Abstract. We have performed detailed studies of non-linear structure formation in cosmological models with light neutrinos. For the first time the effect of neutrino thermal velocities has been included in a consistent way, and the effect on the matter power spectrum is found to be significant. The effect is large enough to be measured in future, high precision surveys. Additionally, we provide a simple but accurate analytic expression for the suppression of fluctuation power due to massive neutrinos. Finally, we describe a simple and fast method for including the effect of massive neutrinos in large-scale N -body simulations which is accurate at the 1% level for m ν 0.15 eV.PACS numbers: 98.65. Dx, 95.35.+d, 14.60.Pq

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 m ν 0.5 eV at z = 0. This error scales approximately as ( m ν ) 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 m ν 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.PACS numbers: 98.65. Dx, 95.35.+d, 14.60.Pq

We use N -body simulations to find the effect of neutrino masses on halo properties, and investigate how the density profiles of both the neutrino and the dark matter components change as a function of the neutrino mass. We compare our neutrino density profiles with results from the N -one-body method and find good agreement. We also show and explain why the Tremaine-Gunn bound for the neutrinos is not saturated. Finally we study how the halo mass function changes as a function of the neutrino mass and compare our results with the Sheth-Tormen semi-analytic formulae. Our results are important for surveys which aim at probing cosmological parameters using clusters, as well as future experiments aiming at measuring the cosmic neutrino background directly.

We have observed oscillations in the nearby G2 subgiant star β Hyi using high-precision velocity observations obtained over more than a week with the HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb structure, as expected for solar-like oscillations, but with several l = 1 modes being strongly affected by avoided crossings. The data, combined with those we obtained five years earlier, allow us to identify 28 oscillation modes. By scaling the large frequency separation from the Sun, we measure the mean density of β Hyi to an accuracy of 0.6%. The amplitudes of the oscillations are about 2.5 times solar and the mode lifetime is 2.3 d. A detailed comparison of the mixed l = 1 modes with theoretical models should allow a precise estimate of the age of the star.

We present the first simulation capable of resolving the structure of neutrino clustering on Mpc scales. The method combines grid-and particle-based methods and achieves very good accuracy on both small and large scales, while keeping CPU consumption under control. Such simulations are not only ideal for calculating the non-linear matter power spectrum but also particularly relevant for studies of how neutrinos cluster in galaxy-or cluster-sized halos. We perform the largest neutrino Nbody simulation to date, effectively containing 10 different neutrino hot dark matter components with different thermal properties.PACS numbers: 98.65. Dx, 95.35.+d, 14.60.Pq