Grid Based Linear Neutrino Perturbations in Cosmological N-body   Simulations
  We present a novel, fast and precise method for including the effect of light neutrinos in cosmological N-body simulations. The effect of the neutrino component is included by using the linear theory neutrino perturbations in the calculation of the gravitational potential in the N-body simulation. By comparing this new method with the full non-linear evolution first presented in \cite{Brandbyge1}, where the neutrino component was treated as particles, we find that the new method calculates the matter power spectrum with an accuracy better than 1% for \sum m_\nu \lesssim 0.5 eV at z = 0. This error scales approximately as (\sum m_\nu)^2, making the new linear neutrino method extremely accurate for a total neutrino mass in the range 0.05 - 0.3 eV. At z = 1 the error is below 0.3% for \sum m_\nu \lesssim 0.5 eV and becomes negligible at higher redshifts. This new method is computationally much more efficient than representing the neutrino component by N-body particles. 
Jacob Brandbyge, Steen Hannestad