Efficient approximations of neutrino physics for three-dimensional simulations of stellar core collapse

Neutrino transport in spherically symmetric models of stellar core collapse and bounce has achieved a technically complete level, rewarded by the agreement among independent groups that a multi-dimensional treatment of the fluid-instabilities in the post-bounce phase is indispensable to model supernova explosions. While much effort is required to develop a reliable neutrino transport technique in axisymmetry, we explore neutrino physics approximations and parameterizations for an efficient three-dimensional simulation of the fluid-instabilities in the shock-heated matter that accumulates between the accretion shock and the protoneutron star. We demonstrate the reliability of a simple parameterization scheme in the collapse phase and extend our 3D magneto-hydrodynamical collapse simulations to a preliminary postbounce evolution. The growth of magnetic fields is investigated.Comment: 5 pages, 4 figures, in Proceedings of "Nuclei in the Cosmos IX, Geneva, Jun 25-30", associated movies are displayed at http://www.physik.unibas.ch/~liebend/displa

Precision measurement of cosmic magnification from 21 cm emitting galaxies

We show how precision lensing measurements can be obtained through the lensing magnification effect in high redshift 21cm emission from galaxies. Normally, cosmic magnification measurements have been seriously complicated by galaxy clustering. With precise redshifts obtained from 21cm emission line wavelength, one can correlate galaxies at different source planes, or exclude close pairs to eliminate such contaminations. We provide forecasts for future surveys, specifically the SKA and CLAR. SKA can achieve percent precision on the dark matter power spectrum and the galaxy dark matter cross correlation power spectrum, while CLAR can measure an accurate cross correlation power spectrum. The neutral hydrogen fraction was most likely significantly higher at high redshifts, which improves the number of observed galaxies significantly, such that also CLAR can measure the dark matter lensing power spectrum. SKA can also allow precise measurement of lensing bispectrum.Comment: 11 pages, 8 figures. Accepted to MNRAS. We deleted two figures and shortened the paper to meet MNRAS's requirement. All main results remain unchange

Precision era of the kinetic Sunyaev-Zeldovich effect: simulations, analytical models and observations and the power to constrain reionization

The kinetic SZ effect, which is the dominant CMB source at arc-minute scales and $\nu \sim 217$ Ghz, probes the ionized gas peculiar momentum up to the epoch of reionization and is a sensitive measure of the reionization history. We ran high resolution self-similar and $\Lambda$CDM hydro simulations and built an analytical model to study this effect. Our model reproduces the $\Lambda$CDM simulation results to several percent accuracy, passes various tests against self-similar simulations, and shows a wider range of applicability than previous analytical models. Our model in its continuous version is free of simulation limitations such as finite simulation box and finite resolution and allows an accurate prediction of the kinetic SZ power spectrum $C_l$. For the WMAP cosmology, we find $l^2C_l/(2\pi)\simeq 0.91 \times 10^{-12} [(1+z_{\rm reion})/10]^{0.34}(l/5000)^{0.23-0.015(z_{\rm reion}-9)}$ for the reionization redshift $6<z_{\rm reion}<20$ and $3000<l<9000$. The corresponding temperature fluctuation is several $\mu$K at these ranges. The dependence of $C_l$ on the reionization history allows an accurate measurement of the reionization epoch. For the Atacama cosmology telescope experiment, $C_l$ can be measured with $\sim 1$ accuracy. $C_l$ scales as $(\Omega_b h)^2 \sigma_8^{4\sim 6}$. Given cosmological parameters, ACT would be able to constrain $z_{\rm reion}$ with several percent accuracy. Some multi-reionization scenarios degenerate in the primary CMB temperature and TE measurement can be distinguished with $\sim 10 \sigma$ confidence.Comment: 14 pages, 7 figures. Accepted by MNRAS. We corrected the primary CMB power spectrum we used. We added discussions about the effects of lensing and relativistic SZ correctio. We withdraw a claim about the patchy reionizatio

Power Spectra in Global Defect Theories of Cosmic Structure Formation

An efficient technique for computing perturbation power spectra in field ordering theories of cosmic structure formation is introduced, enabling computations to be carried out with unprecedented precision. Large scale simulations are used to measure unequal time correlators of the source stress energy, taking advantage of scaling during matter and radiation domination, and causality, to make optimal use of the available dynamic range. The correlators are then re-expressed in terms of a sum of eigenvector products, a representation which we argue is optimal, enabling the computation of the final power spectra to be performed at high accuracy. Microwave anisotropy and matter perturbation power spectra for global strings, monopoles, textures and non-topological textures are presented and compared with recent observations.Comment: 4 pages, compressed and uuencoded RevTex file and postscript figure

Approaching the dynamics of hot nucleons in supernovae

All recent numerical simulations agree that stars in the main sequence mass range of 9-40 solar masses do not produce a prompt hydrodynamic ejection of the outer layers after core collapse and bounce. Rather they suggest that stellar core collapse and supernova explosion are dynamically distinct astrophysical events, separated by an unspectacular accretion phase of at least ~40 ms duration. As long as the neutrinospheres remain convectively stable, the explosion dynamics is determined by the neutrons, protons, electrons and neutrinos in the layer of impact-heated matter piling up on the protoneutron star. The crucial role of neutrino transport in this regime has been emphasized in many previous investigations. Here, we search for efficient means to address the role of magnetic fields and fluid instabilities in stellar core collapse and the postbounce phase.Comment: 4 pages, contribution to Nuclei in the Cosmos VIII, Jul. 19-23, submitted to Nucl. Phys.

FISH: A 3D parallel MHD code for astrophysical applications

FISH is a fast and simple ideal magneto-hydrodynamics code that scales to ~10 000 processes for a Cartesian computational domain of ~1000^3 cells. The simplicity of FISH has been achieved by the rigorous application of the operator splitting technique, while second order accuracy is maintained by the symmetric ordering of the operators. Between directional sweeps, the three-dimensional data is rotated in memory so that the sweep is always performed in a cache-efficient way along the direction of contiguous memory. Hence, the code only requires a one-dimensional description of the conservation equations to be solved. This approach also enable an elegant novel parallelisation of the code that is based on persistent communications with MPI for cubic domain decomposition on machines with distributed memory. This scheme is then combined with an additional OpenMP parallelisation of different sweeps that can take advantage of clusters of shared memory. We document the detailed implementation of a second order TVD advection scheme based on flux reconstruction. The magnetic fields are evolved by a constrained transport scheme. We show that the subtraction of a simple estimate of the hydrostatic gradient from the total gradients can significantly reduce the dissipation of the advection scheme in simulations of gravitationally bound hydrostatic objects. Through its simplicity and efficiency, FISH is as well-suited for hydrodynamics classes as for large-scale astrophysical simulations on high-performance computer clusters. In preparation for the release of a public version, we demonstrate the performance of FISH in a suite of astrophysically orientated test cases.Comment: 27 pages, 11 figure