CMB Anisotropy Power Spectrum Research Articles

CMB and BBN constraints on evaporating primordial black holes revisited

We derive new CMB anisotropy power spectrum and BBN constraints for evaporating primordial black holes with mass between 1011 g and 1016 g by explicitly solving the electromagnetic particle cascades of emitted particles and the deposition of this emitted energy to the background baryon-photon plasma. We show that the CMB anisotropies can provide stronger constraints compared to BBN and CMB spectral distortions on black holes with masses as small as MBH=1.1× 1013 g, a slightly smaller mass than what has been considered in literature until now. We also show that, with more up-to-date data on abundances of deuterium and helium-3, BBN constraints are strengthened significantly. The abundance of these primordial black holes constrains the epoch of inflation 0∼ 4 e-folds after the epoch constrained by the CMB observations.

CMB anisotropy and BBN constraints on pre-recombination decay of dark matter to visible particles

Injection of high energy electromagnetic particles around the recombination epoch can modify the standard recombination history and therefore the CMB anisotropy power spectrum. Previous studies have put strong constraints on the amount of electromagnetic energy injection around the recombination era (redshifts z≲ 4500). However, energy injected in the form of energetic (> keV) visible standard model particles is not deposited instantaneously. The considerable delay between the time of energy injection and the time when all energy is deposited to background baryonic gas and CMB photons, together with the extraordinary precision with which the CMB anisotropies have been measured, means that CMB anisotropies are sensitive to energy that was injected much before the epoch of recombination. We show that the CMB anisotropy power spectrum is sensitive to energy injection even at z = 10000, giving stronger constraints compared to big bang nucleosynthesis and CMB spectral distortions. We derive, using Planck CMB data, the constraints on long-lived unstable particles decaying at redshifts z≲ 10000 (lifetime τX≳ 1011s) by explicitly evolving the electromagnetic cascades in the expanding Universe, thus extending previous constraints to lower particle lifetimes. We also revisit the BBN constraints and show that the delayed injection of energy is important for BBN constraints. We find that the constraints can be weaker by a factor of few to almost an order of magnitude, depending on the energy, when we relax the quasi-static or on-the-spot assumptions.

Disformal transformations on the CMB

In this work we study the role of disformal transformation on cosmological backgrounds and its relation to the speed of sound for tensor modes. A speed different from one for tensor modes can arise in several contexts, such as Galileons theories or massive gravity, nevertheless the speed is very constrained to be one by observations of gravitational wave emission. It has been shown that in inflation a disformal transformation allows to set the speed for tensor modes to one without making changes to the curvature power spectrum. Here we show that this invariance does not hold when considering the CMB anisotropy power spectrum. It turns out that the after doing the transformation there is an imprint on the acoustic peaks and the diffusion damping. This has interesting consequences; here we explore quartic galileon theories which allow a modified speed for tensor modes. For these theories the transformation can be used to constraint the parameter space in different regimes.

Large angular scale CMB anisotropy from an excited initial mode**Supported by the Islamic Azad University, Rasht Branch, Rasht, Iran

According to inflationary cosmology, the CMB anisotropy gives an opportunity to test predictions of new physics hypotheses. The initial state of quantum fluctuations is one of the important options at high energy scale, as it can affect observables such as the CMB power spectrum. In this study a quasi-de Sitter inflationary background with approximate de Sitter mode function built over the Bunch-Davies mode is applied to investigate the scale-dependency of the CMB anisotropy. The recent Planck constraint on spectral index motivated us to examine the effect of a new excited mode function (instead of pure de Sitter mode) on the CMB anisotropy at large angular scales. In so doing, it is found that the angular scale-invariance in the CMB temperature fluctuations is broken and in the limit ℓ < 200 a tiny deviation appears. Also, it is shown that the power spectrum of CMB anisotropy is dependent on a free parameter with mass dimension H << M* < Mp and on the slow-roll parameter ϵ.

Neutrinos in the holographic dark energy model: constraints from latest measurements of expansion history and growth of structure

The model of holographic dark energy (HDE) with massive neutrinos and/or dark radiation is investigated in detail. The background and perturbation evolutions in the HDE model are calculated. We employ the PPF approach to overcome the gravity instability difficulty (perturbation divergence of dark energy) led by the equation-of-state parameter w evolving across the phantom divide w=−1 in the HDE model with c<1. We thus derive the evolutions of density perturbations of various components and metric fluctuations in the HDE model. The impacts of massive neutrino and dark radiation on the CMB anisotropy power spectrum and the matter power spectrum in the HDE scenario are discussed. Furthermore, we constrain the models of HDE with massive neutrinos and/or dark radiation by using the latest measurements of expansion history and growth of structure, including the Planck CMB temperature data, the baryon acoustic oscillation data, the JLA supernova data, the Hubble constant direct measurement, the cosmic shear data of weak lensing, the Planck CMB lensing data, and the redshift space distortions data. We find that ∑ mν<0.186 eV (95% CL) and Neff=3.75+0.28−0.32 in the HDE model from the constraints of these data.

Possible indication for non-zero neutrino mass and additional neutrino species from cosmological observations

The constraints on total neutrino mass and effective number of neutrino species based on CMB anisotropy power spectrum, Hubble constant, baryon acoustic oscillations and galaxy cluster mass function data are presented. It is shown that the discrepancies between various cosmological data in Hubble constant and density fluctuation amplitude, measured in standard LCDM cosmological model, can be eliminated if more than standard effective number of neutrino species and non-zero total neutrino mass are considered. This extension of LCDM model appears to be \approx 3 \sigma\ significant when all cosmological data are used. The model with approximately one additional neutrino type, N_eff \approx 4, and with non-zero total neutrino mass, \approx 0.5 eV, provide the best fit to the data. In the model with only one massive neutrino the upper limits on neutrino mass are slightly relaxed. It is shown that these deviations from LCDM model appear mainly due to the usage of recent data on the observations of baryon acoustic oscillations. Larger than standard number of neutrino species is measured mainly due to the comparison of the BAO data with direct measurements of Hubble constant, which was already noticed earlier. As it is shown below, the data on galaxy cluster mass function in this case give the measurement of non-zero neutrino mass.

CMB anisotropies induced by tensor modes in Massive Gravity

We study Gravitational Waves (GWs) in the context ofMassive Gravity, an extension to General Relativity (GR) where thefluctuations of the metric have a nonzero mass, and specificallyinvestigate the effect of the tensor modes on the Cosmic MicrowaveBackground (CMB) anisotropies. We first study the time evolutionof the tensor modes in Massive Gravity and show that there is agraviton mass limit ml = 10−66g ∼ 10−29cm−1, so thatfor masses m ⩽ ml the tensor perturbations in Massive Gravityare indistinguishable from the corresponding ones in GR. Also, weshow that short wavelength massive modes behave almostindistinguishably from their massless counterparts. Later on, weshow that massive gravitons with masses within the range m = 10−27cm−1 - m = 10−26cm−1 would leave a clearsignature on the lower multipoles (ℓ < 30) in the CMBanisotropy power spectrum. Hence, our results indicate that CMBanisotropies measurements might be decisive to show whether thetensor modes are massive or not.

Bayesian Joint Estimation of Non-Gaussianity and the Power Spectrum

This paper gives a summary of our rigorous, non-perturbative, Bayesian framework which enables one jointly to test Gaussianity and estimate the power spectrum of CMB anisotropies. A detailed and thorough presentation of this new technique has been given in Rocha et al. 2000. There we apply our method to Very Small Array (VSA) simulations based on signal Gaussianity, showing that out algorithm is indeed not biased.

The shape of the CMB power spectrum

The recent WMAP data represent a milestone in cosmology and help constrain cosmological parameters with unprecedented accuracy. In this work, we combine the WMAP data with previous CMB anisotropy measurements at smaller angular scales to characterise the shape of the CMB anisotropy power spectrum. We carry out a phenomenological analysis of the data. By allowing non-physical shapes of the power spectrum we analyse high and low frequency experiments separately and together. We find that WMAP dramatically constrains the power spectrum up to ℓ∼700. On smaller scales, the data show discrepancies that can be associated with experimental systematics. If we combine all types of experiments, the observable features in the power spectrum are in excellent agreement with the WMAP cosmological parameter estimation. This work illustrates the advantages of a model-independent approach to understanding experimental systematics that might affect CMB observations.

COSMOLOGICAL PREDICTIONS FROM THE MISNER BRANE

Within the spirit of five-dimensional gravity in the Randall-Sundrum scenario, in this paper we consider cosmological and gravitational implications induced by forcing the spacetime metric to satisfy a Misner-like symmetry. We first show that in the resulting Misner-brane framework the Friedmann metric for a radiation dominated flat universe and the Schwarzschild or anti-de Sitter black hole metrics are exact solutions on the branes, but the model cannot accommodate any inflationary solution. The horizon and flatness problems can however be solved in Misner-brane cosmology by causal and noncausal communications through the extra dimension between distant regions which are outside the horizon. Based on a semiclassical approximation to the path-integral approach, we have calculated the quantum state of the Misner-brane universe and the quantum perturbations induced on its metric by brane propagation along the fifth direction. We have then considered testable predictions from our model. These include a scale-invariant spectrum of density perturbations whose amplitude can be naturally accommodated to the required value 10-5-10-6, and a power spectrum of CMB anisotropies whose acoustic peaks are at the same sky angles as those predicted by inflationary models, but having much smaller secondary-peak intensities. These predictions seem to be compatible with COBE and recent Boomerang and Maxima measurements.

Observational constraints on dark radiation in brane cosmology

We analyze the observational constraints on brane-world cosmology whereby the universe is described as a three-brane embedded in a five-dimensional anti-de Sitter space. In this brane-universe cosmology, the Friedmann equation is modified by the appearance of extra terms which derive from existence of the extra dimensions. In the present work we concentrate on the “dark radiation” term which diminishes with cosmic scale factor as a −4. We show that, although the observational constraints from primordial abundances allow only a small contribution when this term is positive, a much wider range of negative between the observed primordial 4He and D abundances. We also discuss the possible constraints on this term from the power spectrum of CMB anisotropies in the limit of negligible cosmological perturbation on the brane world. We show that BBN limits the possible contribution from dark radiation just before the e + e − aniihilation epoch to lie between −123% and +11% of the background photon energy density. Combining this with the CMB constraint reduces this range to between −41% and +10.5% at the 2σ confidence level.

Observational constraints on dark radiation in brane cosmology

We analyze the observational constraints on brane-world cosmology whereby the universe is described as a three-brane embedded in a five-dimensional anti--de Sitter space. In this brane-universe cosmology, the Friedmann equation is modified by the appearance of extra terms which derive from the existence of the extra dimensions. In the present work we concentrate on the ``dark radiation'' term which diminishes with the cosmic scale factor as ${a}^{\ensuremath{-}4}.$ We show that, although the observational constraints from primordial abundances allow only a small contribution when this term is positive, a much wider range of negative values is allowed. Furthermore, such a negative contribution can reconcile the tension between the observed primordial ${}^{4}\mathrm{He}$ and D abundances. We also discuss the possible constraints on this term from the power spectrum of CMB anisotropies in the limit of negligible cosmological perturbation on the brane world. We show that BBN limits the possible contribution from dark radiation just before the ${e}^{+}{e}^{\ensuremath{-}}$ annihilation epoch to lie between -123% and +11% of the background photon energy density. Combining this with the CMB constraint reduces this range to between -41% and +10.5% at the $2\ensuremath{\sigma}$ confidence level.

Bayesian joint estimation of non-Gaussianity and the power spectrum

We propose a rigorous, non-perturbative, Bayesian framework which enables one jointly to test Gaussianity and estimate the power spectrum of CMB anisotropies. It makes use of the Hilbert space of an harmonic oscillator to set up an exact likelihood function, dependent on the power spectrum and on a set of parameters ${\ensuremath{\alpha}}_{i},$ which are zero for Gaussian processes. The latter can be expressed as a series of cumulants; indeed they perturbatively reduce to cumulants. However they have the advantage that their variation is essentially unconstrained. Any truncation (i.e., finite set of ${\ensuremath{\alpha}}_{i})$ therefore still produces a proper distribution---something which cannot be said of the only other such tool available, the Edgeworth expansion. We apply our method to Very Small Array (VSA) simulations based on signal Gaussianity, showing that our algorithm is indeed not biased.

Observational test of quantum cosmology

We compute the tensor CMB anisotropy power spectrum for singular and non-singular instantons describing the beginning of an open universe according to the Euclidean no boundary proposal. Singular instantons occur generically, whereas non-singular instantons require more contrived scalar field potentials. For the latter, we consider potentials in which a sharp feature, either negative or positive, is added to a gently sloping potential. In the first case one finds a nearly divergent contribution to the low multipole CMB anisotropy, in conflict with the COBE observations. In the second case the divergence is weaker, but matching the low multipoles forces the added feature to be large and narrow. For singular instantons, there is a better match to the observations, without any such contrivance. The distinction between singular and nonsingular instantons disappears in the limit as the universe becomes flat, but is still observable for densities as high as 0.7 of the critical density.

A two-fluid approximation for calculating the cosmic microwave background anisotropies

view Abstract Citations (91) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Two-Fluid Approximation for Calculating the Cosmic Microwave Background Anisotropies Seljak, Uros Abstract We present a simple, yet accurate approximation for calculating the cosmic microwave background anisotropy power spectrum in adiabatic models. It consists of solving for the evolution of a two-fluid model until the epoch of recombination and then integrating over the sources to obtain the CMB anisotropy power spectrum. The approximation is useful both for a physical understanding of CMB anisotropies, as well as for a quantitative analysis of cosmological models. Comparison with exact calculations shows that the accuracy is typically better than 20 percent over a large range of angles and cosmological models, including those with curvature and cosmological constant. Using this approximation we investigate the dependence of the CMB anisotropies on the cosmological parameters. We identify six dimensionless parameters that uniquely determine the anisotropy power spectrum within our approximation. CMB experiments on different angular scales could in principle provide information on all these parameters. In particular, mapping of the Doppler peaks would allow an independent determination of baryon mass density, matter mass density and Hubble constant. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/187601 arXiv: arXiv:astro-ph/9406050 Bibcode: 1994ApJ...435L..87S Keywords: Anisotropy; Background Radiation; Baryons; Cosmic Rays; Cosmology; Microwaves; Power Spectra; Two Fluid Models; Adiabatic Equations; Approximation; Astronomical Models; Density (Mass/Volume); Evolution (Development); Microwave Spectra; Recombination Reactions; Stellar Radiation; Astrophysics; COSMOLOGY: THEORY; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; Astrophysics E-Print: 12 pages, AAS Latex, ApJL, submitted 1994, preprint MIT-CSR-94-13 full text sources arXiv | ADS |