Genus Statistics of the Large-Scale Structure with Non-Gaussian Density Fields

As a statistical measure to quantify the topological structure of the large-scale structure in the universe, the genus number is calculated for a number of non-Gaussian distributions in which the density field is characterized by a nontrivial function of some Gaussian-distributed random numbers. As a specific example, the formulae for the lognormal and the chi-square distributions are derived and compared with the results of $N$-body simulations together with the previously known formulae for the Gaussian distribution and second-order perturbation theory. It is shown that the lognormal formula fits most of the simulation data the best.