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Showing papers on "Cosmology published in 2006"


Journal ArticleDOI
TL;DR: In this article, a simple cosmological model with only six parameters (matter density, Omega_m h^2, baryon density, BH 2, Hubble Constant, H_0, amplitude of fluctuations, sigma_8, optical depth, tau, and a slope for the scalar perturbation spectrum, n_s) was proposed to fit the three-year WMAP temperature and polarization data.
Abstract: A simple cosmological model with only six parameters (matter density, Omega_m h^2, baryon density, Omega_b h^2, Hubble Constant, H_0, amplitude of fluctuations, sigma_8, optical depth, tau, and a slope for the scalar perturbation spectrum, n_s) fits not only the three year WMAP temperature and polarization data, but also small scale CMB data, light element abundances, large-scale structure observations, and the supernova luminosity/distance relationship. Using WMAP data only, the best fit values for cosmological parameters for the power-law flat LCDM model are (Omega_m h^2, Omega_b h^2, h, n_s, tau, sigma_8) = 0.1277+0.0080-0.0079, 0.02229+-0.00073, 0.732+0.031-0.032, 0.958+-0.016, 0.089+-0.030, 0.761+0.049-0.048). The three year data dramatically shrink the allowed volume in this six dimensional parameter space. Assuming that the primordial fluctuations are adiabatic with a power law spectrum, the WMAP data_alone_ require dark matter, and favor a spectral index that is significantly less than the Harrison-Zel'dovich-Peebles scale-invariant spectrum (n_s=1, r=0). Models that suppress large-scale power through a running spectral index or a large-scale cut-off in the power spectrum are a better fit to the WMAP and small scale CMB data than the power-law LCDM model; however, the improvement in the fit to the WMAP data is only Delta chi^2 = 3 for 1 extra degree of freedom. The combination of WMAP and other astronomical data yields significant constraints on the geometry of the universe, the equation of state of the dark energy, the gravitational wave energy density, and neutrino properties. Consistent with the predictions of simple inflationary theories, we detect no significant deviations from Gaussianity in the CMB maps.

6,295 citations


Journal ArticleDOI
TL;DR: In this article, a simple cosmological model with only six parameters (matter density, Omega_m h^2, baryon density, BH density, Hubble Constant, H_0, amplitude of fluctuations, sigma_8, optical depth, tau, and a slope for the scalar perturbation spectrum, n_s) was proposed to fit the three-year WMAP temperature and polarization data.
Abstract: A simple cosmological model with only six parameters (matter density, Omega_m h^2, baryon density, Omega_b h^2, Hubble Constant, H_0, amplitude of fluctuations, sigma_8, optical depth, tau, and a slope for the scalar perturbation spectrum, n_s) fits not only the three year WMAP temperature and polarization data, but also small scale CMB data, light element abundances, large-scale structure observations, and the supernova luminosity/distance relationship. Using WMAP data only, the best fit values for cosmological parameters for the power-law flat LCDM model are (Omega_m h^2, Omega_b h^2, h, n_s, tau, sigma_8) = 0.1277+0.0080-0.0079, 0.02229+-0.00073, 0.732+0.031-0.032, 0.958+-0.016, 0.089+-0.030, 0.761+0.049-0.048). The three year data dramatically shrink the allowed volume in this six dimensional parameter space. Assuming that the primordial fluctuations are adiabatic with a power law spectrum, the WMAP data_alone_ require dark matter, and favor a spectral index that is significantly less than the Harrison-Zel'dovich-Peebles scale-invariant spectrum (n_s=1, r=0). Models that suppress large-scale power through a running spectral index or a large-scale cut-off in the power spectrum are a better fit to the WMAP and small scale CMB data than the power-law LCDM model: however, the improvement in the fit to the WMAP data is only Delta chi^2 = 3 for 1 extra degree of freedom. The combination of WMAP and other astronomical data yields significant constraints on the geometry of the universe, the equation of state of the dark energy, the gravitational wave energy density, and neutrino properties. Consistent with the predictions of simple inflationary theories, we detect no significant deviations from Gaussianity in the CMB maps.

6,002 citations


Journal ArticleDOI
TL;DR: In this article, the physics of the 21 cm transition were reviewed, focusing on processes relevant at high redshifts, and the insights to be gained from such observations were described.

1,315 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that it is possible to simultaneously reproduce both the local Tully-Fisher relation and luminosity function using semi-analytic techniques applied to the standard LCDM cosmology, thus contradicting previous studies of this issue.
Abstract: In Figure 6 we inadvertently labeled the proxy circular velocity as the virial velocity of the dark matter halo instead of what is actually plotted, the maximum circular velocity of the dark matter halo. The maximum halo circular velocity is a much better estimate of the disk V_c than is V_vir. This confusion influenced the discussion of the Tully-Fisher relation in our paper. In fact, Figure 6 demonstrates that it is possible to simultaneously reproduce both the local Tully-Fisher relation and luminosity function using semi-analytic techniques applied to the standard LCDM cosmology, thus contradicting previous studies of this issue and our own discussion in Section 3.6.

1,197 citations


Journal ArticleDOI
TL;DR: In this paper, a general scheme for modified $f(R)$ gravity reconstruction from any realistic Friedmann-Robertson-Walker (FRW) cosmology is developed, where the modified gravities are expressed implicitly (in terms of special functions) with late-time asymptotics of known type (for instance, the model with negative and positive powers of curvature).
Abstract: We develop the general scheme for modified $f(R)$ gravity reconstruction from any realistic Friedmann-Robertson-Walker (FRW) cosmology. We formulate several versions of modified gravity compatible with solar system tests where the following sequence of cosmological epochs occurs: (a) matter dominated phase (with or without usual matter), transition from deceleration to acceleration, accelerating epoch consistent with recent WMAP data, (b) $\ensuremath{\Lambda}\mathrm{CDM}$ cosmology without cosmological constant. As a rule, such modified gravities are expressed implicitly (in terms of special functions) with late-time asymptotics of known type (for instance, the model with negative and positive powers of curvature). In the alternative approach, it is demonstrated that even simple versions of modified gravity may lead to the unification of matter dominated and accelerated phases at the price of the introduction of compensating dark energy.

985 citations


Journal ArticleDOI
TL;DR: Weak gravitational lensing has several important effects on the cosmic microwave background (CMB): it changes the CMB power spectra, induces non-Gaussianities, and generates a B-mode polarization signal that is an important source of confusion for the signal from primordial gravitational waves.

981 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe how free-streaming massive neutrinos affect the evolution of cosmological perturbations, and summarize the current bounds on the sum of neutrino masses that can be derived from various combinations of data, including the most recent analysis by the WMAP team.

930 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe how free-streaming massive neutrinos affect the evolution of cosmological perturbations, and summarize the current bounds on the sum of neutrino masses that can be derived from various combinations of data, including the most recent analysis by the WMAP team.
Abstract: The present experimental results on neutrino flavour oscillations provide evidence for non-zero neutrino masses, but give no hint on their absolute mass scale, which is the target of beta decay and neutrinoless double-beta decay experiments. Crucial complementary information on neutrino masses can be obtained from the analysis of data on cosmological observables, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure. In this review we describe in detail how free-streaming massive neutrinos affect the evolution of cosmological perturbations. We summarize the current bounds on the sum of neutrino masses that can be derived from various combinations of cosmological data, including the most recent analysis by the WMAP team. We also discuss how future cosmological experiments are expected to be sensitive to neutrino masses well into the sub-eV range.

723 citations


Journal ArticleDOI
27 Apr 2006-Nature
TL;DR: This work has shown that the rich tapestry of present-day cosmic structure arose during the first instants of creation, where weak ripples were imposed on the otherwise uniform and rapidly expanding primordial soup.
Abstract: Research over the past 25 years has led to the view that the rich tapestry of present-day cosmic structure arose during the first instants of creation, where weak ripples were imposed on the otherwise uniform and rapidly expanding primordial soup. Over 14 billion years of evolution, these ripples have been amplified to enormous proportions by gravitational forces, producing ever-growing concentrations of dark matter in which ordinary gases cool, condense and fragment to make galaxies. This process can be faithfully mimicked in large computer simulations, and tested by observations that probe the history of the Universe starting from just 400,000 years after the Big Bang.

663 citations


Journal ArticleDOI
TL;DR: In this article, the authors determined the mass function in the concordance ΛCDM cosmology, as well as its uncertainty, using sixteen 10243 particle nested-volume dark matter simulations spanning a mass range of over 5 orders of magnitude.
Abstract: The predicted mass function of dark matter halos is essential in connecting observed galaxy-cluster counts and models of galaxy clustering to the properties of the primordial density field. We determine the mass function in the concordance ΛCDM cosmology, as well as its uncertainty, using sixteen 10243 particle nested-volume dark matter simulations spanning a mass range of over 5 orders of magnitude. Using the nested volumes and single-halo tests, we find and correct for a systematic error in the friends-of-friends halo-finding algorithm. We find a fitting form and full error covariance for the mass function that successfully describes the simulations' mass function and is well behaved outside the simulations' resolutions. Estimated forecasts of uncertainty in cosmological parameters from future cluster-count surveys receive a negligible contribution from remaining statistical uncertainties in the central cosmology multiplicity function. There exists a potentially nonnegligible cosmological dependence (nonuniversality) of the halo multiplicity function.

551 citations


Journal ArticleDOI
TL;DR: In this paper, the authors quantify all the effects that break the spherical symmetry of the three-dimensional 21 cm power spectrum and show that it will be difficult to place competitive constraints on cosmological parameters with any of the considered methods.
Abstract: A number of radio interferometers are currently being planned or constructed to observe 21 cm emission from reionization. Not only will such measurements provide a detailed view of that epoch, but, since the 21 cm emission also traces the distribution of matter in the universe, this signal can be used to constrain cosmological parameters. The sensitivity of an interferometer to the cosmological information in the signal may depend on how precisely the angular dependence of the 21 cm three-dimensional power spectrum can be measured. Using an analytic model for reionization, we quantify all the effects that break the spherical symmetry of the three-dimensional 21 cm power spectrum. We find that upcoming observatories will be sensitive to the 21 cm signal over a wide range of scales, from larger than 100 to as small as 1 comoving Mpc. Next, we consider three methods to measure cosmological parameters from the signal: (1) direct fitting of the density power spectrum to the signal, (2) using only the velocity field fluctuations in the signal, and (3) looking at the signal at large enough scales that all fluctuations trace the density field. With the foremost method, the first generation of 21 cm observations should moderately improve existing constraints on cosmological parameters for certain low-redshift reionization scenarios, and a 2 yr observation with the second-generation interferometer MWA5000 in combination with the CMB telescope Planck could improve constraints on Ω_w, Ω_(m)h^2, Ω_(b)h^2, Ω_ν, n_s, and α_s. If the universe is substantially ionized by z ~ 12 or if spin temperature fluctuations are important, we show that it will be difficult to place competitive constraints on cosmological parameters with any of the considered methods.

Journal ArticleDOI
TL;DR: In this article, the authors developed a unified phantom cosmology where the same scalar plays the role of early time (phantom) inflaton and late-time dark energy, and the recent transition from decelerating to accelerating phase is described too by the scalar field.

Journal ArticleDOI
TL;DR: In this paper, the authors considered the cross-correlation of two Michelson channels by calculating the optimal signal-to-noise ratio that can be achieved by combining the full set of interferometry variables that are available with a six link triangular interferometer.
Abstract: The detection of the cosmic microwave background radiation (CMB) was one of the most important cosmological discoveries of the last century. With the development of interferometric gravitational wave detectors, we may be in a position to detect the gravitational equivalent of the CMB in this century. The cosmic gravitational background (CGB) is likely to be isotropic and stochastic, making it difficult to distinguish from instrument noise. The contribution from the CGB can be isolated by cross-correlating the signals from two or more independent detectors. Here we extend previous studies that considered the cross-correlation of two Michelson channels by calculating the optimal signal-to-noise ratio that can be achieved by combining the full set of interferometry variables that are available with a six link triangular interferometer. In contrast to the two channel case, we find that the relative orientation of a pair of coplanar detectors does not affect the signal-to-noise ratio. We apply our results to the detector design described in the Big Bang Observer (BBO) mission concept study and find that the BBO could detect a background with Ωgw > 2.2 × 10−17.

Journal ArticleDOI
TL;DR: In this cosmological scenario, the early Hagedorn phase of string gas cosmology goes over smoothly into the radiation-dominated phase of standard cosmology, without having a period ofcosmological inflation.
Abstract: We study the generation of cosmological perturbations during the Hagedorn phase of string gas cosmology. Using tools of string thermodynamics we provide indications that it may be possible to obtain a nearly scale-invariant spectrum of cosmological fluctuations on scales which are of cosmological interest today. In our cosmological scenario, the early Hagedorn phase of string gas cosmology goes over smoothly into the radiation-dominated phase of standard cosmology, without having a period of cosmological inflation.

Journal ArticleDOI
TL;DR: In this paper, the authors consider the implications of the landscape paradigm for the large scale properties of the universe and argue that the overshoot problem, which in other settings would make it difficult to achieve slow roll inflation, actually favors such a cosmology, and they consider anthropic bounds on the value of the curvature and on the parameters of inflation.
Abstract: In this paper we consider the implications of the ``landscape paradigm [1], [2] for the large scale properties of the universe. The most direct implication of a rich landscape is that our local universe was born in a tunnelling event from a neighboring vacuum. This would imply that we live in an open FRW universe with negative spatial curvature. We argue that the ``overshoot problem, which in other settings would make it difficult to achieve slow roll inflation, actually favors such a cosmology. We consider anthropic bounds on the value of the curvature and on the parameters of inflation. When supplemented by statistical arguments these bounds suggest that the number of inflationary efolds is not very much larger than the observed lower bound. Although not statistically favored, the likelihood that the number of efolds is close to the bound set by observations is not negligible. The possible signatures of such a low number of efolds are briefly described.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the behavior of a dust-dominated inhomogeneous Lema\^{\i}tre-Tolman-Bondi universe model and confront it with various astrophysical observations, finding that such a model can easily explain the observed luminosity distance-redshift relation of supernovae without the need for dark energy, when the inhomogeneity is in the form of an underdense bubble centered near the observer.
Abstract: Recently, there have been suggestions that the apparent accelerated expansion of the universe is not caused by repulsive gravitation due to dark energy, but is rather a result of inhomogeneities in the distribution of matter. In this work, we investigate the behavior of a dust-dominated inhomogeneous Lema\^{\i}tre-Tolman-Bondi universe model, and confront it with various astrophysical observations. We find that such a model can easily explain the observed luminosity distance-redshift relation of supernovae without the need for dark energy, when the inhomogeneity is in the form of an underdense bubble centered near the observer. With the additional assumption that the universe outside the bubble is approximately described by a homogeneous Einstein-de Sitter model, we find that the position of the first peak in the cosmic microwave background (CMB) power spectrum can be made to match the WMAP observations. Whether or not it is possible to reproduce the entire CMB angular power spectrum in an inhomogeneous model without dark energy is still an open question.

Journal ArticleDOI
TL;DR: The Big Bang Observer is a proposed space-based gravitational-wave detector intended as a follow-on mission to the Laser Interferometer Space Antenna (LISA), designed to detect the stochastic background of gravitational waves from the early universe as discussed by the authors.
Abstract: The Big Bang Observer is a proposed space-based gravitational-wave detector intended as a follow on mission to the Laser Interferometer Space Antenna (LISA). It is designed to detect the stochastic background of gravitational waves from the early universe. We discuss how the interferometry can be arranged between three spacecraft for this mission and what research and development on key technologies are necessary to realize this scheme.

Journal ArticleDOI
TL;DR: In this paper, the interacting holographic dark energy model in a universe with spatial curvature was examined and it was shown that the model can accommodate a transition of the dark energy from ωD > − 1 to ω D − 1.

Journal ArticleDOI
TL;DR: In this article, the authors derived model-independent constraints on the dark energy density ρX(z) and the cosmic expansion rate H(z), and also derived constraints on wX (z) = w0 + w'z (with cutoff at z = 2).
Abstract: Type Ia supernova (SN Ia), galaxy clustering, and cosmic microwave background (CMB) anisotropy data provide complementary constraints on the nature of the dark energy in the universe. We find that the 3 yr Wilkinson Microwave Anisotropy Probe (WMAP) observations give a CMB shift parameter of R ≡ 1/2 dz'/H(z') = 1.70 ± 0.03. Using this new measured value of the CMB shift parameter, together with the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS), and SN Ia data from the HST/GOODS program and the first-year Supernova Legacy Survey, we derive model-independent constraints on the dark energy density ρX(z) and the cosmic expansion rate H(z). We also derive constraints on the dark energy equation of state wX(z) = w0 + w'z (with cutoff at z = 2) and wX(a) = w0 + (1 - a)wa. We find that current data provide slightly tighter constraints on ρX(z) and H(z) as free functions in redshift and roughly a factor of 2 improvement in constraining wX(z). A cosmological constant remains consistent with the data; however, uncertainties remain large for model-independent constraints of dark energy. A significant increase in the number of observed SNe Ia between redshifts of 1 and 2, complemented by improved BAO and weak-lensing cosmography measurements (as expected from the JEDI mission concept for the Joint Dark Energy Mission), will be required to dramatically tighten model-independent dark energy constraints.

Journal ArticleDOI
10 Aug 2006-Nature
TL;DR: Spectroscopic observations of stars in the metal-poor globular cluster NGC 6397 reveal trends of atmospheric abundance with evolutionary stage for various elements that are reproduced by stellar-evolution models with diffusion and turbulent mixing and conclude that diffusion is predominantly responsible for the low apparent stellar lithium abundance in the atmospheres of old stars.
Abstract: The measurement of the cosmic microwave background has strongly constrained the cosmological parameters of the Universe. When the measured density of baryons (ordinary matter) is combined with standard Big Bang nucleosynthesis calculations, the amounts of hydrogen, helium and lithium produced shortly after the Big Bang can be predicted with unprecedented precision. The predicted primordial lithium abundance is a factor of two to three higher than the value measured in the atmospheres of old stars. With estimated errors of 10 to 25%, this cosmological lithium discrepancy seriously challenges our understanding of stellar physics, Big Bang nucleosynthesis or both. Certain modifications to nucleosynthesis have been proposed, but found experimentally not to be viable. Diffusion theory, however, predicts atmospheric abundances of stars to vary with time, which offers a possible explanation of the discrepancy. Here we report spectroscopic observations of stars in the metal-poor globular cluster NGC6397 that reveal trends of atmospheric abundance with evolutionary stage for various elements. These element-specific trends are reproduced by stellar-evolution models with diffusion and turbulent mixing. We thus conclude that diffusion is predominantly responsible for the low apparent stellar lithium abundance in the atmospheres of old stars by transporting the lithium deep into the star.

Journal ArticleDOI
TL;DR: The first measurements of the weak gravitational lensing signal induced by the large-scale mass distribution in the universe from data obtained as part of the ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) are presented in this paper.
Abstract: We present the first measurements of the weak gravitational lensing signal induced by the large-scale mass distribution in the universe from data obtained as part of the ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in this analysis are from the Wide Synoptic Survey, which aims to image � 170 deg 2 in five filters. We have analyzed an effective area of � 22 deg 2 (31 pointings) of i 0 data spread over two of the three survey fields. These data are of excellent quality, and the results bode well for the remainder of the survey: we do not detect a significant ‘‘B’’ mode, suggesting that residual systematics are negligible at the current level of accuracy. Assuming a cold dark matter model and marginalizing over the Hubble parameter h 2½ 0:6; 0:8� , the source redshift distribution, and systematics, we constrain � 8, the amplitude of the matter power spectrum. At a fiducial matter density m ¼ 0:3 we find � 8 ¼ 0:85 � 0:06. This estimate is in excellent agreement with previous studies. A combination of our results with those from the Deep component of the CFHTLS enables us to place a constraint on a constant equation of state for the dark energy, based on cosmic shear data alone. We find that w0 < � 0:8 at 68% confidence. Subject headingg cosmology: observations — dark matter — gravitational lensing Online material: color figures

Journal ArticleDOI
TL;DR: In this paper, the authors show that an interaction between dark matter and dark energy generically results in an effective dark energy equation of state of w <-1, which is consistent with all current observations, the tightest constraint coming from estimates of the matter density at different redshifts.
Abstract: We show that an interaction between dark matter and dark energy generically results in an effective dark-energy equation of state of w<-1. This arises because the interaction alters the redshift dependence of the matter density. An observer who fits the data treating the dark matter as noninteracting will infer an effective dark-energy fluid with w<-1. We argue that the model is consistent with all current observations, the tightest constraint coming from estimates of the matter density at different redshifts. Comparing the luminosity and angular-diameter distance relations with {lambda}CDM and phantom models, we find that the three models are degenerate within current uncertainties but likely distinguishable by the next generation of dark-energy experiments.

Journal ArticleDOI
TL;DR: A new mechanism for creating the observed cosmic matter-antimatter asymmetry which satisfies all three Sakharov conditions from one common thread, gravitational waves is presented.
Abstract: We present a new mechanism for creating the observed cosmic matter-antimatter asymmetry which satisfies all three Sakharov conditions from one common thread, gravitational waves. We generate lepton number through the gravitational anomaly in the lepton number current. The source term comes from elliptically polarized gravity waves that are produced during inflation if the inflaton field contains a CP-odd component. The amount of matter asymmetry generated in our model can be of realistic size for the parameters within the range of some inflationary scenarios and grand unified theories.

Journal ArticleDOI
TL;DR: In this article, the authors derived upper and lower bounds for the basic physical parameters (mass-radius ratio, anisotropy, redshift and total energy) for arbitrary anisotropic general relativistic matter distributions in the presence of a cosmological constant.
Abstract: We derive the upper and lower limits for the basic physical parameters (mass-radius ratio, anisotropy, redshift and total energy) for arbitrary anisotropic general relativistic matter distributions in the presence of a cosmological constant. The values of these quantities are strongly dependent on the value of the anisotropy parameter (the difference between the tangential and radial pressure) at the surface of the star. In the presence of the cosmological constant, a minimum mass configuration with a given anisotropy does exist. Anisotropic compact stellar-type objects can be much more compact than the isotropic ones, and their radii may be close to their corresponding Schwarzschild radii. Upper bounds for the anisotropy parameter are also obtained from the analysis of the curvature invariants. General restrictions for the redshift and the total energy (including the gravitational contribution) for anisotropic stars are obtained in terms of the anisotropy parameter. Values of the surface redshift parameter greater than two could be the main observational signature for anisotropic stellar-type objects. © 2006 IOP Publishing Ltd.

Journal ArticleDOI
TL;DR: In this article, the authors used the conditional luminosity function (CLF) and data from the 2dFGRS to constrain the average relation between light and mass in a LCDM cosmology with Omegam=0.23 and sigma_8 = 0.74.
Abstract: We use the conditional luminosity function (CLF) and data from the 2dFGRS to constrain the average relation between light and mass in a LCDM cosmology with Omega_m=0.23 and sigma_8=0.74 (hereafter WMAP3 cosmology). Reproducing the observed luminosity dependence of the galaxy two-point correlation function results in average mass-to-light ratios that are about 35 percent lower than in a LCDM cosmology with Omega_m=0.3 and sigma_8=0.9 (hereafter WMAP1 cosmology). This removes an important problem with previous halo occupation models which had a tendency to predict cluster mass-to-light ratios that were too high. For the WMAP3 cosmology our model yields average mass-to-light ratios, central galaxy luminosities, halo occupation numbers, satellite fractions, and luminosity-gap statistics, that are all in excellent agreement with those obtained from a 2dFGRS group catalogue and from other independent studies. We also use our CLF model to compute the probability distribution P(M|L_cen), that a central galaxy of luminosity L_cen resides in a halo of mass M. We find this distribution to be much broader than what is typically assumed in HOD models, which has important implications for the interpretation of galaxy-galaxy lensing data. Finally, reproducing the luminosity dependence of the pairwise velocity dispersions in the 2dFGRS requires relatively low mass-to-light ratios for clusters and a satellite fraction that decreases strongly with increasing luminosity. This is only marginally consistent with our CLF constraints. We argue that a cosmology with parameters between those of the WMAP1 and WMAP3 cosmologies is likely to yield results with a higher level of consistency.

Journal ArticleDOI
TL;DR: In this article, the effects of photometric redshift uncertainties on weak-lensing tomography were analyzed and it was shown that dark energy parameters are sensitive to the shape and nature of outliers in the photo-z redshift distribution.
Abstract: We perform a systematic analysis of the effects of photometric redshift uncertainties on weak-lensing tomography. We describe the photo-z distribution with a bias and Gaussian scatter that are allowed to vary arbitrarily between intervals of δz = 0.1 in redshift. While the mere presence of bias and scatter does not substantially degrade dark energy information, uncertainties in both parameters do. For a fiducial next-generation survey each would need to be known to better than about 0.003-0.01 in redshift for each interval in order to lead to less than a factor of 1.5 increase in the dark energy parameter errors. The more stringent requirement corresponds to a larger dark energy parameter space, when redshift variation in the equation of state of dark energy is allowed. Of order 104-105 galaxies with spectroscopic redshifts fairly sampled from the source galaxy distribution will be needed to achieve this level of calibration. If the sample is composed of multiple galaxy types, a fair sample would be required for each. These requirements increase in stringency for more ambitious surveys; we quantify such scalings with a convenient fitting formula. No single aspect of a photometrically binned selection of galaxies such as their mean or median suffices, indicating that dark energy parameter determinations are sensitive to the shape and nature of outliers in the photo-z redshift distribution.

04 Apr 2006
TL;DR: The Planck satellite as mentioned in this paper is designed to extract essentially all of the information in the CMB temperature anisotropies, which can provide a unique probe of the thermal history of the universe during the time when the first stars and galaxies formed.
Abstract: For 40 years, the cosmic microwave background (CMB) has been the most important source of information about the geometry and contents of the Universe. Even so, only a small fraction of the information available in the CMB has been extracted to date. Planck, the third space CMB mission after COBE and WMAP, is designed to extract essentially all of the information in the CMB temperature anisotropies. Planck will also measure to high accuracy the polarization of CMB anisotropies, which encodes not only a wealth of cosmological information but also provides a unique probe of the thermal history of the Universe during the time when the first stars and galaxies formed. Polarization measurements may also detect the signature of a stochastic background of gravitational waves generated during inflation, 10^(-35) s after the Big Bang. This book describes the expected scientific output of the Planck mission, both cosmological and non-cosmological. Chapter 1 summarizes the experimental concept and the operation of the satellite. Chapter 2 covers the core cosmological science of the mission, describing the measurements that Planck will make, what we expect to learn from them about the geometry and contents of the Universe and about fundamental physics, and the combination of CMB data with other data to provide additional insights. Although the primary goal of Planck is cosmology, it will survey the whole sky with an unprecedented combination of frequency coverage, angular resolution, and sensitivity, providing data valuable for a broad range of astrophysics. Chapters 3, 4, and 5 describe non-cosmological astrophysical uses of the Planck data. This book can also be downloaded directly from http://www.rssd.esa.int/Planck .

Journal ArticleDOI
TL;DR: In this article, a joint analysis of the bispectrum and the power spectrum of the CMB data is presented, where the covariance properties of the two spectra are investigated.
Abstract: The present spatial distribution of galaxies in the Universe is non-Gaussian, with 40% skewness in $50{h}^{\ensuremath{-}1}\text{ }\text{ }\mathrm{Mpc}$ spheres, and remarkably little is known about the information encoded in it about cosmological parameters beyond the power spectrum. In this work we present an attempt to bridge this gap by studying the bispectrum, paying particular attention to a joint analysis with the power spectrum and their combination with CMB data. We address the covariance properties of the power spectrum and bispectrum including the effects of beat coupling that lead to interesting cross-correlations, and discuss how baryon acoustic oscillations break degeneracies. We show that the bispectrum has significant information on cosmological parameters well beyond its power in constraining galaxy bias, and when combined with the power spectrum is more complementary than combining power spectra of different samples of galaxies, since non-Gaussianity provides a somewhat different direction in parameter space. In the framework of flat cosmological models we show that most of the improvement of adding bispectrum information corresponds to parameters related to the amplitude and effective spectral index of perturbations, which can be improved by almost a factor of 2. Moreover, we demonstrate that the expected statistical uncertainties in ${\ensuremath{\sigma}}_{8}$ of a few percent are robust to relaxing the dark energy beyond a cosmological constant.

Journal ArticleDOI
08 Dec 2006-Science
TL;DR: Modeling a red giant with a fully three-dimensional hydrodynamic code and a full nucleosynthetic network finds that mixing arises in the supposedly stable and radiative zone between the hydrogen-burning shell and the base of the convective envelope, removing the threat that 3He production in low-mass stars poses to the Big Bang nucleosynthesis of 3He.
Abstract: Low-mass stars, ∼1 to 2 solar masses, near the Main Sequence are efficient at producing the helium isotope 3 He, which they mix into the convective envelope on the giant branch and should distribute into the Galaxy by way of envelope loss. This process is so efficient that it is difficult to reconcile the low observed cosmic abundance of 3 He with the predictions of both stellar and Big Bang nucleosynthesis. Here we find, by modeling a red giant with a fully three-dimensional hydrodynamic code and a full nucleosynthetic network, that mixing arises in the supposedly stable and radiative zone between the hydrogen-burning shell and the base of the convective envelope. This mixing is due to Rayleigh-Taylor instability within a zone just above the hydrogen-burning shell, where a nuclear reaction lowers the mean molecular weight slightly. Thus, we are able to remove the threat that 3 He production in low-mass stars poses to the Big Bang nucleosynthesis of 3 He.

Journal ArticleDOI
TL;DR: In this article, the authors proposed to generalize the dark energy equation of state (EoS) by introducing the relaxation equation for pressure which is equivalent to consideration of the inhomogeneous EoS cosmic fluid which often appears as the effective model from strings/brane-worlds.