νCONCEPT: cosmological neutrino simulations from the non-linear Boltzmann hierarchy

Abstract

In this paper the non-linear effect of massive neutrinos on cosmological structures is studied in a conceptually new way. We have solved the non-linear continuity and Euler equations for the neutrinos on a grid in real space in N -body simulations, and closed the Boltzmann hierarchy at the non-linear Euler equation using the stress and pressure perturbations from linear theory. By comparing with state-of-the art cosmological neutrino simulations, we are able to simulate the non-linear neutrino power spectrum very accurately. This translates into a negligible error in the matter power spectrum, and so our νconcept code is ideally suited for extracting the neutrino mass from future high precision non-linear observational probes such as EUCLID.

Fully relativistic treatment of light neutrinos in N-body simulations

“…In order to test the effect of massive neutrinos including GR corrections we perform a suite of N -body simulations, primarily using the publicly available concept N -body solver [18]. All concept simulations in this work use cosmological parameters as listed in table 1.…”

“…with θ tot the total peculiar velocity divergence of all species and w α =P α /ρ α the equation of state parameter of species α (both obtainable from class), after which we add δρ Nb γ and δρ Nb ν to δρ Nb metric , resulting in δρ Nb GR . The realisation of this δρ Nb GR (k) on a grid in real space is done using the formalism outlined in appendix A of [18].…”

“…We initialise the simulation using class in the same way as was described in [18]. Initial conditions for the density and velocity fields are generated using the N -body gauge δ cdm+b and θ cdm+b transfer functions from class at the initialisation time, i.e.…”

“…Finally, there are hybrid schemes coupling the two approaches [16], as well as approaches based on other approximate solutions (e.g. [17,18])…”

Massive neutrinos and degeneracies in Lyman-alpha forest simulations

“…Including massive neutrinos in cosmological simulations presents its own set of technical challenges [36][37][38][39][40]. Neutrinos are often included as another species of particle in the simulation alongside the CDM and baryons [41][42][43].…”