Building Mock Galaxy Catalogues to Test the Nature of Gravity

The Theory of General Relativity (GR) is very well-tested on local Solar System scales, but tests on the largest cosmological scales have been limited by the volume and precision of existing galaxy surveys. This situation is expected to change in the
coming decade with the advent of several new spectroscopic redshift surveys like desi and Euclid. In this project, we test the nature of gravity on these scales by using cosmological simulations to construct mock galaxy catalogs that mimic surveys as closely
as possible. In particular, we focus on ΛCDM and three variants of the f(R) model of modified gravity: F6, F5, F4, each of which enhance the strength of gravity relative to GR with increasing intensity. Because of the inherent nonlinearity of the f(R)
model, we use large-scale numerical simulations that self-consistently evolve dark matter particles according to these modified equations of motion. In computing the two-point 3D real-space correlation function of the resulting dark matter halos, we find that due to differences in the intensity of the enhancement of gravity, dark matter halos in F4 are significantly less clustered than GR, F6 is slightly less clustered, and F5 is slightly more clustered. We transform each of these halo catalogues using the Halo Occupation
Distribution model, which determines the likelihood of a halo having a certain number of galaxies based upon its mass. Finally, we trim these galaxy catalogues even further by applying survey realism, ensuring that the galaxy distribution in the two cosmologies is
identical to the observer.