Cosmic Microwave Background Anisotropy Power Spectrum Research Articles

Perturbed recombination from inhomogeneous photon injection and application to accreting primordial black holes

Exotic electromagnetic energy injection in the early Universe may alter cosmological recombination, and ultimately cosmic microwave background (CMB) anisotropies. Moreover, if energy injection is inhomogeneous, it may induce a spatially-varying ionization fraction, and non-Gaussianity in the CMB. The observability of these signals, however, is contingent upon how far the injected particles propagate and deposit their energy into the primordial plasma, relative to the characteristic scale of energy injection fluctuations. In this study we inspect the spatial properties of energy deposition and perturbed recombination resulting from an inhomogeneous energy injection of sub-10 MeV photons, relevant to accreting primordial black holes (PBHs). We develop a novel Monte-Carlo radiation transport code accounting for all relevant photon interactions in this energy range, and including secondary electron energy deposition efficiency through a new analytic approximation. For a specified injected photon spectrum, the code outputs an injection-to-deposition Green's function depending on time and distance from the injection point. Combining this output with a linearized solution of the perturbed recombination problem, we derive time- and scale-dependent deposition-to-ionization Green's functions. We apply this general framework to accreting PBHs, whose luminosity is strongly spatially modulated by supersonic relative velocities between cold dark matter and baryons. We find that the resulting spatial fluctuations of the free-electron fraction are of the same magnitude as its mean deviation from standard recombination, from which current CMB power spectra constraints are derived. This work suggests that the sensitivity to accreting PBHs might be substantially improved by propagating these inhomogeneities to CMB anisotropy power spectra and non-Gaussian statistics, which we study in subsequent papers.

Cosmic microwave background constraints on primordial black hole dark matter

We revisit cosmic microwave background (CMB) constraints on primordial black hole dark matter. Spectral distortion limits from COBE/FIRAS do not impose a relevant constraint. Planck CMB anisotropy power spectra imply that primordial black holes with mBH≳ 5 M⊙ are disfavored. However, this is susceptible to sizeable uncertainties due to the treatment of the black hole accretion process. These constraints are weaker than those quoted in earlier literature for the same observables.

Extreme data compression for the CMB

We apply the Karhunen-Lo\'eve methods to cosmic microwave background (CMB) data sets, and show that we can recover the input cosmology and obtain the marginalized likelihoods in $\mathrm{\ensuremath{\Lambda}}$ cold dark matter cosmologies in under a minute, much faster than Markov chain Monte Carlo methods. This is achieved by forming a linear combination of the power spectra at each multipole $l$, and solving a system of simultaneous equations such that the Fisher matrix is locally unchanged. Instead of carrying out a full likelihood evaluation over the whole parameter space, we need evaluate the likelihood only for the parameter of interest, with the data compression effectively marginalizing over all other parameters. The weighting vectors contain insight about the physical effects of the parameters on the CMB anisotropy power spectrum ${C}_{l}$. The shape and amplitude of these vectors give an intuitive feel for the physics of the CMB, the sensitivity of the observed spectrum to cosmological parameters, and the relative sensitivity of different experiments to cosmological parameters. We test this method on exact theory ${C}_{l}$ as well as on a Wilkinson Microwave Anisotropy Probe (WMAP)-like CMB data set generated from a random realization of a fiducial cosmology, comparing the compression results to those from a full likelihood analysis using CosmoMC. After showing that the method works, we apply it to the temperature power spectrum from the WMAP seven-year data release, and discuss the successes and limitations of our method as applied to a real data set.

Naturally large tensor-to-scalar ratio in inflation

Recently, BICEP2 measurements of the cosmic microwave background (CMB) $B$-mode polarization at degree angular scales has indicated the presence of tensor modes with a high tensor-to-scalar ratio of $r=0.2$ when assuming nearly scale-invariant tensor and scalar spectra, although the signal may be contaminated by dust emission as implied by the recent {\em Planck} polarization data. This result is in conflict with the {\em Planck} best-fit Lambda Cold Dark Model with $r<0.11$. Due to the fact that inflaton has to be interacting with other fields so as to convert its potential energy into radiation to reheat the Universe, the interacting inflaton may result in a suppression of the scalar spectrum at large scales. This suppression has been used to explain the observed low quadrupole in the CMB anisotropy. In this paper, we show that a combination of the tensor modes measured by BICEP2 and the large-scale suppressed scalar modes contributes to the CMB anisotropy in such a way that the resultant CMB anisotropy and polarization power spectra are consistent with both {\em Planck} and BICEP2 data. We also project our findings to cases in which $r$ may become reduced in future CMB polarization measurements.

IMPACTS OF DARK STARS ON REIONIZATION AND SIGNATURES IN THE COSMIC MICROWAVE BACKGROUND

We perform a detailed and systematic investigation of the possible impacts of dark stars upon the reionization history of the Universe, and its signatures in the cosmic microwave background (CMB). We compute hydrogen reionization histories, CMB optical depths and anisotropy power spectra for a range of stellar populations including dark stars. If dark stars capture large amounts of dark matter via nuclear scattering, reionization can be substantially delayed, leading to decreases in the integrated optical depth to last scattering and large-scale power in the EE polarization power spectrum. Using the integrated optical depth observed by WMAP7, in our canonical reionization model we rule out the section of parameter space where dark stars with high scattering-induced capture rates tie up more than ~90% of all the first star-forming baryons, and live for over ~250 Myr. When nuclear scattering delivers only moderate amounts of dark matter, reionization can instead be sped up slightly, modestly increasing the CMB optical depth. If dark stars do not obtain any dark matter via nuclear scattering, effects upon reionization and the CMB are negligible. The effects of dark stars upon reionization and its CMB markers can be largely mimicked or compensated for by changes in the existing parameters of reionization models, making dark stars difficult to disentangle from astrophysical uncertainties, but also widening the range of standard parameters in reionization models that can be made consistent with observations.

Evolution of the cosmic microwave background

We discuss the time dependence and future of the Cosmic Microwave Background (CMB) in the context of the standard cosmological model, in which we are now entering a state of endless accelerated expansion. The mean temperature will simply decrease until it reaches the effective temperature of the de Sitter vacuum, while the dipole will oscillate as the Sun orbits the Galaxy. However, the higher CMB multipoles have a richer phenomenology. The CMB anisotropy power spectrum will for the most part simply project to smaller scales, as the comoving distance to last scattering increases, and we derive a scaling relation that describes this behaviour. However, there will also be a dramatic increase in the integrated Sachs-Wolfe contribution at low multipoles. We also discuss the effects of tensor modes and optical depth due to Thomson scattering. We introduce a correlation function relating the sky maps at two times and the closely related power spectrum of the difference map. We compute the evolution both analytically and numerically, and present simulated future sky maps.

Observational test of holographic inflation

Observational consequences of inflationary cosmology in the holographic dual of the Randall-Sundrum type II braneworld scenario, as motivated by the anti-de Sitter/conformal field theory correspondence, are investigated. High energy corrections to the standard four-dimensional Friedmann equation induce a corresponding modification to the form of the single-field inflationary consistency equation based on Einstein gravity. The degree of departure from the standard expression is determined by the ratio, $r$, of the primordial tensor and scalar perturbation amplitudes and the coefficient, $c$, of the conformal anomaly in the dual gauge theory. It is found that a necessary condition for detecting such a correction with the next generation of cosmic microwave background (CMB) polarization experiments is that $r\ensuremath{\ge}0.06$. The bound is tightened to $r&gt;0.3$ for values of the central charge that are compatible with known compactifications of type IIB string theory as parametrized in terms of $F$-theory compactification on Calabi-Yau four-folds. This is close to the present upper bounds inferred from combined observations of the CMB anisotropy power spectrum and high redshift surveys. We conclude that if such modifications to the inflationary consistency equation are to be observable, the gravitational wave background should be detected in the near future. A further consequence of the nonstandard dynamics at high energies is that the initial state of the universe is a quiescent singularity with a finite density and pressure.

Second-order gravitational effects of local inhomogeneities on CMB anisotropies in nonzero-Λflat cosmological models

Nonlinear gravitational effects of large-scale local inhomogeneities on cosmic microwave background (CMB) anisotropies are studied, based on the relativistic second-order theory of perturbations in nonzero-$\ensuremath{\Lambda}$ flat cosmological models, which has been analytically derived by the present author, and on the second-order formula of CMB anisotropies derived by Mollerach and Matarrese. In this paper we derive the components of the CMB anisotropy power spectra in the range of $l=1\mathrm{\text{\ensuremath{-}}}22$ which are caused by asymmetric local inhomogeneities on scales of 300 Mpc. Using our results it is found that there is a possibility to explain the small north-south asymmetry of CMB anisotropies which has recently been observed.

Indirect limit on the amplitude of primordial gravitational wave background from CMB-galaxy cross correlation

While large scale cosmic microwave background (CMB) anisotropies involve a combination of the scalar and tensor fluctuations, the scalar amplitude can be independently determined through the CMB-galaxy cross correlation. Using recently measured cross correlation amplitudes, arising from the cross correlation between galaxies and the integrated Sachs-Wolfe (ISW) effect in CMB anisotropies, we obtain a constraint r<0.5 at 68% confidence level on the tensor-to-scalar fluctuation amplitude ratio. The data also allow us to exclude gravity waves at a level of a few percent, relative to the density field, in a low-Lambda dominated universe ({omega}{sub {lambda}}{approx}0.5). In future, joining cross correlation ISW measurements, which captures cosmological parameter information, with independent determinations of the matter density and CMB anisotropy power spectrum, may constrain the tensor-to-scalar ratio to a level above 0.05. This value is the ultimate limit on tensor-to-scalar ratio from temperature anisotropy maps when all other cosmological parameters except for the tensor amplitude are known and the combination with CMB-galaxy correlation allows this limit to be reached easily be accounting for degeneracies in certain cosmological parameters.

The cosmic microwave background power spectrum out to = 1400 measured by the Very Small Array

We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2° at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles = 160 and 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall-off in power at high f and starts to constrain the position and height of a fourth peak.

Binned Cosmic Microwave Background Anisotropy Power Spectra: Peak Location

We use weighted mean and median statistics techniques to combine individual cosmic microwave background (CMB) anisotropy detections and determine binned, multipole-space, CMB anisotropy power spectra. The resultant power spectra are peaked. The derived weighted-mean CMB anisotropy power spectrum is not a good representation of the individual measurements in a number of multipole-space bins, if the CMB anisotropy is Gaussian and correlations between individual measurements are small. This could mean that some observational error bars are underestimated, possibly as a consequence of undetected systematic effects. Discarding the most discrepant 5% of the measurements alleviates but does not completely resolve this problem. The median-statistics power spectrum of this culled data set is not as constraining as the weighted-mean power spectrum. Nevertheless it indicates that there is more power at multipoles $\ell \sim 150-250$ than is expected in an open cold dark matter (CDM) model, and it is more consistent with a flat CDM model. Unlike the weighted-mean power spectrum, the median-statistics power spectrum at $\ell \sim 400-500$ does not exclude a second peak in the flat CDM model.

Probing the Evolution of the Gas Mass Fraction with the Sunyaev-Zeldovich Effect

Study of the primary anisotropies of the Cosmic Microwave Background (CMB) can be used to determine the cosmological parameters to a very high precision. The power spectrum of the secondary CMB anisotropies due to the thermal Sunyaev-Zel'dovich Effect (SZE) by clusters of galaxies, can then be studied, to constrain more cluster specific properties (like gas mass). We show the SZE power spectrum from clusters to be a sensitive probe of any possible evolution (or constancy) of the gas mass fraction. The position of the peak of the SZE power spectrum is a strong discriminatory signature of different gas mass fraction evolution models. For example, for a flat universe, there can be a difference in the $l$ values (of the peak) of {\it as much as 3000} between a constant gas mass fraction model and an evolutionary one. Moreover, observational determination of power spectrum, from blank sky surveys, is devoid of any selection effects that can possibly affect targeted X-ray or radio studies of gas mass fractions in galaxy clusters.

CMB anisotropy experiments

Anisotropies in the cosmic microwave background (CMB) encode information about the evolution and development of the universe. Quality observations of CMB anisotropies can provide a very strong test of cosmological models and provide high precision determination of major cosmological parameters. This paper provides a review of the COBE DMR results, the current status of the measurements of the CMB anisotropy power spectrum and then focuses current and future programs including both suborbit al observations and the two selected satellite missions: the NASA MidEX mission MAP and the ESA M3 mission Max Planck Surveyor. This review includes both a description of the experimental programs and the expected quality level of results.

Determination of Cosmological Parameters by Cosmic Microwave Background

After the sensational discovery of Cosmic Microwave Background (CMB) anisotropies by Differential Microwave Radiometer (DMR) boarded on the Cosmic Background Explore (COBE) (Smoot et al. 1992), the number of observational data of temperature fluctuations have been rapidly increasing (see e.g., White, Scott and Silk 1994) together with the understanding of physical processes of evolution of CMB anisotropies. Nowadays, CMB anisotropies are becoming one of the key observational object in the modern cosmology. CMB anisotropies provide us direct information at last scattering surface, i.e., redshift z ≈ 1000. Since the shape of the angular power spectrum of CMB anisotropies is highly sensitive to geometry of the universe, cosmological models and cosmological parameters, i.e., density parameter Ω0, Hubble constant h which is normalized by 100km/s/Mpc, cosmological constant Λ, baryon density ΩB and so on, CMB anisotropies are expected to be a new tool to understand our universe. Moreover, we can obtain information of thermal history of the universe after recombination (through the formation of secondary fluctuations and damping of primary fluctuations), physics of clusters of galaxies (through the Sunyaev-Zeldovich effect) and non-linear structure of the universe (through the gravitational lensing effect) from CMB anisotropies.

Foregrounds Removal and CMB Fluctuations in a Multiband Anisotropy Experiment: ARGO 1993

We present the results of a diffuse radiation survey carried out at millimeter and submillimeter wavelengths in the Aries and Taurus sky regions. A balloon-borne telescope with 086 FWHM resolution and four millimeter-wave bands scanned 147 independent sky directions. From the multiband observations we were able to separate two independent components: thermal emission from cirrus dust and cosmic microwave background (CMB) temperature fluctuations. A statistically significant detection of anisotropies is found in the data of the CMB channel: ΔTsky = (24 ± 7) μK rms (95% CL plus 10% calibration error). Assuming uncorrelated Gaussian temperature fluctuations we find a band averaged estimate of the CMB anisotropy power spectrum Cl = (20 ± 9) μK2 at l ≃ 110. The data are consistent with anisotropies in a "standard" Ωb = 0.05, n = 1 model normalized to the rms anisotropy detected by COBE Differential Microwave Radiometers.

Cosmic Background Anisotropies in Cold Dark Matter Cosmology

view Abstract Citations (455) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic Background Anisotropies in Cold Dark Matter Cosmology Sugiyama, Naoshi Abstract Cosmic microwave background (CMB) anisotropies and density fluctuations are calculated for flat cold dark matter (CDM) models with a wide range of parameters, viz., Ω0, h, and ΩB, for standard recombination and for various epochs of reionization. Tables of the power spectrum of CMB anisotropies in the form of C1 values as a function of l are presented. Although the Harrison-Zeldovich initial spectrum is assumed in these tables, we present simple approximations for obtaining the C1 values corresponding to a tilted spectrum from those with a Harrison-Zeldovich spectrum. Values of σ8 are derived for the matter density spectrum, with α(10°), fixed Qrms-PS and COBE Differential Microwave Radiometer (DMR) 2 yr normalizations. Simple modifications of the fitting formula for the density transfer function are given which are applicable for models with high baryon density. By using both numerical results and these fitting formulae, we calculate the relation between α8 and Qrms-PS and find good agreement. In addition, the velocity fields are calculated. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1995 DOI: 10.1086/192220 arXiv: arXiv:astro-ph/9412025 Bibcode: 1995ApJS..100..281S Keywords: COSMOLOGY: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: THEORY; COSMOLOGY: DARK MATTER; Astrophysics E-Print: 30 pages including 10 figures, uuencoded comressed Postscript. 3 figures are missing. A complete version is available at anonymous ftp site ftp://pac2.berkeley.edu/pub/sugiyama/sugiyama.uu Tables (39pages) are also available at ftp://pac2.berkeley.edu/pub/sugiyama/tables.ps (and tables.tex) Replaced because one new figure is added and some figures are modified full text sources arXiv | ADS | data products CDS (2) Related Materials (1) Catalog: 1996yCat..21000281S