An optimal nonlinear method for simulating relic neutrinos
Abstract
Cosmology places the strongest current limits on the sum of neutrino masses. Future observations will further improve the sensitivity and this will require accurate cosmological simulations to quantify possible systematic uncertainties and to make predictions for nonlinear scales, where much information resides. However, shot noise arising from neutrino thermal motions limits the accuracy of simulations. In this paper, we introduce a new method for simulating largescale structure formation with neutrinos that accurately resolves the neutrinos down to small scales and significantly reduces the shot noise. The method works by tracking perturbations to the neutrino phasespace distribution with particles and reduces shot noise in the power spectrum by a factor of $\mathcal {O}\left(10^2\right)$ at z = 0 for minimal neutrino masses and significantly more at higher redshifts, without neglecting the backreaction caused by neutrino clustering. We prove that the method is part of a family of optimal methods that minimize shot noise subject to a maximum deviation from the nonlinear solution. Compared to other methods, we find per mille level agreement in the matter power spectrum and per cent level agreement in the largescale neutrino bias, but large differences in the neutrino component on small scales. A basic version of the method can easily be implemented in existing Nbody codes and allows neutrino simulations with significantly reduced particle load. Further gains are possible by constructing background models based on perturbation theory. A major advantage of this technique is that it works well for all masses, enabling a consistent exploration of the full neutrino parameter space.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2021
 DOI:
 10.1093/mnras/stab2260
 arXiv:
 arXiv:2010.07321
 Bibcode:
 2021MNRAS.507.2614E
 Keywords:

 neutrinos;
 largescale structure of Universe;
 cosmology: theory;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 16 pages, 10 figures, submitted to MNRAS