Effects of neutrino masses and asymmetries on dark matter halo assembly

Massive cosmological neutrinos suppress the Large-Scale Structure (LSS) in the Universe by smoothing the cosmic over-densities, and hence structure formation is delayed relative to that in the standard Lambda-Cold Dark Matter (ACDM) model. We characterize the merger and mass accretion history of dark matter halos with the halo formation time a(1/2), tree entropy s and halo leaf function l(X) and measure them using neutrino-involved N-body simulations. We show that a non-zero sum of neutrino masses M-nu delays the a(1/2) for halos with virial mass between 10(13) M-circle dot and 3 x 10(13) M-circle dot, whereas a non-zero neutrino asymmetry parameter eta(2) has the opposite effect. While the mean tree entropy (s) over bar does not depend significantly on either M-nu or eta(2), the halo leaf function does. Furthermore, the dependencies of on M-nu and eta(2) have significant evolution in redshift z, with the relative contributions of M-nu and eta(2) showing a sigmoid-like transition as a function of z around z approximate to 0.6. Together with the matter power spectrum, these halo parameters allow us to break the parameter degeneracy between M-nu and eta(2) so that they can both be constrained in principle.

Automated summary

Massive cosmological neutrinos can smooth the large-scale structure in the universe and delay structure formation. N-body simulations involving neutrinos are used to measure the merger and mass accretion history of dark matter halos. It is found that non-zero neutrino masses delay the formation of halos within a certain range of virial mass, while non-zero neutrino asymmetry parameter has the opposite effect. The dependencies of these parameters also evolve with redshift.