision cosmology, and possibly probe new physics. The observables of large-scale structure, such as galaxy number density, generally depend on the density of the environment. This dependence can traditionally be studied by performing gigantic cosmological N-body simulations and measuring the observables in different density environments. Alternatively, we can perform so-called ``separate universe simulations,'' in which the effect of the environment is absorbed into the change of the cosmological parameters. In other words, an overdense universe is equivalent to a positively curved universe, and the structure formation would change accordingly. In this talk, I will introduce the separate universe mapping, and present how the power spectrum and halo mass function changes in different density environments, which are related to the squeezed-limit bispectrum and the halo bias, respectively. I will also discuss our recent progress on extending this approach to multiple fluids such as dynamic dark energy and massive neutrinos.