Radek Stompor

We present a study of unbiased reconstruction of cosmic microwave background (CMB) polarization maps from data collected by modern ground-based observatories. Atmospheric emission is a major source of correlated noise in such experiments, complicating the recovery of faint cosmological signals. We consider estimators that require only minimal assumptions about the properties of the unpolarized atmospheric emission, instead exploiting hardware solutions commonly implemented in modern instruments, such as pairs of orthogonal antennas in each focal plane pixel, interleaving of the antenna orientation from pixel to pixel, and polarization signal modulation via a continuously rotating half-wave plate (HWP). We focus on two techniques: (i) statistical downweighting of low-frequency atmospheric signals and (ii) pair differencing (PD), which involves differencing the signals collected by two detectors in the same focal plane pixel. We compare their performance and contrast them with the idealized case where the atmospheric signal is perfectly known and can be cleanly subtracted. We show that PD can be derived from the maximum likelihood principle under very general assumptions about the atmospheric signal and is therefore optimal in terms of map sensitivity for essentially any such signal. Remarkably, in the absence of instrumental systematics, but with reasonable variations of detector noise properties, PD yields polarized sky maps with noise levels only slightly worse (typically a few percent) than the ideal reference case. While the downweighting method could in principle match or surpass this performance, it requires highly accurate models of the atmospheric signal, which are not readily available. The performance of PD will be affected by instrumental systematics and those leaking the atmospheric signal to the difference time stream may have particularly adverse impact. However, we expect that some of these effects, as shown in the case of gain mismatch, are efficiently mitigated by a continuously rotating HWP and, therefore, that in the context of modern CMB experimental setups PD could provide a competitive, numerically robust, and efficient practical solution for CMB polarization mapmaking without the need for atmospheric modeling.

We report an improved measurement of the degree-scale cosmic microwave background B-mode angular-power spectrum over 670 deg² sky area at 150 GHz with Polarbear. In the original analysis of the data, errors in the angle measurement of the continuously rotating half-wave plate, a polarization modulator, caused significant data loss. By introducing an angle-correction algorithm, the data volume is increased by a factor of 1.8. We report a new analysis using the larger data set. We find the measured B-mode spectrum is consistent with the ΛCDM model with Galactic dust foregrounds. We estimate the contamination of the foreground by cross-correlating our data and Planck 143, 217, and 353 GHz measurements, where its spectrum is modeled as a power law in angular scale and a modified blackbody in frequency. We place an upper limit on the tensor-to-scalar ratio r < 0.33 at 95% confidence level after marginalizing over the foreground parameters.

We present a measurement of the B-mode polarization power spectrum of the cosmic microwave background (CMB) using data taken from 2014 July to 2016 December with the Polarbear experiment. The CMB power spectra are measured using observations at 150 GHz with an instantaneous array sensitivity of on a 670 square degree patch of sky centered at (R.A., decl.) = (+0^h12^m0^s, −59°18′). A continuously rotating half-wave plate is used to modulate polarization and to suppress low-frequency noise. We achieve 32 μK arcmin effective polarization map noise with a knee in sensitivity of ℓ = 90, where the inflationary gravitational-wave signal is expected to peak. The measured B-mode power spectrum is consistent with a ΛCDM lensing and single dust component foreground model over a range of multipoles 50 ≤ ℓ ≤ 600. The data disfavor zero at 2.2σ using this ℓ range of Polarbear data alone. We cross-correlate our data with Planck full mission 143, 217, and 353 GHz frequency maps and find the low-ℓ B-mode power in the combined data set to be consistent with thermal dust emission. We place an upper limit on the tensor-to-scalar ratio r < 0.90 at the 95% confidence level after marginalizing over foregrounds.

We present a measurement of the gravitational lensing deflection power spectrum reconstructed with two seasons of cosmic microwave background polarization data from the Polarbear experiment. Observations were taken at 150 GHz from 2012 to 2014 and surveyed three patches of sky totaling 30 square degrees. We test the consistency of the lensing spectrum with a cold dark matter cosmology and reject the no-lensing hypothesis at a confidence of 10.9σ, including statistical and systematic uncertainties. We observe a value of A _L = 1.33 ± 0.32 (statistical) ±0.02 (systematic) ±0.07 (foreground) using all polarization lensing estimators, which corresponds to a 24% accurate measurement of the lensing amplitude. Compared to the analysis of the first-year data, we have improved the breadth of both the suite of null tests and the error terms included in the estimation of systematic contamination.