Effects of Massive Neutrinos on the Large-Scale Structure of the Universe

TL;DR

This study probes how massive neutrinos affect non-linear large-scale structure using grid-based hydrodynamical N-body simulations that include a neutrino fluid. It analyzes halo mass function, halo clustering with bias, and redshift-space distortions, contrasting $\Lambda$CDM and $\Lambda$CDM+$\nu$ cosmologies and testing against semi-analytic models like Sheth–Mo–Tormen. Key findings show neutrinos suppress high-mass halo counts but boost halo bias, leading to enhanced real-space halo clustering, while reducing bulk flows and velocity dispersions that shape RSD, with implications for interpreting $\beta$ and $\sigma_{12}$. Although there is a strong $M_\nu$–$\sigma_8$ degeneracy, measurements of $\beta$ in upcoming nearly all-sky surveys offer a viable path to constrain the total neutrino mass, particularly when combined with complementary probes.

Abstract

Cosmological neutrinos strongly affect the evolution of the largest structures in the Universe, i.e. galaxies and galaxy clusters. We use large box-size full hydrodynamic simulations to investigate the non-linear effects that massive neutrinos have on the spatial properties of cold dark matter (CDM) haloes. We quantify the difference with respect to the concordance LambdaCDM model of the halo mass function and of the halo two-point correlation function. We model the redshift-space distortions and compute the errors on the linear distortion parameter beta introduced if cosmological neutrinos are assumed to be massless. We find that, if not taken correctly into account and depending on the total neutrino mass, these effects could lead to a potentially fake signature of modified gravity. Future nearly all-sky spectroscopic galaxy surveys will be able to constrain the neutrino mass if it is larger than 0.6 eV, using beta measurements alone and independently of the value of the matter power spectrum normalisation. In combination with other cosmological probes, this will strengthen neutrino mass constraints and help breaking parameter degeneracies.

Figures (8)

• Figure 1: DM halo MF as a function of $M_\nu$ and redshift. Left: MF of the SUBFIND haloes in the $\Lambda$CDM N-body simulation (blue circles) and in the two simulations with $M_\nu=0.3$ eV (magenta triangles) and $M_\nu=0.6$ eV (red squares). The blue, magenta and red lines show the halo MF predicted by sheth2002, where the variance in the density fluctuation field, $\sigma(M)$, for the three cases, $M_\nu=0,0.3,0.6$ eV, has been computed using the linear matter $P(k)$ extracted from CAMB. Right: ratio between the halo MFs of the simulations with and without neutrinos. The green triangles show the MF ratios of the FoF haloes, while yellow circles show the ones of the SUBFIND haloes. The lines represent the ST-MF ratios: the black solid lines are the MF ratios predicted for $M_\nu=0.3$ eV and $M_\nu=0.6$ eV; the red dashed lines are the same ratios but assuming $\bar{\rho}=\rho_{c}\cdot(\Omega_m-\Omega_\nu)$ in the ST-MF formula Eq. (\ref{['eq:MF']}) brandbyge2010; finally, the blue dotted lines are the ratios between the ST MFs in two $\Lambda$CDM cosmologies, which differ for the $\sigma_8$ normalisation, as explained in the text. The error bars represent the statistical Poisson noise.
• Figure 2: Real-space two-point auto-correlation function of the DM haloes in the $\Lambda$CDM N-body simulation (blue circles) and in the simulation with $M_\nu=0.6$ eV (red squares). The blue and red lines show the DM correlation function, for $M_\nu=0$ and $M_\nu=0.6$ eV, respectively, obtained by Fourier trasforming the non-linear power spectrum extracted from CAMB lewis2002 which exploits the HALOFIT routine smith2003. The bottom panels show the ratio between the halo correlation function of the simulations with and without neutrinos. The error bars represent the statistical Poisson noise corrected at large scales as prescribed by mo1992.
• Figure 3: DM halo bias, $b=(\xi_{\rm halo}/\xi_{\rm DM})^{0.5}$, measured from the $\Lambda$CDM simulations (blue circles) and from the two simulations with $M_\nu=0.3$ eV (magenta triangles) and $M_\nu=0.6$ eV (red squares). The error bars represent the propagated Poisson noise corrected at large scales as prescribed by mo1992. Dotted lines are the theoretical predictions of sheth_mo_tormen2001 (Eq. (\ref{['eq:bias']})). The four panels show the results at different redshifts, as labeled.
• Figure 4: Mean bias (averaged in $10\,h^{-1}\,\hbox{Mpc}<r<50\,h^{-1}\,\hbox{Mpc}$) as a function of redshift compared to the theoretical predictions of sheth_mo_tormen2001 (dotted lines) (Eq. (\ref{['eq:bias']})). Here the dashed lines represent the theoretical expectations for a $\Lambda$CDM cosmology renormalized with the $\sigma_8$ value of the simulations with a massive neutrino component. The error bars represent the propagated Poisson noise corrected at large scales as prescribed by mo1992.
• Figure 5: Two-point auto-correlation function in real and redshift space of the DM haloes in the $\Lambda$CDM N-body simulation (blue circles) and in the simulation with $M_\nu=0.6$ eV (red squares). The bottom panels show the ratio between them, compared with the theoretical expectation given by Eq. (\ref{['eq:xiratio']}). The error bars represent the statistical Poisson noise corrected at large scales as prescribed by mo1992.