Anisotropic separate universe simulations

The long-wavelength coherent overdensity and tidal force, which are not direct observables for a finite-volume survey, affect time evolution of cosmic structure formation and therefore clustering observables through the mode coupling. In this paper, we develop an 'anisotropic' separate universe (SU) simulation technique to simulate large-scale structure formation taking into account the effect of large-scale tidal force into the anisotropic expansion of local background. We modify the TREEPM N-body simulation code to implement the anisotropic SU simulations, and then study the 'response' function of matter power spectrum that describes how the matter power spectrum responds to the large-scale tidal effect as a function of wavenumber and redshift for a given global cosmology. We test and validate the SU simulation results from the comparison with the perturbation theory predictions and the results from high-resolution particle-mesh simulations. We find that the response function displays characteristic scale dependencies over the range of scales down to non-linear scales, up to k similar or equal to 6h Mpc(-1).