Constraining the Neutrino Mass with the Drifting Coefficient of the Field Cluster Mass Function

A new diagnostics to break the degeneracy between the total neutrino mass ($M_{\nu}$) and the primordial power spectrum amplitude ($\sigma_{8}$) by using the drifting coefficient of the field cluster mass function is presented. Analyzing the data from the Cosmological Massive Neutrino Simulations, we first determine the numerical mass functions of the field clusters at various redshifts. Then, we compare the numerical results with the analytical model characterized by a single parameter called the drifting coefficient which measures the drifts of the collapse density threshold, $\delta_{c}$, from the Einstein-de Sitter spherical value, $\delta_{sc}$, at a given mass scale. It is found that the analytic model for the field cluster mass function is found to work excellently even in the presence of massive neutrinos and that its drifting coefficient evolves differently in the cosmologies with different values of $M_{\nu}$. At low redshifts ($z\lesssim 0.3$) the more massive neutrinos drift $\delta_{c}$ further from $\delta_{sc}$, while the opposite trend is found at higher redshifts ($z\gtrsim0.3$). Speculating that this distinct redshift-dependent effect of massive neutrinos on the drifting coefficient of the field cluster mass function might help break the $\sigma_{8}$-$M_{\nu}$ degeneracy, we also show that the sensitivity of this new diagnostics to $M_{\nu}$ is high enough to discriminate the case of $M_{\nu}=0.1\,{\rm eV}$ from that of massless neutrinos.