376 research outputs found

### 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

### Likelihood Analysis of Cosmic Shear on Simulated and VIRMOS-DESCART Data

We present a maximum likelihood analysis of cosmological parameters from
measurements of the aperture mass up to 35 arcmin, using simulated and real
cosmic shear data. A four-dimensional parameter space is explored which
examines the mean density \Omega_M, the mass power spectrum normalization
\sigma_8, the shape parameter \Gamma and the redshift of the sources z_s.
Constraints on \Omega_M and \sigma_8 (resp. \Gamma and z_s) are then given by
marginalizing over \Gamma and z_s (resp. \Omega_M and \sigma_8). For a flat
LCDM cosmologies, using a photometric redshift prior for the sources and \Gamma
\in [0.1,0.4], we find \sigma_8=(0.57\pm0.04) \Omega_M^{(0.24\mp 0.18)
\Omega_M-0.49} at the 68% confidence level (the error budget includes
statistical noise, full cosmic variance and residual systematic). The estimate
of \Gamma, marginalized over \Omega_M \in [0.1,0.4], \sigma_8 \in [0.7,1.3] and
z_s constrained by photometric redshifts, gives \Gamma=0.25\pm 0.13 at 68%
confidence. Adopting h=0.7, a flat universe, \Gamma=0.2 and \Omega_m=0.3 we
find \sigma_8=0.98 \pm0.06 . Combined with CMB, our results suggest a non-zero
cosmological constant and provide tight constraints on \Omega_M and \sigma_8.
We finaly compare our results to the cluster abundance ones, and discuss the
possible discrepancy with the latest determinations of the cluster method. In
particular we point out the actual limitations of the mass power spectrum
prediction in the non-linear regime, and the importance for its improvement.Comment: 11 pages, submitted to A&

### Cosmology with gravitationally lensed repeating Fast Radio Bursts

High-precision cosmological probes have revealed a small but significant
tension between the parameters measured with different techniques, among which
there is one based on time delays in gravitational lenses. We discuss a new way
of using time delays for cosmology, taking advantage of the extreme precision
expected for lensed fast radio bursts (FRBs), which are short flashes of radio
emission originating at cosmological distances. With coherent methods, the
achievable precision is sufficient for measuring how time delays change over
the months and years, which can also be interpreted as differential redshifts
between the images. It turns out that uncertainties arising from the unknown
mass distribution of gravitational lenses can be eliminated by combining time
delays with their time derivatives. Other effects, most importantly relative
proper motions, can be measured accurately and disentangled from the
cosmological effects. With a mock sample of simulated lenses, we show that it
may be possible to attain strong constraints on cosmological parameters.
Finally, the lensed images can be used as galactic interferometer to resolve
structures and motions of the burst sources with incredibly high resolution and
help reveal their physical nature, which is currently unknown.Comment: minor revision, published in A&A, 15 page

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