We study systematic effects from half-wave plates (HWPs) for cosmic microwave background (CMB) experiments using full-sky time-domain beam convolution simulations. Using an optical model for a fiducial spaceborne two-lens refractor telescope, we investigate how different HWP configurations optimized for dichroic detectors centred at 95 and 150 GHz impact the reconstruction of primordial B-mode polarization. We pay particular attention to possible biases arising from the interaction of frequency dependent HWP non-idealities with polarized Galactic dust emission and the interaction between the HWP and the instrumental beam. To produce these simulations, we have extended the capabilities of the publicly available beamconv code. To our knowledge, we produce the first time-domain simulations that include both HWP non-idealities and realistic full-sky beam convolution. Our analysis shows how certain achromatic HWP configurations produce significant systematic polarization angle offsets that vary for sky components with different frequency dependence. Our analysis also demonstrates that once we account for interactions with HWPs, realistic beam models with non-negligible cross-polarization and sidelobes will cause significant B-mode residuals that will have to be extensively modelled in some cases.
Robust CMB polarisation mapmaking with a rotating half-wave plate
Université Paris Cité, CNRS, Astroparticule et Cosmologie（巴黎西岱大学，法国国家科学研究中心，粒子与宇宙学）；Jodrell Bank Centre for Astrophysics, University of Manchester（曼彻斯特大学，天体物理学乔德雷尔银行中心）
Next generation cosmic microwave background (CMB) polarization anisotropy measurements will feature focal plane arrays with more than 600 millimeter-wave detectors. We make use of high-resolution photolithography and wafer-scale etch tools to build planar arrays of corrugated platelet feeds in silicon with highly symmetric beams, low cross-polarization and low side lobes. A compact Au-plated corrugated Si feed designed for 150 GHz operation exhibited performance equivalent to that of electroformed feeds: ~-0.2 dB insertion loss, <-20 dB return loss from 120 GHz to 170 GHz, <-25 dB side lobes a…
We evaluate the modulation of Cosmic Microwave Background (CMB) polarization using a rapidly-rotating, half-wave plate (HWP) on the Atacama B-Mode Search (ABS). After demodulating the time-ordered-data (TOD), we find a significant reduction of atmospheric fluctuations. The demodulated TOD is stable on time scales of 500-1000 seconds, corresponding to frequencies of 1-2 mHz. This facilitates recovery of cosmological information at large angular scales, which are typically available only from balloon-borne or satellite experiments. This technique also achieves a sensitive measurement of celestia…
We describe the development of an ambient-temperature continuously-rotating half-wave plate (HWP) for study of the Cosmic Microwave Background (CMB) polarization by the POLARBEAR-2 (PB2) experiment. Rapid polarization modulation suppresses 1/f noise due to unpolarized atmospheric turbulence and improves sensitivity to degree-angular-scale CMB fluctuations where the inflationary gravitational wave signal is thought to exist. A HWP modulator rotates the input polarization signal and therefore allows a single polarimeter to measure both linear polarization states, eliminating systematic errors as…
Polarization of the cosmic microwave background (CMB) can probe new parity-violating physics such as cosmic birefringence (CB), which requires exquisite control over instrumental systematics. The non-idealities of the half-wave plate (HWP) represent a source of systematics when used as a polarization modulator. We study their impact on the CMB angular power spectra, which is partially degenerate with CB and miscalibration of the polarization angle. We use full-sky beam convolution simulations including HWP to generate mock noiseless time-ordered data, process them through a bin averaging map-m…
The search for the B-mode polarization of Cosmic Microwave Background (CMB) is the new frontier of observational Cosmology. A B-mode detection would give an ultimate confirmation to the existence of a primordial Gravitational Wave (GW) background as predicted in the inflationary scenario. Several experiments have been designed or planned to observe B-modes. In this work we focus on the forthcoming Large Scale Polarization Explorer (LSPE) experiment, that will be devoted to the accurate measurement of CMB polarization at large angular scales. LSPE consists of a balloon-borne bolometric instrume…
Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Scientific Computing and Imaging Institute, University of Utah（犹他大学科学计算与影像研究所）
The cosmic microwave background (CMB) is a significant source of knowledge about the origin and evolution of our universe. However, observations of the CMB are contaminated by foreground emissions, obscuring the CMB signal and reducing its efficacy in constraining cosmological parameters. We employ deep learning as a data-driven approach to CMB cleaning from multi-frequency full-sky maps. In particular, we develop a graph-based Bayesian convolutional neural network based on the U-Net architecture that predicts cleaned CMB with pixel-wise uncertainty estimates. We demonstrate the potential of t…
Component separation is the process with which emission sources in astrophysical maps are generally extracted by taking multi-frequency information into account. It is crucial to develop more reliable methods for component separation for future CMB experiments. We aim to develop a new method based on fully convolutional neural networks called the Cosmic microwave background Extraction Neural Network (CENN) in order to extract the CMB signal in total intensity. The frequencies used are the Planck channels 143, 217 and 353 GHz. We validate the network at all sky, and at three latitude intervals:…
Half-wave-plate non idealities propagated to component separated CMB $B$-modes
Université Paris Cité（巴黎西岱大学）；CNRS, Astroparticule et Cosmologie（法国国家科学研究中心，粒子与宇宙学）；Jodrell Bank Centre for Astrophysics, University of Manchester（曼彻斯特大学，约德尔银行天体物理学中心）
We describe the design of a cryogenic rotation stage (CRS) for use with the cryogenic half-wave plate (CHWP) polarization modulator on the POLARBEAR-2b and POLARBEAR-2c (PB2b/c) cosmic microwave background (CMB) experiments, the second and third installments of the Simons Array. Rapid modulation of the CMB polarization signal using a CHWP suppresses 1/f contamination due to atmospheric turbulence and allows a single polarimeter to measure both polarization states, mitigating systematic effects that arise when differencing orthogonal detectors. To modulate the full detector array while avoiding…
Polarimetry using a half-wave plate (HWP) modulator provides the strong tools to avoid a detector 1/f noise and instrument-originated spurious polarization systematic effects. While the Pancharatnam achromatic HWP (AHWP) is commonly used for an application that needs a broadband frequency coverage, this technique introduces a frequency-dependent polarization angle rotation. In this paper we propose a new technique to mitigate this effect by introducing a second set of an AHWP. One rotational and one stationary set of AHWPs achieve a broadband coverage of modulation efficiency without the frequ…
Spider is a balloon-borne array of six telescopes that will observe the Cosmic Microwave Background. The 2624 antenna-coupled bolometers in the instrument will make a polarization map of the CMB with approximately one-half degree resolution at 145 GHz. Polarization modulation is achieved via a cryogenic sapphire half-wave plate (HWP) skyward of the primary optic. We have measured millimeter-wave transmission spectra of the sapphire at room and cryogenic temperatures. The spectra are consistent with our physical optics model, and the data gives excellent measurements of the indices of A-cut sap…
Precise measurement of the angular power spectrum of the Cosmic Microwave Background (CMB) temperature and polarization anisotropy can tightly constrain many cosmological models and parameters. However, accurate measurements can only be realized in practice provided all major systematic effects have been taken into account. Beam asymmetry, coupled with the scan strategy, is a major source of systematic error in scanning CMB experiments such as Planck, the focus of our current interest. We envision Monte Carlo methods to rigorously study and account for the systematic effect of beams in CMB ana…
We present an exact expression for the $1/f$ contribution to the noise of the CMB temperature and polarization maps for a survey in which the scan pattern is isotropic. The result for polarization applies likewise to surveys with and without a rotating half-wave plate. A representative range of survey parameters is explored and implications for the design and optimization of future surveys are discussed. These results are most directly applicable to space-based surveys, which afford considerable freedom in the choice of the scan pattern on the celestial sphere. We discuss the applicability of …
The Atacama B-mode Search (ABS) experiment is a 145 GHz polarimeter designed to measure the B-mode polarization of the Cosmic Microwave Background (CMB) at large angular scales. The ABS instrument will ship to the Atacama Desert of Chile fully tested and ready to observe in 2010. ABS will image large-angular-scale CMB polarization anisotropies onto a focal plane of 240 feedhorn-coupled, transition-edge sensor (TES) polarimeters, using a cryogenic crossed-Dragone design. The ABS detectors, which are fabricated at NIST, use orthomode transducers to couple orthogonal polarizations of incoming rad…
We introduce the concept of compressed convolution, a technique to convolve a given data set with a large number of non-orthogonal kernels. In typical applications our technique drastically reduces the effective number of computations. The new method is applicable to convolutions with symmetric and asymmetric kernels and can be easily controlled for an optimal trade-off between speed and accuracy. It is based on linear compression of the collection of kernels into a small number of coefficients in an optimal eigenbasis. The final result can then be decompressed in constant time for each desire…
Deep Learning for CMB Foreground Removal and Beam Deconvolution: A U-Net GAN Approach
School of Physical Sciences, Indian Institute of Technology Mandi（印度技术学院曼迪分校物理科学学院）；Department of Physics, Indian Institute of Technology Delhi（印度技术学院德里分校物理系）；Oridigm Inc.（Oridigm公司）
With the temperature power spectrum of the cosmic microwave background (CMB) at least four orders of magnitude larger than the B-mode polarisation power spectrum, any instrumental imperfections that couple temperature to polarisation must be carefully controlled and/or removed. Here we present two new map-making algorithms that can create polarisation maps that are clean of temperature-to-polarisation leakage systematics due to differential gain and pointing between a detector pair. Where a half wave plate is used, we show that the spin-2 systematic due to differential ellipticity can also by …
The Atacama B-Mode Search (ABS) instrument is a cryogenic ($\sim$10 K) crossed-Dragone telescope located at an elevation of 5190 m in the Atacama Desert in Chile that observed for three seasons between February 2012 and October 2014. ABS observed the Cosmic Microwave Background (CMB) at large angular scales ($40<\ell<500$) to limit the B-mode polarization spectrum around the primordial B-mode peak from inflationary gravity waves at $\ell \sim100$. The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers. They are coupled to orthogonal polarizations from a planar ortho-mode t…
With a single training image and using wavelet phase harmonic augmentation, we present polarized Cosmic Microwave Background (CMB) foreground marginalization in a high-dimensional likelihood-free (Bayesian) framework. We demonstrate robust foreground removal using only a single frequency of simulated data for a BICEP-like sky patch. Using Moment Networks we estimate the pixel-level posterior probability for the underlying {E,B} signal and validate the statistical model with a quantile-type test using the estimated marginal posterior moments. The Moment Networks use a hierarchy of U-Net convolu…
We study the propagation of a specific class of instrumental systematics to the reconstruction of the B-mode power spectrum of the cosmic microwave background (CMB). We focus on the non-idealities of the half-wave plate (HWP), a polarization modulator that is to be deployed by future CMB experiments, such as the phase-A satellite mission LiteBIRD. We study the effects of non-ideal HWP properties, such as transmittance, phase shift, and cross-polarization. To this end, we developed a simple, yet stand-alone end-to-end simulation pipeline adapted to LiteBIRD. We analyzed the effects of a possibl…
(Abridged) Despite the great success of precision cosmology, cosmologists cannot fully explain the initial conditions of the Universe. Inflation, an exponential expansion in the first 10^-36s, is a promising potential explanation. A generic prediction of inflation is odd-parity (B-mode) polarization in the cosmic microwave background (CMB). The Q/U Imaging ExperimenT (QUIET) aimed to limit or detect this polarization. We built a coherent pseudo-correlation microwave polarimeter. An array of mass-produced modules populated the focal plane of a 1.4m telescope. Each module had a sensitivity to po…
Point Source (PS) detection is an important issue for future Cosmic Microwave Background (CMB) experiments since they are one of the main contaminants to the recovery of CMB signal at small scales. Improving its multifrequency detection would allow to take into account valuable information otherwise neglected when extracting PS using a channel-by-channel approach. We develop a method based on Neural Networks (NNs) to detect PS in multifrequency realistic simulations and compare its performance against one of the most popular methods, the matrix filters. The frequencies used are 143, 217 and 35…
Atmosphere mitigation in CMB observations using multi-frequency time-domain component separation
CNRS-UCB International Research Laboratory, Centre Pierre Binétruy（CNRS-UCB国际研究实验室，皮埃尔·比内特鲁中心）；Université Paris Cité（巴黎西岱大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Space Sciences Laboratory at University of California（加州大学空间科学实验室）
Current and planned observations of the cosmic microwave background (CMB) polarization anisotropies, with their ever increasing number of detectors, have reached a potential accuracy that requires a very demanding control of systematic effects. While some of these systematics can be reduced in the design of the instruments, others will have to be modeled and hopefully accounted for or corrected a posteriori. We propose QuickPol, a quick and accurate calculation of the full effective beam transfer function and of temperature to polarization leakage at the power spectra level, as induced by beam…
Mitigating half-wave plate systematics at the map-making level: calibration requirements for LiteBIRD
Università di Ferrara（费拉拉大学）；International School for Advanced Studies (SISSA)（国际高等研究院）；INFN Sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS, The University of Tokyo（东京大学宇宙物质理论研究中心卡弗里宇宙起源与演化前沿科学中心）；Suwa University of Science（诹访理科短期大学）；Okayama University（冈山大学）；Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎高等师范学院物理实验室）；Dipartimento di Fisica, Università di Roma（罗马大学物理系）
The B-Machine Telescope is the culmination of several years of development, construction, characterization and observation. The telescope is a departure from standard polarization chopping of correlation receivers to a half wave plate technique. Typical polarimeters use a correlation receiver to chop the polarization signal to overcome the $1/f$ noise inherent in HEMT amplifiers. B-Machine uses a room temperature half wave plate technology to chop between polarization states and measure the polarization signature of the CMB. The telescope has a demodulated $1/f$ knee of 5 mHz and an average se…
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. In this context, the northern hemisphere displays an anomalously low variance while the southern hemisphere appears unremarkable (consistent with expectations from the best-fitting theory, $Λ$CDM). While this is a well established result in temperature, the low signal-to-noise ratio in current polarization data prevents a similar compariso…
The Cosmic Microwave Background (CMB) Polarization plays an important role in current cosmological studies. CMB B-mode polarization is the most effective probe to primordial gravitational waves (PGWs) and a test of the inflation as well as other theories of the early universe such as bouncing and cyclic universe. So far, major ground-based CMB polarization experiments are located in the southern hemisphere.Recently, China has launched the Ali CMB Polarization Telescope (AliCPT) in Tibetan Plateau to measure CMB B mode polarization and detect the PGWs in northern hemisphere. AliCPT include two …
We present a method for the computation of the variance of cosmic microwave background (CMB) temperature maps on azimuthally symmetric patches using a fast convolution approach. As an example of the application of the method, we show results for the search for concentric rings with unusual variance in the 7-year WMAP data. We re-analyse claims concerning the unusual variance profile of rings centred at two locations on the sky that have recently drawn special attention in the context of the conformal cyclic cosmology scenario proposed by Penrose (2009). We extend this analysis to rings with la…
The most accessible method to measure polarization features of the CMB radiation is by means of a Stokes Polarimeter based on the rotation of an Half Wave Plate. The current observational cosmology is starting to be limited by the presence of systematic effects. The Stokes polarimeter with a rotating Half Wave Plate (HWP) has the advantage of mitigating a long list of potential systematics, by modulation of the linearly polarized component of the radiation, but the presence of the rotating HWP can by itself introduce new systematic effects, which must be under control, representing one of the …
Combining Systematic Effects in CMB Polarization Experiments through map-based simulations: application to LiteBIRD's HWP non-idealities and detectors non-linearity
Dipartimento di Fisica, Univ. La Sapienza（罗马大学物理系）；INFN Sezione di Roma（罗马国家核物理研究所）；Université Grenoble Alpes, CNRS, LPSC-IN2P3（格勒诺布尔阿尔卑斯大学）；High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS, The University of Tokyo（东京大学宇宙物质前沿研究中心）；International School for Advanced Studies (SISSA)（国际高等研究院）；INFN Sezione di Trieste（的里雅斯特国家核物理研究所）；Dipartimento di Fisica, Univ. of Milano-Bicocca（米兰比可卡大学物理系）
A continuously rotating half-wave plate (CRHWP) is a promising tool to improve the sensitivity to large angular scales in cosmic microwave background (CMB) polarization measurements. With a CRHWP, single detectors can measure three of the Stokes parameters, $I$, $Q$ and $U$, thereby avoiding the set of systematic errors that can be introduced by mismatches in the properties of orthogonal detector pairs. We focus on the implementation of CRHWPs in large aperture telescopes (i.e. the primary mirror is larger than the current maximum half-wave plate diameter of $\sim$0.5 m), where the CRHWP can b…
Cosmic polarization rotation, which may result from parity-violating new physics or the presence of primordial magnetic fields, converts $E$-mode polarization of the cosmic microwave background (CMB) into $B$-mode polarization. Anisotropic cosmic polarization rotation leads to statistical anisotropy in CMB polarization and can be reconstructed with quadratic estimator techniques similar to those designed for gravitational lensing of the CMB. At the sensitivity of upcoming CMB surveys, lensing-induced $B$-mode polarization will act as a limiting factor in the search for anisotropic cosmic polar…
We propose a machine learning approach to the blind detection of extragalactic point sources on maps of the temperature anisotropies of the cosmic microwave background. Using realistic simulations of the microwave sky as seen by Planck, we train a convolutional neural network (CNN) that solves source detection as an image segmentation problem. We divide the sky into regions of progressively increasing Galactic foreground intensity and independently train specialized CNNs for each region. This strategy leads to promising levels of completeness and reliability, with our CNN substantially outperf…
Exact map-space beam convolution via spin-mapmaking
Università degli Studi di Ferrara（费拉拉大学）；Università degli studi di Trento（特伦托大学）；Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara（意大利国家核物理研究所，费拉拉分部）；Institut d’Astrophysique Spatiale, CNRS, Univ. Paris-Sud, Université Paris-Saclay（空间天体物理研究所，法国国家科学研究中心，巴黎南大学，巴黎萨克雷大学）
Reaching the sufficient sensitivity to detect primordial B-modes requires modern CMB polarisation experiments to rely on new technologies, necessary for the deployment of arrays thousands of detectors with a broad frequency coverage and operating them for extended periods of time. This increased complexity of experimental design unavoidably introduces new instrumental and systematic effects, which may impact performance of the new instruments. In this work we extend the standard data analysis pipeline by including a (parametric) model of instrumental effects directly in the data model. We then…
Particles with masses much larger than the inflationary Hubble scale, $H_I$, can be pair-produced non-adiabatically during inflation. Due to their large masses, the produced particles modify the curvature perturbation around their locations. These localized perturbations eventually give rise to localized signatures on the Cosmic Microwave Background (CMB), in particular, pairwise hotspots (PHS). In this work, we show that Convolutional Neural Networks (CNN) provide a powerful tool for identifying PHS on the CMB. While for a given hotspot profile a traditional Matched Filter Analysis is known t…
In string theory inspired models of axion-like fields, sub-leading non-perturbative effects, if sufficiently large, can introduce steep cliffs and gentle plateaus onto the underlying scalar potential. During inflation, the motion of a spectator axion $σ$ on this potential becomes temporarily fast, leading to localized amplification of one helicity state of gauge fields. In this model, the tensor and scalar correlators sourced by the vector fields exhibit localized peak(s) in momentum space corresponding to the modes that exit the horizon while the roll of $σ$ is fast. Thanks to the gravitation…
