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 [ 1 ] , 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 .