Papers › Cosmic-Enu: An emulator for the non-linear neutrino power spectrum
Cosmic-Enu: An emulator for the non-linear neutrino power spectrum
Amol Upadhye, Juliana Kwan, Ian G. McCarthy, Jaime Salcido, Kelly R. Moran, Earl Lawrence, Yvonne Y. Y. Wong
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Cosmology is poised to measure the neutrino mass sum M_ν and has identified several smaller-scale observables sensitive to neutrinos, necessitating accurate predictions of neutrino clustering over a wide range of length scales. The FlowsForTheMasses non-linear perturbation theory for the massive neutrino power spectrum, Δ²_ν(k), agrees with its companion N-body simulation at the 10%-15% level for $k \leq 1~h/$Mpc. Building upon the Mira-Titan IV emulator for the cold matter, we use FlowsForTheMasses to construct an emulator for $\Delta^2_\nu(k)$ covering a large range of cosmological parameters and neutrino fractions $\Omega_{\nu,0} h^2 \leq 0.01$, which corresponds to M_ν ≤0.93~eV. Consistent with FlowsForTheMasses at the 3.5% level, it returns a power spectrum in milliseconds. Ranking the neutrinos by initial momenta, we also emulate the power spectra of momentum deciles, providing information about their perturbed distribution function. Comparing a M_ν=0.15~eV model to a wide range of N-body simulation methods, we find agreement to 3% for $k \leq 3 k_\mathrm{FS} = 0.17~h/$Mpc and to 19% for $k \leq 0.4~h/$Mpc. We find that the enhancement factor, the ratio of $\Delta^2_\nu(k)$ to its linear-response equivalent, is most strongly correlated with $\Omega_{\nu,0} h^2$, and also with the clustering amplitude σ₈. Furthermore, non-linearities enhance the free-streaming-limit scaling ∂log(Δ²_ν / Δ²ₘ) / ∂log(M_ν) beyond its linear value of 4, increasing the M_ν-sensitivity of the small-scale neutrino density.
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