156 research outputs found
Fast and Exact Spin-s Spherical Harmonic Transforms
We demonstrate a fast spin-s spherical harmonic transform algorithm, which is
flexible and exact for band-limited functions. In contrast to previous work,
where spin transforms are computed independently, our algorithm permits the
computation of several distinct spin transforms simultaneously. Specifically,
only one set of special functions is computed for transforms of quantities with
any spin, namely the Wigner d-matrices evaluated at {\pi}/2, which may be
computed with efficient recursions. For any spin the computation scales as
O(L^3) where L is the band-limit of the function. Our publicly available
numerical implementation permits very high accuracy at modest computational
cost. We discuss applications to the Cosmic Microwave Background (CMB) and
gravitational lensing.Comment: 22 pages, preprint format, 5 figure
Halo Concentration and the Dark Matter Power Spectrum
We explore the connection between halo concentration and the dark matter
power spectrum using the halo model. We fit halo model parameters to non-linear
power spectra over a large range of cosmological models. We find that the
non-linear evolution of the power spectrum generically prefers the
concentration at non-linear mass scale to decrease with the effective slope of
the linear power spectrum, in agreement with the direct analysis of the halo
structure in different cosmological models. Using these analyses, we compute
the predictions for non-linear power spectrum beyond the current resolution of
N-body simulations. We find that the halo model predictions are generically
below the analytical non-linear models, suggesting that the latter may
overestimate the amount of power on small scales.Comment: 7 pages, 6 figures, MNRAS accepte
Sunyaev-Zeldovich effect in WMAP and its effect on cosmological parameters
We use multi-frequency information in first year WMAP data to search for the
Sunyaev-Zeldovich (SZ) effect. WMAP has sufficiently broad frequency coverage
to constrain SZ without the addition of higher frequency data: the SZ power
spectrum amplitude is expected to increase 50% from W to Q frequency band.
This, in combination with the low noise in WMAP, allows us to strongly
constrain the SZ contribution. We derive an optimal frequency combination of
WMAP cross-spectra to extract SZ in the presence of noise, CMB, and radio point
sources, which are marginalized over. We find that the SZ contribution is less
than 2% (95% c.l.) at the first acoustic peak in W band. Under the assumption
that the removed radio point sources are not correlated with SZ this limit
implies sigma_8<1.07 at 95% c.l. We investigate the effect on the cosmological
parameters of allowing an SZ component. We run Monte Carlo Markov Chains with
and without an SZ component and find that the addition of SZ does not affect
any of the cosmological conclusions. We conclude that SZ does not contaminate
the WMAP CMB or change cosmological parameters, refuting the recent claims that
they may be corrupted.Comment: 10 pages, 5 figures, 2 tables. Submitted to Phys. Rev.
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