Primary Cosmic Microwave Background Research Articles

The Atacama Cosmology Telescope: Cosmology from Cross-correlations of unWISE Galaxies and ACT DR6 CMB Lensing

We present tomographic measurements of structure growth using cross-correlations of Atacama Cosmology Telescope (ACT) DR6 and Planck cosmic microwave background (CMB) lensing maps with the unWISE Blue and Green galaxy samples, which span the redshift ranges 0.2 ≲ z ≲ 1.1 and 0.3 ≲ z ≲ 1.8, respectively. We improve on prior unWISE cross-correlations not just by making use of the new, high-precision ACT DR6 lensing maps, but also by including additional spectroscopic data for redshift calibration and by analyzing our measurements with a more flexible theoretical model. We determine the amplitude of matter fluctuations at low redshifts (z ≃ 0.2–1.6), finding S8≡σ8(Ωm/0.3)0.5=0.813±0.021 using the ACT cross-correlation alone and S 8 = 0.810 ± 0.015 with a combination of Planck and ACT cross-correlations; these measurements are fully consistent with the predictions from primary CMB measurements assuming standard structure growth. The addition of baryon acoustic oscillation data breaks the degeneracy between σ 8 and Ω m , allowing us to measure σ 8 = 0.813 ± 0.020 from the cross-correlation of unWISE with ACT and σ 8 = 0.813 ± 0.015 from the combination of cross-correlations with ACT and Planck. These results also agree with the expectations from primary CMB extrapolations in ΛCDM cosmology; the consistency of σ 8 derived from our two redshift samples at z ∼ 0.6 and 1.1 provides a further check of our cosmological model. Our results suggest that structure formation on linear scales is well described by ΛCDM even down to low redshifts z ≲ 1.

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.

The impact of cross-covariances between the CMB and reconstructed lensing power

Weak gravitational lensing of the Cosmic Microwave Background (CMB) changes CMB statistics in a nontrivial way, allowing for reconstruction of the lensing potential and the use of these reconstructed maps in determining cosmological parameters that affect the formation of intervening large-scale structures. Although in principle there are correlations between the primary CMB and the reconstructed lensing potential due to the lensing procedure itself, in practice CMB analyses treat these as negligible when combining these band powers in likelihoods. In this paper we quantify explicitly the impact on parameter constraints due to these cross-covariances between the lensed CMB and reconstructed lensing power, and we compare to the effect of including all lensing-induced non-Gaussian covariances, which have previously shown to impact parameter constraints on the order of 10%. We perform our analysis for a range of experimental setups, scanning over instrumental noise levels of 0.5 to 10.0 μK-arcmin in temperature assuming fully polarized detectors, and using a fixed beam size of 1.4 arcmin. When the correlations between the lensed CMB and lensing power are neglected, we find that forecasted constraints shift by at most 3% of the error bar for a 6-parameter ΛCDM model, and for the noise levels considered in this paper. For some of the ΛCDM extensions considered here, however, these correlations have a nontrivial impact, in some cases more than 10% of the error bar, even for current experimental noise levels.

New Probe of Inflationary Gravitational Waves: Cross-Correlations of Lensed Primary CMB B-Modes with Large-Scale Structure.

We propose a new probe of inflationary gravitational waves (IGWs): the cross-correlation of the lensing of inflationary B-mode polarization with a large-scale structure (LSS) tracer, which can also be a cosmic microwave background (CMB) lensing map. This is equivalent to measuring a three-point function of two CMB B-modes and an LSS tracer. We forecast expected 1σ constraints on the tensor-to-scalar ratio r, albeit with a simplistic foreground treatment, and find constraints of σ_{r}≃7×10^{-3} from the correlation of CMB-S4-Deep B-mode lensing and LSST galaxies, σ_{r}≃5×10^{-3} from the correlation of CMB-S4-Deep B-mode lensing and CMB-S4-Deep CMB lensing, and σ_{r}≃10^{-2} from the correlation of LiteBIRD B-mode lensing and CMB-S4-Wide lensing. Because this probe is inherently non-Gaussian, simple Gaussian foregrounds will not produce any biases to the measurement of r. While a detailed investigation of non-Gaussian foreground contamination for different cross-correlations will be essential, this observable has the potential to be a useful probe of IGWs, which, due to different sensitivity to many potential sources of systematic errors, can be complementary to standard methods for constraining r.

Mass bias and cosmological constraints from Planck cluster clustering

Aims. We analysed the 3D clustering of the Planck sample of Sunyaev–Zeldovich (SZ) selected galaxy clusters, focusing on the redshift-space two-point correlation function (2PCF). We compared our measurements to theoretical predictions of the standard Λ cold dark matter (ΛCDM) cosmological model, deriving an estimate of the Planck mass bias, bSZ, and cosmological parameters. Methods. We measured the 2PCF of the sample in the cluster-centric radial range r ∈ [10, 150] h−1 Mpc, considering 920 galaxy clusters with redshift z ≤ 0.8. A Markov chain Monte Carlo analysis was performed to constrain bSZ, assuming priors on cosmological parameters from Planck cosmic microwave background (CMB) results. We also adopted priors on bSZ from external data sets to constrain the cosmological parameters Ωm and σ8. Results. We obtained (1−bSZ) = 0.62−0.11+0.14, which agrees with the value required to reconcile primary CMB and cluster count observations. By adopting priors on (1 − bSZ) from external data sets, we derived results on Ωm that fully agree and are competitive, in terms of uncertainties, with those derived from cluster counts. This confirms the importance of including clustering in cosmological studies in order to fully exploit the information from galaxy cluster statistics. On the other hand, we found that σ8 is not constrained.

Holographic energy density, dark energy sound speed, and tensions in cosmological parameters: H0 and S8

Interesting discrepancies in cosmological parameters are challenging the success of the ΛCDM model. Direct measurements of the Hubble constant H 0 using Cepheid variables and supernovae turn out to be higher than inferred from the Cosmic Microwave Background (CMB). Weak galaxy lensing surveys consistently report values of the strength of matter clustering σ 8 lower than values derived from the CMB in the context of ΛCDM. In this paper we address these discrepancies in cosmological parameters by considering Dark Energy (DE) as a fluid with evolving equation of state w de(z), constant sound speed squared ĉ s 2, and vanishing anisotropic stress σ. Our w de(z) is derived from the Holographic Principle and can consecutively exhibit radiation-like, matter-like, and DE-like behaviour, thus affecting the sound horizon and the comoving angular diameter distance, hence H 0. Here we show DE sound speed plays a part in the matter clustering behaviour through its effect on the evolution of the gravitational potential. We compute cosmological constraints using several data set combinations including primary CMB, CMB lensing, redshift-space-distortions, local distance-ladder, supernovae, and baryon acoustic oscillations. In our analysis we marginalise over ĉ s 2 and find ĉ s 2 = 1 is excluded at ≳ 3σ. For our baseline result including the whole data set we found H 0 and σ 8 in good agreement (within ≈ 2σ) with low redshift probes. Our constraint for the baryon energy density ω b is however in ≈ 3σ tension with BBN constraints. We conclude evolving DE also having non-standard clustering properties [e.g., ĉ s 2(z,k)] might be relevant for the solution of current discrepancies in cosmological parameters.

Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT andPlanck. II. Cross-correlation measurements and cosmological constraints

Cross-correlations of galaxy positions and galaxy shears with maps of gravitational lensing of the cosmic microwave background (CMB) are sensitive to the distribution of large-scale structure in the Universe. Such cross-correlations are also expected to be immune to some of the systematic effects that complicate correlation measurements internal to galaxy surveys. We present measurements and modeling of the cross-correlations between galaxy positions and galaxy lensing measured in the first three years of data from the Dark Energy Survey with CMB lensing maps derived from a combination of data from the 2500 deg2 SPT-SZ survey conducted with the South Pole Telescope and full-sky data from the Planck satellite. The CMB lensing maps used in this analysis have been constructed in a way that minimizes biases from the thermal Sunyaev Zel’dovich effect, making them well suited for cross-correlation studies. The total signal-to-noise of the cross-correlation measurements is 23.9 (25.7) when using a choice of angular scales optimized for a linear (nonlinear) galaxy bias model. We use the cross-correlation measurements to obtain constraints on cosmological parameters. For our fiducial galaxy sample, which consist of four bins of magnitude-selected galaxies, we find constraints of Ωm=0.272−0.052+0.032 and S8≡σ8Ωm/0.3=0.736−0.028+0.032 (Ωm=0.245−0.044+0.026 and S8=0.734−0.028+0.035) when assuming linear (nonlinear) galaxy bias in our modeling. Considering only the cross-correlation of galaxy shear with CMB lensing, we find Ωm=0.270−0.061+0.043 and S8=0.740−0.029+0.034. Our constraints on S8 are consistent with recent cosmic shear measurements, but lower than the values preferred by primary CMB measurements from Planck.12 MoreReceived 4 April 2022Accepted 30 September 2022DOI:https://doi.org/10.1103/PhysRevD.107.023530© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic microwave backgroundCosmological parametersLarge scale structure of the UniverseGravitation, Cosmology & Astrophysics

Testing for spectral index variations in polarized CMB foregrounds

ABSTRACT We present a Bayesian parametric component separation method for polarized microwave sky maps. We solve jointly for the primary cosmic microwave background (CMB) signal and the main Galactic polarized foreground components. For the latter, we consider electron-synchrotron radiation and thermal dust emission, modelled in frequency as a power law and a modified blackbody, respectively. We account for inter-pixel correlations in the noise covariance matrices of the input maps and introduce a spatial correlation length in the prior matrices for the spectral indices β. We apply our method to low-resolution polarized Planck 2018 Low and High Frequency Instrument (LFI/HFI) data, including the SRoll2 re-processing of HFI data. We find evidence for spatial variation of the synchrotron spectral index, and no evidence for depolarization of dust. Using the HFI SRoll2 maps, and applying wide priors on the spectral indices, we find a mean polarized synchrotron spectral index over the unmasked sky of $\bar{\beta }_{\rm sync}=-2.83\pm 0.62$. For polarized thermal dust emission, we obtain $\bar{\beta }_{\rm dust}=1.43\pm 0.24$. Using our recovered CMB maps and associated uncertainties, we constrain the optical depth to reionization, τ, using a cross-spectrum-based likelihood-approximation scheme (momento) to be τ = 0.0598 ± 0.0059. We confirm our findings using a pixel-based likelihood (pixLike). In both cases, we obtain a result that is consistent with that found by subtracting spatially uniform foreground templates. While the latter method is sufficient for current polarization data from Planck, next-generation space-borne CMB experiments will need more powerful schemes such as the one presented here.

E and B modes of the CMB y-type distortions: polarised kinetic Sunyaev-Zeldovich effect from the reionisation and post-reionisation eras

We study the E and B mode polarisation of the cosmic microwave background (CMB) originating from the transverse peculiar velocity of free electrons, at second order in perturbation theory, during the reionisation and post-reionisation eras. Interestingly, the spectrum of this polarised kinetic Sunyaev-Zeldovich (SZ) effect can be decomposed into a blackbody part and a y-type distortion. The y-distortion part is distinguishable from the primary E and B modes and also the lensing B modes. Furthermore, it is also differentiable from the other y-type signals, such as the thermal SZ effect, which are unpolarised. We show that this signal is sensitive to the reionisation history, in particular to how fast reionisation happens. The E and B modes of y-type distortion provide a way to beat the cosmic variance of primary CMB anisotropies and are an independent probe of the cosmological parameters. The blackbody component of the pkSZ effect would be an important foreground for the primordial tensor modes for tensor to scalar ratio r ≲ 3 × 10-5.

Spectral distortion anisotropy from inflation for primordial black holes

Single-field inflationary models that seek to greatly enhance small-scale power in order to form primordial black holes predict both a squeezed bispectrum that is enhanced by this small-scale power and a potentially detectable enhancement of cosmic microwave background (CMB) spectral distortions. Despite this combination, spectral distortion anisotropy on CMB scales remains small since the squeezed bispectrum represents an unobservable modulation of the scale rather than local amplitude for the short-wavelength acoustic power that dissipates and forms the $\ensuremath{\mu}$ spectral distortion. The leading-order amplitude effect comes from the local modulation of acoustic dissipation at the beginning of the $\ensuremath{\mu}$ epoch at the end of thermalization by a long-wavelength mode that is correlated with CMB anisotropy itself. Compensating factors from the suppression by the square of the ratio the comoving horizon at thermalization to the smallest detectable primary CMB scales ($\ensuremath{\sim}0.0005$) and maximal allowed enhancement of $\ensuremath{\mu}$ ($\ensuremath{\sim}5000$) leaves a signal in the $\ensuremath{\mu}T$ cross spectrum that is still well beyond the capabilities of PIXIE or LiteBIRD space missions due to sensitivity and resolution while remaining much larger than in single-field slow-roll inflation and potentially observable.

Joint constraints on cosmology and the impact of baryon feedback: Combining KiDS-1000 lensing with the thermal Sunyaev–Zeldovich effect from Planck and ACT

We conduct a pseudo-Cℓ analysis of the tomographic cross-correlation between 1000 deg2 of weak-lensing data from the Kilo-Degree Survey (KiDS-1000) and the thermal Sunyaev–Zeldovich (tSZ) effect measured by Planck and the Atacama Cosmology Telescope (ACT). Using HMX, a halo-model-based approach that consistently models the gas, star, and dark matter components, we are able to derive constraints on both cosmology and baryon feedback for the first time from these data, marginalising over redshift uncertainties, intrinsic alignment of galaxies, and contamination by the cosmic infrared background (CIB). We find our results to be insensitive to the CIB, while intrinsic alignment provides a small but significant contribution to the lensing–tSZ cross-correlation. The cosmological constraints are consistent with those of other low-redshift probes and prefer strong baryon feedback. The inferred amplitude of the lensing–tSZ cross-correlation signal, which scales as σ8(Ωm/0.3)0.2, is low by ∼2 σ compared to the primary cosmic microwave background constraints by Planck. The lensing–tSZ measurements are then combined with pseudo-Cℓ measurements of KiDS-1000 cosmic shear into a novel joint analysis, accounting for the full cross-covariance between the probes, providing tight cosmological constraints by breaking parameter degeneracies inherent to both probes. The joint analysis gives an improvement of 40% on the constraint of S8 = σ8Ωm/0.3 over cosmic shear alone, while providing constraints on baryon feedback consistent with hydrodynamical simulations, demonstrating the potential of such joint analyses with baryonic tracers such as the tSZ effect. We discuss remaining modelling challenges that need to be addressed if these baryonic probes are to be included in future precision-cosmology analyses.

Ultralight axions and the kinetic Sunyaev-Zel’dovich effect

Measurements of secondary cosmic microwave background (CMB) anisotropies, such as the Sunyaev-Zel'dovich (SZ) effect, will enable new tests of neutrino and dark sector properties. The kinetic SZ (kSZ) effect is produced by cosmological flows, probing structure growth. Ultra-light axions (ULAs) are a well-motivated dark-matter candidate. Here the impact of ULA dark matter (with mass $10^{-27}~{\rm eV}$ to $10^{-23}~{\rm eV}$) on kSZ observables is determined, applying new analytic expressions for pairwise cluster velocities and Ostriker-Vishniac signatures in structure-suppressing models. For the future CMB-S4 and ongoing DESI galaxy surveys, the kSZ effect (along with primary anisotropies) will probe ULA fractions $\eta_a = \Omega_{\rm{axion}}/\Omega_{\rm DM}$ as low as $\sim 5\%$ if $m_{a}\simeq 10^{-27}~{\rm eV}$ (at 95\% C.L.), with sensitivity extending up to $m_{a}\simeq 10^{-25}~{\rm eV}$. If reionization and the primary CMB can be adequately modeled, Ostriker-Vishniac measurements could probe values $\eta_{a}\simeq 10^{-3}$ if $10^{-27}~{\rm eV}\lesssim m_{a}\lesssim 10^{-24}~{\rm eV}$, or $\eta_{a}\simeq 1$ if $m_{a}\simeq 10^{-22}~{\rm eV}$, within the fuzzy dark matter window.

Assessing the Importance of Noise from Thermal Sunyaev–Zel′dovich Signals for CMB Cluster Surveys and Cluster Cosmology

Abstract We explore the significance of noise from thermal Sunyaev–Zel’dovich (tSZ) signals for cluster detection using cosmic microwave background (CMB) surveys. The noise arises both from neighboring objects and also from haloes below the detection limit. A wide range of surveys are considered: SPT-SZ, SPTpol, and SPT-3G from the South Pole Telescope; SO-Baseline and SO-Goal configurations for Simons Observatory; CMB-S4's wide-area (S4-Wide) and deep (S4-Ultra deep) surveys; and the futuristic CMB-HD experiment. We find that the noise from tSZ signals has a significant impact on CMB-HD and to some extent on S4-Ultra deep. For other experiments, the effect is negligible as the noise in the tSZ map is dominated by residual foregrounds or experimental noise. In the limit when the noise from tSZ signals is important, we find that removing the detected clusters and rerunning the cluster finder allows us to find a new set of less massive and distant clusters. Since the detected clusters are the dominant source of the tSZ power, removing them reduces the power at ℓ = 3000 by ×5 for CMB-HD; ×3.1 of S4-Ultra deep; ×2.4 for S4-Wide and SPT-3G; ×1.5 for SO-Goal and SPTpol; ×1.35 for SO-Baseline; and ×1.08 for SPT-SZ. We forecast the expected number of clusters and also derive parameter constraints by combining cluster counts with primary CMB and tSZ power spectra finding that the future surveys can reduce the error on the dark energy equation of state parameter to sub-percent levels and can also enable ≥3σ detection of the sum of neutrino masses.

Catalog of X-ray-selected extended galaxy clusters from the ROSAT All-Sky Survey (RXGCC)

Context. There is a known tension between cosmological parameter constraints obtained from the primary cosmic microwave background and those drawn from galaxy cluster samples. One possible explanation for this discrepancy may be that the incomplete character of detected clusters is higher than estimated and, as a result, certain types of groups or galaxy clusters have been overlooked in the past. Aims. We aim to search for galaxy groups and clusters with particularly extended surface brightness distributions by creating a new X-ray-selected catalog of extended galaxy clusters from the ROSAT All-Sky Survey (RASS), based on a dedicated source detection and characterization algorithm that is optimized for extended sources. Methods. Our state-of-the-art algorithm includes multi-resolution filtering, source detection, and characterization. On the basis of extensive simulations, we investigated the detection efficiency and sample purity. We used previous cluster catalogs in X-ray and other bands, as well as spectroscopic and photometric redshifts of galaxies to identify clusters. Results. We report a catalog of galaxy clusters at high galactic latitude based on the ROSAT All-sky Survey, known as the RASS-based extended X-ray Galaxy Cluster Catalog, which includes 944 groups and clusters. Of this number, 641 clusters have been previously identified based on intra-cluster medium (ICM) emission (Bronze), 154 known optical and infrared clusters are detected as X-ray clusters for the first time (Silver) and 149 are identified as clusters for the first time (Gold). Based on 200 simulations, the contamination ratio of the detections that were identified as clusters by ICM emission and the detections that were identified as optical and infrared clusters in previous work is 0.008 and 0.100, respectively. Compared with the Bronze sample, the Gold+Silver sample is less luminous, less massive, and exhibits a flatter surface brightness profile. Specifically, the median flux in [0.1−2.4] keV band for Gold+Silver and Bronze sample is 2.496 × 10−12 erg s−1 cm−2 and 4.955 × 10−12 erg s−1 cm−2, respectively. The median value of β (the slope of cluster surface brightness profile) is 0.76 and 0.83 for the Gold+Silver and Bronze sample, respectively.

Primordial tensor bispectra in μ-CMB cross-correlations

Cross-correlations between Cosmic Microwave Background (CMB) temperature and polarization anisotropies and μ-spectral distortions have been considered to measure (squeezed) primordial scalar bispectra in a range of scales inaccessible to primary CMB bispectra. In this work we address whether it is possible to constrain tensor non-Gaussianities with these cross-correlations. We find that only primordial tensor bispectra with statistical anisotropies leave distinct signatures, while isotropic tensor bispectra leave either vanishing or highly suppressed signatures. We discuss how the angular dependence of squeezed bispectra in terms of the short and long momenta determine the non-zero cross-correlations. We also discuss how these non-vanishing configurations are affected by the way in which primordial bispectra transform under parity. By employing the so-called BipoSH formalism to capture the observational effects of statistical anisotropies, we make Fisher-forecasts to assess the detection prospects from μ T, μ E and μ B cross-correlations. Observing statistical anisotropies in squeezed ⟨γγγ⟩ and ⟨γγζ⟩ bispectra is going to be challenging as the imprint of tensor perturbations on μ-distortions is subdominant to scalar perturbations, therefore requiring a large, independent amplification of the effect of tensor perturbations in the μ-epoch. In absence of such a mechanism, statistical anisotropies in squeezed ⟨ζζγ⟩ bispectrum are the most relevant sources of μ T, μ E and μ B cross-correlations. In particular, we point out that in anisotropic inflationary models where ⟨ζζζ⟩ leaves potentially observable signatures in μ T and μ E, the detection prospects of ⟨ζζγ⟩ from μ B are enhanced.

Constraining Cluster Virialization Mechanism and Cosmology Using Thermal-SZ-selected Clusters from Future CMB Surveys

Abstract We forecast the number of galaxy clusters that can be detected via the thermal Sunyaev–Zel’dovich (tSZ) signals by future cosmic microwave background (CMB) experiments, primarily the wide area survey of the CMB-S4 experiment but also CMB-S4's smaller de-lensing survey and the proposed CMB-HD experiment. We predict that CMB-S4 will detect 75,000 clusters with its wide survey of f sky = 50% and 14,000 clusters with its deep survey of f sky = 3%. Of these, approximately 1350 clusters will be at z ≥ 2, a regime that is difficult to probe by optical or X-ray surveys. We assume CMB-HD will survey the same sky as the S4-Wide, and find that CMB-HD will detect three times more overall and an order of magnitude more z ≥ 2 clusters than CMB-S4. These results include galactic and extragalactic foregrounds along with atmospheric and instrumental noise. Using CMB-cluster lensing to calibrate the cluster tSZ–mass scaling relation, we combine cluster counts with primary CMB to obtain cosmological constraints for a two-parameter extension of the standard model (ΛCDM + ∑m ν + w 0). In addition to constraining σ(w 0) to ≲1%, we find that both surveys can enable a ∼2.5–4.5σ detection of ∑m ν , substantially strengthening CMB-only constraints. We also study the evolution of the intracluster medium by modeling the cluster virialization v(z) and find tight constraints from CMB-S4, with further factors of three to four improvement for CMB-HD.

Baryonic feedback biases on fundamental physics from lensed CMB power spectra

Upcoming measurements of the small-scale primary cosmic microwave background (CMB) temperature and polarization power spectra ($TT$/$TE$/$EE$) are anticipated to yield transformative constraints on new physics, including the effective number of relativistic species in the early universe ($N_{\rm eff}$). However, at multipoles $\ell \gtrsim 3000$, the primary CMB power spectra receive significant contributions from gravitational lensing. While these modes still carry primordial information, their theoretical modeling requires knowledge of the CMB lensing convergence power spectrum, $C_L^{\kappa\kappa}$, including on small scales where it is affected by nonlinear gravitational evolution and baryonic feedback processes. Thus, the high-$\ell$ primary CMB is sensitive to these late-time, nonlinear effects. Here, we show that inaccuracies in the modeling of $C_L^{\kappa\kappa}$ can yield surprisingly large biases on cosmological parameters inferred from the primary CMB power spectra measured by the upcoming Simons Observatory and CMB-S4 experiments. For CMB-S4, the biases can be as large as $1.6\sigma$ on the Hubble constant $H_0$ in a fit to $\Lambda$CDM and $1.2\sigma$ on $N_{\rm eff}$ in a fit to $\Lambda$CDM+$N_{\rm eff}$. We show that these biases can be mitigated by explicitly discarding all $TT$ data at $\ell>3000$ or by marginalizing over parameters describing baryonic feedback processes, both at the cost of slightly larger error bars. We also discuss an alternative, data-driven mitigation strategy based on delensing the CMB $T$ and $E$-mode maps. Finally, we show that analyses of upcoming data will require Einstein-Boltzmann codes to be run with much higher numerical precision settings than is currently standard, so as to avoid similar -- or larger -- parameter biases due to inaccurate theoretical predictions.

Reconstructing patchy reionization with deep learning

The precision anticipated from next-generation cosmic microwave background (CMB) surveys will create opportunities for characteristically new insights into cosmology. Secondary anisotropies of the CMB will have an increased importance in forthcoming surveys, due both to the cosmological information they encode and the role they play in obscuring our view of the primary fluctuations. Quadratic estimators have become the standard tools for reconstructing the fields that distort the primary CMB and produce secondary anisotropies. While successful for lensing reconstruction with current data, quadratic estimators will be suboptimal for the reconstruction of lensing and other effects at the expected sensitivity of the upcoming CMB surveys. In this paper we describe a convolutional neural network, ResUNet-CMB, that is capable of the simultaneous reconstruction of two sources of secondary CMB anisotropies, gravitational lensing and patchy reionization. We show that the ResUNet-CMB network significantly outperforms the quadratic estimator at low noise levels and is not subject to the lensing-induced bias on the patchy reionization reconstruction that would be present with a straightforward application of the quadratic estimator.

An Improved Measurement of the Secondary Cosmic Microwave Background Anisotropies from the SPT-SZ + SPTpol Surveys

Abstract We report new measurements of millimeter-wave power spectra in the angular multipole range 2000 ≤ ℓ ≤ 11,000 (angular scales ). By adding 95 and 150 GHz data from the low-noise 500 deg2 SPTpol survey to the SPT-SZ three-frequency 2540 deg2 survey, we substantially reduce the uncertainties in these bands. These power spectra include contributions from the primary cosmic microwave background, cosmic infrared background, radio galaxies, and thermal and kinematic Sunyaev–Zel’dovich (SZ) effects. The data favor a thermal SZ (tSZ) power at 143 GHz of and a kinematic SZ (kSZ) power of . This is the first measurement of kSZ power at ≥3σ. However, different assumptions about the CIB or SZ models can reduce the significance down to 2.4σ in the worst case. We study the implications of the measured kSZ power for the epoch of reionization under the Calabrese et al. model for the kSZ power spectrum and find the duration of reionization to be ( at 95% confidence), when combined with our previously published tSZ bispectrum measurement. The upper limit tightens to if the assumed homogeneous kSZ power is increased by 25% (∼0.5 μK2) and relaxes to if the homogeneous kSZ power is decreased by the same amount.

Cosmology with Rayleigh scattering of the cosmic microwave background

The cosmic microwave background (CMB) has been a treasure trove for cosmology. Over the next decade, current and planned CMB experiments are expected to exhaust nearly all primary CMB information. To further constrain cosmological models, there is a great benefit to measuring signals beyond the primary modes. Rayleigh scattering of the CMB is one source of additional cosmological information. It is caused by the additional scattering of CMB photons by neutral species formed during recombination and exhibits a strong and unique frequency scaling (∝ ν4). We will show that with sufficient sensitivity across frequency channels, the Rayleigh scattering signal should not only be detectable but can significantly improve constraining power for cosmological parameters, with limited or no additional modifications to planned experiments. We will provide heuristic explanations for why certain cosmological parameters benefit from measurement of the Rayleigh scattering signal, and confirm these intuitions using the Fisher formalism. In particular, observation of Rayleigh scattering allows significant improvements on measurements of Neff and ∑ mν.