The unimpeded relativistic propagation of cosmological neutrinos prior to recombination of the baryon-photon plasma alters gravitational potentials and therefore the details of the time-dependent ...gravitational driving of acoustic oscillations. We report here a first detection of the resulting shifts in the temporal phase of the oscillations, which we infer from their signature in the cosmic microwave background temperature power spectrum.
One of the major targets for next-generation cosmic microwave background (CMB) experiments is the detection of the primordial B-mode signal. Planning is under way for Stage-IV experiments that are ...projected to have instrumental noise small enough to make lensing and foregrounds the dominant source of uncertainty for estimating the tensor-to-scalar ratio r from polarization maps. This makes delensing a crucial part of future CMB polarization science. In this paper we present a likelihood method for estimating the tensor-to-scalar ratio r from CMB polarization observations, which combines the benefits of a full-scale likelihood approach with the tractability of the quadratic delensing technique. This method is a pixel space, all order likelihood analysis of the quadratic delensed B modes, and it essentially builds upon the quadratic delenser by taking into account all order lensing and pixel space anomalies. Its tractability relies on a crucial factorization of the pixel space covariance matrix of the polarization observations which allows one to compute the full Gaussian approximate likelihood profile, as a function of r, at the same computational cost of a single likelihood evaluation.
We study the prospects for extracting detailed statistical properties of the neutral hydrogen distribution during the era of reionization using the brightness temperature fluctuations from redshifted ...21 cm line emission. Detection of this signal is complicated by contamination from foreground sources such as diffuse Galactic synchrotron and free-free emission at low radio frequencies, extragalactic free-free emission from ionized regions, and radio point sources. We model these foregrounds to determine the extent to which 21 cm fluctuations can be detected with upcoming experiments. We find that not only the level of correlation from one frequency to another but also the functional form of the foreground correlations has a substantial impact on foreground removal. We calculate how well the angular power spectra of the 21 cm fluctuations can be determined. We also show that the large-scale bias of the neutral hydrogen gas distribution with respect to the density field can be determined with high precision and used to distinguish between different reionization histories.
CMB-S4 and the hemispherical variance anomaly O'Dwyer, Márcio; Copi, Craig J; Knox, Lloyd ...
Monthly Notices of the Royal Astronomical Society,
09/2017, Volume:
470, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
Cosmic microwave background (CMB) full-sky temperature data show a hemispherical asymmetry in power nearly aligned with the Ecliptic. In real space, this anomaly can be quantified by the ...temperature variance in the Northern and Southern Ecliptic hemispheres, with the Northern hemisphere displaying an anomalously low variance while the Southern hemisphere appears unremarkable consistent with expectations from the best-fitting theory, Lambda Cold Dark Matter (ΛCDM). While this is a well-established result in temperature, the low signal-to-noise ratio in current polarization data prevents a similar comparison. This will change with a proposed ground-based CMB experiment, CMB-S4. With that in mind, we generate realizations of polarization maps constrained by the temperature data and predict the distribution of the hemispherical variance in polarization considering two different sky coverage scenarios possible in CMB-S4: full Ecliptic north coverage and just the portion of the North that can be observed from a ground-based telescope at the high Chilean Atacama plateau. We find that even in the set of realizations constrained by the temperature data, the low Northern hemisphere variance observed in temperature is not expected in polarization. Therefore, observing an anomalously low variance in polarization would make the hypothesis that the temperature anomaly is simply a statistical fluke more unlikely and thus increase the motivation for physical explanations. We show, within ΛCDM, how variance measurements in both sky coverage scenarios are related. We find that the variance makes for a good statistic in cases where the sky coverage is limited, however, full northern coverage is still preferable.
We show that the polarization of the cosmic microwave background can be used to detect gravity waves from inflation if the energy scale of inflation is above 2x10(15) GeV. These gravity waves ...generate polarization patterns with a curl, whereas (to first order in perturbation theory) density perturbations do not. The limiting "noise" arises from the second-order generation of curl from density perturbations, or rather residuals from its subtraction. We calculate optimal sky coverage and detectability limits as a function of detector sensitivity and observing time.
We investigate how well the redshift distributions of galaxies sorted into photometric redshift bins can be determined from the galaxy angular two-point correlation functions. We find that the ...uncertainty in the reconstructed redshift distributions depends critically on the number of parameters used in each redshift bin and the range of angular scales used, but not on the number of photometric redshift bins. Using six parameters for each photometric redshift bin, and restricting ourselves to angular scales over which the galaxy number counts are normally distributed, we find that errors in the reconstructed redshift distributions are large; i.e., they would be the dominant source of uncertainty in cosmological parameters estimated from otherwise ideal weak lensing or baryon acoustic oscillation data. However, either by reducing the number of free parameters in each redshift bin or by (unjustifiably) applying our Gaussian analysis into the non-Gaussian regime, we find that the correlation functions can be used to reconstruct the redshift distributions with moderate precision; e.g., with mean redshifts determined to 60.01. We also find that dividing the galaxies into two spectral types, thereby doubling the number of redshift distribution parameters, can result in a reduction in the errors in the combined redshift distributions.
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