Wayne Hu

Baryonic features in the matter transfer function

We provide scaling relations and fitting formulae for adiabatic cold dark matter cosmologies that account for all baryon effects in the matter transfer function to better than 10% in the large-scale structure regime. They are based upon a physically well-motivated separation of the effects of acoustic oscillations, Compton drag, velocity overshoot, baryon infall, adiabatic damping, Silk damping, and cold dark matter growth suppression. We also find a simpler, more accurate, and better motivated form for the zero-baryon transfer function than previous works. These descriptions are employed to quantify the amplitude and location of baryonic features in linear theory. While baryonic oscillations are prominent if the baryon fraction Ωb/Ω0 Ω0h2 + 0.2, the main effect in more conventional cosmologies is a sharp suppression in the transfer function below the sound horizon. We provide a simple but accurate description of this effect and stress that it is not well approximated by a change in the shape parameter Γ.

Models of f(R) Cosmic Acceleration that Evade Solar-System Tests

We study a class of metric-variation fRmodels that accelerates the expansion without a cosmological constant and satisfies both cosmological and solar-system tests in the small-field limit of the parameter space. Solar-system tests alone place only weak bounds on these models, since the additional scalar degree of freedom is locked to the high-curvature general-relativistic prediction across more than 25 orders of magnitude in density, out through the solar corona. This agreement requires that the galactic halo be of sufficient extent to maintain the galaxy at high curvature in the presence of the low-curvature cosmological background. If the galactic halo and local environment in fRmodels do not have substantially deeper potentials than expected inCDM , then cosmological field amplitudes jfRj * 10 � 6 will cause the galactic interior to evolve to low curvature during the acceleration epoch. Viability of large-deviation models therefore rests on the structure and evolution of the galactic halo, requiring cosmological simulations of fRmodels, and not directly on solar-system tests. Even small deviations that conservatively satisfy both galactic and solar-system constraints can still be tested by future, percent- level measurements of the linear power spectrum, while they remain undetectable to cosmological- distance measures. Although we illustrate these effects in a specific class of models, the requirements on fRare phrased in a nearly model-independent manner.

Power Spectra for Cold Dark Matter and Its Variants

The bulk of recent cosmological research has focused on the adiabatic cold dark matter model and its simple extensions. Here we present an accurate —tting formula that describes the matter transfer func- tions of all common variants, including mixed dark matter models. The result is a function of wavenum- ber, time, and six cosmological parameters: the massive neutrino density, number of neutrino species degenerate in mass, baryon density, Hubble constant, cosmological constant, and spatial curvature. We show how observational constraintse.g., the shape of the power spectrum, the abundance of clusters and damped Lya systems, and the properties of the Lya forestcan be extended to a wide range of cosmologies, which includes variations in the neutrino and baryon fractions in both high-density and low-density universes. Subject headings: cosmology: theorydark matterlarge-scale structure of universe

Report of the Dark Energy Task Force

Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science. These circumstances demand an ambitious observational program to determine the dark energy properties as well as possible.

Small scale cosmological perturbations: An Analytic approach

Through analytic techniques verified by numerical calculations, we establish general relations between the matter and cosmic microwave background (CMB) power spectra and their dependence on parameters on small scales. Fluctuations in the CMB, baryons, cold dark matter (CDM), and neutrinos receive a boost at horizon crossing. Baryon drag on the photons causes alternating acoustic peak heights in the CMB and is uncovered in its bare form under the photon diffusion scale. Decoupling of the photons at last scattering and of the baryons at the end of the Compton drag epoch freezes the diffusion-damped acoustic oscillations into the CMB and matter power spectra at different scales. We determine the dependence of the respective acoustic amplitudes and damping lengths on fundamental cosmological parameters. The baryonic oscillations, enhanced by the velocity overshoot effect, compete with CDM fluctuations in the present matter power spectrum. We present new exact analytic solutions for the cold dark matter fluctuations in the presence of a growth-inhibiting radiation and baryon background. Combined with the acoustic contributions and baryonic infall into CDM potential wells, this provides a highly accurate analytic form of the small-scale transfer function in the general case.

Fuzzy cold dark matter: the wave properties of ultralight particles.

There is an asymmetry between the mass of the electric charges, for example proton and electron, can understood by the asymmetrical Planck Distribution Law. This temperature dependent energy distribution is asymmetric around the maximum intensity, where the annihilation of matter and antimatter is a high probability event. The asymmetric sides are creating different frequencies of electromagnetic radiations being in the same intensity level and compensating each other. One of these compensating ratios is the electron – proton mass ratio. The lower energy side has no compensating intensity level, it is the dark energy and the corresponding matter is the dark matter.

Cosmic Microwave Background Anisotropies

▪ Abstract Cosmic microwave background (CMB) temperature anisotropies have and will continue to revolutionize our understanding of cosmology. The recent discovery of the previously predicted acoust...

Sample Variance Considerations for Cluster Surveys

We present a general statistical framework for describing the effect of sample variance in the number counts of virialized objects and examine its effect on cosmological parameter estimation. Specifically, we consider effects of sample variance on the power spectrum normalization and properties of dark energy extracted from current and future local and high-redshift samples of clusters. We show that for future surveys that probe ever lower cluster masses and temperatures, sample variance is generally comparable to or greater than shot noise and thus cannot be neglected in deriving precision cosmological constraints. For example, sample variance is usually more important than shot variance in constraints on the equation of state of the dark energy from z < 1 clusters. Although we found that effects of sample variance on the σ8-Ωm constraints from the current flux- and temperature-limited X-ray surveys are not significant, they may be important for future studies utilizing the shape of the temperature function to break the σ8-Ωm degeneracy. We also present numerical tests clarifying the definition of cluster mass employed in cosmological modeling and an accurate fitting formula for the conversion between different definitions of halo mass (e.g., virial vs. fixed overdensity).

Mass Reconstruction with Cosmic Microwave Background Polarization

Weak gravitational lensing by the intervening large-scale structure of the Universe induces high-order correlations in the cosmic microwave background (CMB) temperature and polarization fields. We construct minimum variance estimators of the intervening mass distribution out of the six quadratic combinations of the temperature and polarization fields. Polarization begins to assist in the reconstruction when E-mode mapping becomes possible on degree-scale fields, i.e. for an experiment with a noise level of ∼ 40� K-arcmin and beam of ∼ 7 ′ , similar to the Planck experiment; surpasses the temperature reconstruction at ∼ 26� K-arcmin and 4 ′ ; yet continues to improve the reconstruction until the lensing B-modes are mapped to l ∼ 2000 at ∼ 0.3� K-arcmin and 3 ′ . Ultimately, the correlation between the E and B modes can provide a high signal-to-noise mass map out to multipoles of L ∼ 1000, extending the range of temperature-based estimators by nearly an order of magnitude. We outline four applications of mass reconstruction: measurement of the linear power spectrum in projection to the cosmic variance limit out to L ∼ 1000 (or wavenumbers 0.002 ∼ k ∼ 0.2 in h/Mpc), cross-correlation with cosmic shear surveys to probe the evolution of structure tomographically, cross-correlation of the mass and temperature maps to probe the dark energy, and the separation of lensing and gravitational wave B-modes. Subject headings: cosmic microwave background – dark matter — large scale structure of universe

Foregrounds and Forecasts for the Cosmic Microwave Background

One of the main challenges facing upcoming cosmic microwave background (CMB) experiments will be to distinguish the cosmological signal from foreground contamination. We present a comprehensive treatment of this problem and study how foregrounds degrade the accuracy with which the Boomerang, MAP, and Planck experiments can measure cosmological parameters. Our foreground model includes not only the normalization, frequency dependence, and scale dependence for each physical component, but also variations in frequency dependence across the sky. When estimating how accurately cosmo- logical parameters can be measured, we include the important complication that foreground model parameters (we use about 500) must be simultaneously measured from the data as well. Our results are quite encouraging: despite all these complications, precision measurements of most cosmological param- eters are degraded by less than a factor of 2 for our main foreground model and by less than a factor of 5 in our most pessimistic scenario. Parameters measured though large-angle polarization signals suUer more degradation: up to 5 in the main model and 25 in the pessimistic case. The foregrounds that are potentially most damaging and therefore most in need of further study are vibrating dust emission and point sources, especially those in the radio frequencies. It is well known that E and B polarization contain valuable information about reionization and gravity waves, respectively. However, the cross- correlation between polarized and unpolarized foregrounds also deserves further study, as we —nd that it carries the bulk of the polarization information about most other cosmological parameters. Subject headings: cosmic microwave backgrounddiUuse radiationmethods: numerical ¨ polarization