On the Nonspherical Nature of Halo Formation

We present a new collapse condition to describe the formation of dark halosvia nonspherical gravitational clustering. This new nonspherical collapsecondition is obtained by the logical generalization of the spherical model tothe nonspherical one. By solving a diffusion-like random matrix equation withthe help of the Monte Carlo method, we show that this nonspherical collapsecondition yields the mass function derived by Sheth & Tormen (1999) which hasbeen shown to be in excellent agreement with the recent N-body results of highresolution. We expect that this nonspherical collapse condition might provideus a deeper insight into the structure formation, and suggest that it should bewidely applied to various cosmological issues such as the galaxy merginghistory, the galaxy bias, and so forth.Comment: Accepted version, ApJ in press, LaTex file, 1 ps figure, mistakes and typos correcte