Cosmic Microwave Background B-mode Polarization Research Articles

Impact of half-wave plate systematics on the measurement of CMB B-mode polarization

Polarization of the cosmic microwave background (CMB) can help probe the fundamental physics behind cosmic inflation via the measurement of primordial B modes.As this requires exquisite control over instrumental systematics, some next-generation CMB experiments plan to use a rotating half-wave plate (HWP) as polarization modulator.However, the HWP non-idealities, if not properly treated in the analysis, can result in additional systematics.In this paper, we present a simple, semi-analytical end-to-end model to propagate the HWP non-idealities through the macro-steps that make up any CMB experiment (observation of multi-frequency maps, foreground cleaning, and power spectra estimation) and compute the HWP-induced bias on the estimated tensor-to-scalar ratio, r.We find that the effective polarization efficiency of the HWP suppresses the polarization signal, leading to an underestimation of r.Laboratory measurements of the properties of the HWP can be used to calibrate this effect, but we show how gain calibration of the CMB temperature can also be used to partially mitigate it.On the basis of our findings, we present a set of recommendations for the HWP design that can help maximize the benefits of gain calibration.

Disentangling patchy reionization signatures from primordial gravitational waves using CMB E-mode and B-mode polarization

ABSTRACT The detection of large angular scale B mode in the cosmic microwave background (CMB) polarization signal will open a direct window into not only the primary CMB anisotropies caused by the primordial gravitational waves (PGW) originating in the epoch of inflation, but also the secondary anisotropies imprinted during the epoch of cosmic reionization. The existence of patchiness in the electron density during reionization produces a unique distortion in the CMB B-mode polarization, which can be distinguished from the PGW signal with the aid of spatial frequency modes. In this work, we employ an EB estimator by combining E-mode and B-mode polarization for the τ power spectrum signal generated in a photon-conserving seminumerical reionization model called SCRIPT. We developed a Bayesian framework for the joint detection of the PGW and reionization signal from CMB observations and show the efficacy of this technique for upcoming CMB experiments. We find that, for our model, the τ power spectrum signal effectively tracks the inhomogeneous electron density field, allowing for robust constraints on the patchy B-mode signal. Further, our results indicate that employing the EB estimator for the τ signal will facilitate ground-based CMB-S4 to detect the patchy B-mode signal at approximately ≥2σ confidence level, while observations with space-based PICO will improve this detection to ≥3σ going as high as ≥7σ for extreme reionization models. These findings not only highlight the future potential of these experiments to provide an improved picture of the reionization process but also have important implications towards an unbiased measurement of r.

Mitigating Cosmic Microwave Background Shadow Degradation of Tensor-to-scalar Ratio Measurements through Map-based Studies

It has been pointed out that the spurious cosmic microwave background (CMB) B-mode polarization signals caused by the absorption of the CMB monopole component due to the Galactic interstellar matter, called the CMB shadow, degrade the accuracy of detecting the CMB B-mode polarization signals imprinted by primordial gravitational waves. We have made a realistic estimation using simulated sky maps of how the CMB shadow affects forthcoming high-precision CMB B-mode experiments for the first time. The delta-map method, an internal template method taking into account the first-order spatial variation of foregrounds’ spectral parameters, is applied as a foreground-removal method. We show that if the CMB shadow effects are not taken into account in the foreground-removal process, future observations would lead to the false detection of the CMB B-mode polarization signals originating from primordial gravitational waves. We also show that the effect of the CMB shadow can be mitigated by our revised delta-map method to target the CMB B-mode polarization signals at the level of tensor-to-scalar ratio r = 0.001.

Unified approach to secondary effects on the CMB B-mode polarization

We develop a systematic and unified approach to estimate all possible secondary (i.e. non-primordial) nonlinear effects to the cosmic microwave background (CMB) polarization, named curve-of-sight integration approach.In this approach, the Boltzmann equation for polarized photons is rewritten in a line-of-sight integral along an exact geodesic in the perturbed universe,rather than a geodesic in the background universe used in the linear-order CMB calculation.This approach resolves the difficulty to solve the Boltzmann hierarchy with the nonlinear gravitational effects in the photon free-streaming regime and thus unifies the standard remapping approach for CMB lensing into the direct approach solving the Boltzmann equation for the nonlinear collisional effects.In this paper, we derive formulae that: (i) include all the nonlinear effects; (ii) can treat extended sources such as the contributions after the reionization.It offers a solid framework to discuss possible systematics in the standard estimation of CMB lensing by the remapping approach.As an explicit demonstration,we estimate the secondary B-mode power spectrum induced by all foreground gravitational effects:lensing, redshift, time-delay, emission-angle, and polarization-rotation effects.We define these effects properly so that they do not have any overlap, also without overlooking any effect.Then, we show that these effects only give corrections of the order of 0.001­-0.01% to the standard lensing-induced B-mode power spectrum in the concordance Λ cold dark matter model.Our result confirms the reliability of using the remapping approach in upcoming CMB experiments aiming to detect the primordial gravitational waves with the tensor-to-scalar ratio of r ∼ 10-3.

Integrated Electrical Properties of the Frequency Multiplexed Cryogenic Readout System for Polarbear/Simons Array

Polarbear/Simons Array is a cosmic microwave background (CMB) polarization experiment, with science goals including a deep search for CMB B-mode polarization created by inflationary gravitational waves, and characterization of the CMB B-mode signal from gravitational lensing. When completed, Simons Array will have over 20,000 superconducting transition-edge sensor bolometers, cooled to 300 mK with closed-cycle cryogenics. This significant increase in detectors and sensitivity is enabled by advancements in frequency multiplexed readout. The detectors are read out with DfMux digital frequency-domain multiplexing, with 40 channels read out by each SQUID array, with frequency channels between 1 and 5 MHz defined by an inductor and capacitor in series with each detector. After the system was completed and characterized for Polarbear-2a, modifications were made that further improved performance for Polarbear-2b. We present the characterization of the integrated cryogenic readout system for Polarbear-2a and Polarbear-2b, and comparison of properties including stray impedance and frequency scatter.

Statistically-anisotropic tensor bispectrum from inflation

We develop a possibility of generating tensor non-Gaussianity in a kind of anisotropic inflation, where a (1) gauge field is kinetically coupled to a spectator scalar field.Owing to this coupling, the coherent mode of the electric field appears and softly breaks the isotropy of the Universe.We compute the bispectrum of linearly-polarized tensor perturbations sourced by the gauge field and find that it is strongly red-tiltedand has distinctive statistical anisotropies including higher-order multipole moments.Interestingly, the tensor bispectra with the specific combinations of linear polarization modes are dominant, and their amplitudes depend on the different sets of multipole moments.This new type of statistically-anisotropic tensor non-Gaussianity can be potentially testable with the upcoming cosmic microwave background B-mode polarization experiments.

CMB Shadows: The Effect of Interstellar Extinction on Cosmic Microwave Background Polarization and Temperature Anisotropy

Abstract We evaluate the degradation of the accuracy of the component separation between the cosmic microwave background (CMB) and foreground components caused by neglect of absorption of the CMB’s monopole component by the galactic interstellar matter. The amplitude of the temperature anisotropy caused by the CMB shadow, due to dust components, is about 1 μK. This value is comparable to the required noise level necessary to probe non-Gaussianity studies with upcoming CMB experiments. In addition, the amplitude of the polarization caused by the CMB shadow due to dust is comparable to or larger than the rms value of the CMB B-mode polarization, imprinted by primordial gravitational waves. We show that applying a single-power-law model as the dust spectrum to observed multifrequency data introduces systematic errors, which are comparable to or larger than the required noise level for forthcoming CMB B-mode polarization experiments. Deducing the intrinsic spectrum of dust emission from the submillimeter wave band data reduces the systematic error to below the required noise level. However, this method requires dust temperature measurements with an accuracy of better than a few percent. We conclude that the CMB shadow due to dust must be considered in future CMB missions for achieving their targeted sensitivity. Our results will be important to detect the primordial CMB B-mode polarization, with the amplitude of the tensor-to-scalar ratio of r = 10−3.

Searching for primordial magnetic fields with CMB B-modes

Was the primordial universe magnetized? The answer to this question would help explain the origin of micro-Gauss strength magnetic fields observed in galaxies. It is also of fundamental importance in developing a complete theory of the early universe. While there can be other signatures of cosmological magnetic fields, a signature in the cosmic microwave background (CMB) would prove their primordial origin. The B-mode polarization of CMB is particularly promising in this regard because there are relatively few other sources of B-modes, and because the vortical modes sourced by the primordial magnetic field (PMF) survive diffusion damping up to a small fraction of the Silk length. At present, the Planck temperature and polarization spectra combined with the B-mode spectrum measured by the South Pole Telescope (SPT) constrain the PMF strength to be no more than ∼1 nano-Gauss (nG). Because of the quartic scaling of the CMB anisotropy spectra with the PMF strength, this bound will not change by much even with the significantly better measurements of the B-mode spectrum by the Stage III and Stage IV CMB experiments. On the other hand, tightening the bound well below the 1 nG threshold would rule out the purely primordial origin (requiring no dynamo action) of galactic fields. Considering Faraday rotation, which converts some of the E-modes into B-modes and scales linearly with the field strength, will help to achieve this goal. As we demonstrate, the upcoming experiments, such as SPT-3G and the Simons Observatory, will be sensitive to fields of ∼0.5 nG strength thanks to the mode-coupling signature induced by Faraday rotation. A future Stage IV ground based experiment or a space probe will be capable of probing fields below 0.1 nG, and would detect a scale-invariant PMF of 0.2 nG strength without de-lensing or subtracting the galactic rotation measure.

Impact of polarized foregrounds on LSPE-SWIPE observations

A first measurement of Cosmic Microwave Background B-mode polarization on large scales could provide a convincing confirmation of the existence of a primordial background of gravitational waves as predicted in the inflation scenario. A major obstacle to observe B-modes is represented by polarized foreground contamination from our Galaxy. In particular, thermal dust and synchrotron emission dominate over the primordial signal at high and low frequencies, respectively. Several experiments have been designed to observe B-mode polarization. Here, we focus on the forthcoming LSPE-SWIPE balloon experiment, devoted to the accurate observation of large scale CMB polarization, and present preliminary forecasts on the impact of foreground contamination on LSPE-SWIPE observations. Using the last release of Planck foreground maps as templates, we estimate the amplitude of dust and synchrotron emission in the sky region and at the frequency channels of interest for LSPE-SWIPE. Furthermore, we investigate the generation of polarization-optimized Galactic masks and we give preliminary indications on the requirements of component separation methods.

A Measurement of the Cosmic Microwave Background B-mode Polarization Power Spectrum at Subdegree Scales from Two Years of polarbear Data

Abstract We report an improved measurement of the cosmic microwave background B-mode polarization power spectrum with the Polarbear experiment at 150 GHz. By adding new data collected during the second season of observations (2013–2014) to re-analyzed data from the first season (2012–2013), we have reduced twofold the band-power uncertainties. The band powers are reported over angular multipoles , where the dominant B-mode signal is expected to be due to the gravitational lensing of E-modes. We reject the null hypothesis of no B-mode polarization at a confidence of 3.1σ including both statistical and systematic uncertainties. We test the consistency of the measured B-modes with the Λ Cold Dark Matter (ΛCDM) framework by fitting for a single lensing amplitude parameter A L relative to the Planck 2015 best-fit model prediction. We obtain ± 0.14(foreground) ± 0.04(multi), where is the fiducial ΛCDM value.

Axion dark matter induced cosmic microwave backgroundBmodes

It was known that isocurvature perturbation of a nearly massless cosmological axion field can lead to rotation of E-mode polarization into B-mode polarization in the cosmic microwave background (CMB) by the presence of a parity violating coupling of the field to the topological density of electromagnetism, resulting in a phenomenon known as anisotropic cosmic birefringence. In this Letter, we propose a new source of anisotropic cosmic birefringence induced by dark matter adiabatic density perturbation. If dark matter is ultralight axions that carry a coupling to photon, its adiabatic density fluctuations will induce anisotropic cosmic birefringence with a blue-tilted rotation power spectrum, thus generating CMB B-mode polarization on sub-degree angular scales. Using current POLARBEAR and SPTPol B-mode polarization data, we derive a constraint on the axion–photon coupling strength (β) and the axion mass (m), β2(10−22eV∕m)2<8×1015. It is shown that the birefringence B modes can dominate over CMB lensing B modes at high l, manifesting as an excess power for l>1500 in future CMB lensing B-mode searches. In addition, we derive the lensing–rotation cross correlation that can be a potential test to the present model.

Probing the statistical properties of CMB B-mode polarization through Minkowski functionals

The detection of the magnetic type B-mode polarization is the main goal of future cosmic microwave background (CMB) experiments. In the standard model, the B-mode map is a strong non-gaussian field due to the CMB lensing component. Besides the two-point correlation function, the other statistics are also very important to dig the information of the polarization map. In this paper, we employ the Minkowski functionals to study the morphological properties of the lensed B-mode maps. We find that the deviations from Gaussianity are very significant for both full and partial-sky surveys. As an application of the analysis, we investigate the morphological imprints of the foreground residuals in the B-mode map. We find that even for very tiny foreground residuals, the effects on the map can be detected by the Minkowski functional analysis. Therefore, it provides a complementary way to investigate the foreground contaminations in the CMB studies.

Simple inflationary models in Gauss–Bonnet brane-world cosmology

In light of the recent Planck 2015 results for the measurement of the cosmic microwave background (CMB) anisotropy, we study simple inflationary models in the context of the Gauss–Bonnet (GB) brane-world cosmology. The brane-world cosmological effect modifies the power spectra of scalar and tensor perturbations generated by inflation and causes a dramatic change for the inflationary predictions of the spectral index (ns) and the tensor-to-scalar ratio (r) from those obtained in the standard cosmology. In particular, the predicted r values in the inflationary models favored by the Planck 2015 results are suppressed due to the GB brane-world cosmological effect, which is in sharp contrast with inflationary scenario in the Randall–Sundrum brane-world cosmology, where the r values are enhanced. Hence, these two brane-world cosmological scenarios are distinguishable. With the dramatic change of the inflationary predictions, the inflationary scenario in the GB brane-world cosmology can be tested by more precise measurements of ns and future observations of the CMB B-mode polarization.

Sensitivity and foreground modelling for large-scale cosmic microwave background B-mode polarization satellite missions

The measurement of the large-scale B-mode polarization in the cosmic microwave background (CMB) is a fundamental goal of future CMB experiments. However, because of unprecedented sensitivity, future CMB experiments will be much more sensitive to any imperfect modelling of the Galactic foreground polarization in the reconstruction of the primordial B-mode signal. We compare the sensitivity to B-modes of different concepts of CMB satellite missions (LiteBIRD, COrE, COrE+, PRISM, EPIC, PIXIE) in the presence of Galactic foregrounds. In particular, we quantify the impact on the tensor-to-scalar parameter of incorrect foreground modelling in the component separation process. Using Bayesian fitting and Gibbs sampling, we perform the separation of the CMB and Galactic foreground B-modes. The recovered CMB B-mode power spectrum is used to compute the likelihood distribution of the tensor-to-scalar ratio. We focus the analysis to the very large angular scales that can be probed only by CMB space missions, i.e. the Reionization bump, where primordial B-modes dominate over spurious B-modes induced by gravitational lensing. We find that fitting a single modified blackbody component for thermal dust where the "real" sky consists of two dust components strongly bias the estimation of the tensor-to-scalar ratio by more than 5{\sigma} for the most sensitive experiments. Neglecting in the parametric model the curvature of the synchrotron spectral index may bias the estimated tensor-to-scalar ratio by more than 1{\sigma}. For sensitive CMB experiments, omitting in the foreground modelling a 1% polarized spinning dust component may induce a non-negligible bias in the estimated tensor-to-scalar ratio.

BFORE: The B-mode Foreground Experiment

The B-mode Foreground Experiment (BFORE) is a proposed NASA balloon project designed to make optimal use of the sub-orbital platform by concentrating on three dust foreground bands (270, 350, and 600 GHz) that complement ground-based cosmic microwave background (CMB) programs. BFORE will survey ~1/4 of the sky with 1.7 - 3.7 arcminute resolution, enabling precise characterization of the Galactic dust that now limits constraints on inflation from CMB B-mode polarization measurements. In addition, BFORE's combination of frequency coverage, large survey area, and angular resolution enables science far beyond the critical goal of measuring foregrounds. BFORE will constrain the velocities of thousands of galaxy clusters, provide a new window on the cosmic infrared background, and probe magnetic fields in the interstellar medium. We review the BFORE science case, timeline, and instrument design, which is based on a compact off-axis telescope coupled to >10,000 superconducting detectors.

A MEASUREMENT OF THE COSMIC MICROWAVE BACKGROUND B-MODE POLARIZATION WITH POLARBEAR

POLARBEAR is a ground-based experiment located in the Atacama desert of northern Chile. The experiment is designed to measure the Cosmic Microwave Background B-mode polarization at several arcminute resolution. The CMB B-mode polarization on degree angular scales is a unique signature of primordial gravitational waves from cosmic inflation and B-mode signal on sub-degree scales is induced by the gravitational lensing from large-scale structure. Science observations began in early 2012 with an array of 1.274 polarization sensitive antenna-couple Transition Edge Sensor (TES) bolometers at 150 GHz. We published the first CMB-only measurement of the B-mode polarization on sub-degree scales induced by gravitational lensing in December 2013 followed by the first measurement of the B-mode power spectrum on those scales in March 2014. In this proceedings, we review the physics of CMB B-modes and then describe the Polarbear experiment, observations, and recent results.

NEW CONSTRAINTS ON COSMIC POLARIZATION ROTATION FROM THE ACTPol COSMIC MICROWAVE BACKGROUND B-MODE POLARIZATION OBSERVATION AND THE BICEP2 CONSTRAINT UPDATE

Recently ACTPol has measured the cosmic microwave background (CMB) B-mode and E-mode polarizations and obtained TE, EE, BB, TB and EB power spectra in the multipole range 225-8725. In our previous paper (Ap. J. 792 (2014) 35 [Paper I]), we have analyzed jointly the results of three experiments on the CMB B-mode polarization -- SPTpol, POLARBEAR and BICEP2 to include in the model, in addition to the gravitational lensing and the inflationary gravitational waves components, also the fluctuation effects induced by the cosmic polarization rotation (CPR), if it exists within the upper limits at the time. In this paper, we fit both the mean CPR angle <{\alpha}> and its fluctuation <{\delta}{\alpha}2> from the new ACTPol data, and update our fitting of CPR fluctuations using BICEP2 data taking the new Planck dust measurement results into consideration. We follow the method of Paper I. The mean CPR angle is constrained from the EB correlation power spectra to |<{\alpha}>| < 14 mrad (0.8{\deg}) and the fluctuation (rms) is constrained from the BB correlation power spectra to <{\delta}{\alpha}2>1/2 < 29.3 mrad (1.68{\deg}). Assuming that the polarization angle of Tau A does not change from 89.2 to 146 GHz, the ACTPol data give <{\alpha}> = 1.0 {\pm} 0.63{\deg}. These results suggest that the inclusion of the present ACTPol data is consistent with no CPR detection. With the new Planck dust measurement, we update our fits of the BICEP2 CPR fluctuation constraint to be 32.8 mrad (1.88{\deg}). The joint ACTpol-BICEP2-POLARBEAR CPR fluctuation constraint is 23.7 mrad (1.36{\deg}).

Cosmic birefringence fluctuations and cosmic microwave background B-mode polarization

Recently, BICEP2 measurements of the cosmic microwave background (CMB) B-mode polarization has indicated the presence of primordial gravitational waves at degree angular scales, inferring the tensor-to-scalar ratio of r=0.2 and a running scalar spectral index, provided that dust contamination is low. In this Letter, we show that the existence of the fluctuations of cosmological birefringence can give rise to CMB B-mode polarization that fits BICEP2 data with r<0.11 and no running of the scalar spectral index. When dust contribution is taken into account, we derive an upper limit on the cosmological birefringence, Aβ2<0.0075, where A is the amplitude of birefringence fluctuations that couple to electromagnetism with a coupling strength β.

Neutrino masses from CMB B-mode polarization and cosmic growth rate

Constraints on neutrino masses are estimated based on future observations of the cosmic microwave background (CMB), which includes the B-mode polarization produced by CMB lensing from the Planck satellite, and the growth rate of cosmic structure from the Euclid redshift survey by using the Markov–Chain Monte-Carlo (MCMC) method. The error in the bound on the total neutrino mass is estimated to be Δ ∑ mν = 0.075 eV with a 68% confidence level. By using the growth rate rather than the galaxy power spectrum, accurate constraints are obtained, since the growth rate is less influenced by the uncertainty regarding galaxy bias than by the galaxy power spectrum.

BICEP2, Planck, spinorial space-time, pre-Big Bang.

The field of Cosmology is currently undergoing a positive and constructive crisis. Controversies concerning inflation are not really new. But after the 2013-2014 Planck and BICEP2 announcements, and the more recent joint analysis by Planck, BICEP2 and the Keck Array (PBKA), the basic issues can involve more direct links between the Mathematical Physics aspects of cosmological patterns and the interpretation of experimental results. Open questions and new ideas on the foundations of Cosmology can emerge, while future experimental and observational programs look very promising. The BICEP2 result reporting an excess of B-mode polarization signal of the cosmic microwave background (CMB) radiation was initially presented as a signature of primordial gravitational waves from cosmic inflation. But polarized dust emission can be at the origin of such a signal, and the evidence claimed by BICEP2 is no longer secure after the PBKA analysis. Furthermore, even assuming that significant CMB B-mode polarization has indeed been generated by the early Universe, its theoretical and cosmological interpretation would be far from obvious. Inflationary gravitational waves are not the only possible source of primordial CMB B-modes. Alternative cosmologies such as pre-Big Bang patterns and the spinorial space-time (SST) we introduced in 1996-97 can naturally produce this polarization. Furthermore, the SST automatically generates for each comoving observer a local privileged space direction (PSD) whose existence may have been confirmed by Planck data. If such a PSD exists, vector perturbations have most likely been strong in the early Universe and may have produced CMB B-modes. Pre-Big Bang cosmologies can also generate gravitational waves in the early Universe without inflation. After briefly describing detectors devoted to the study of the CMB polarization, we discuss the situation emerging from BICEP2 results, Planck results and the PBKA analysis. In particular, we further analyze possible alternatives to the inflationary interpretation of a primordial B-mode polarization of cosmic microwave background radiation.