CMB-S4: Iterative Internal Delensing and r Constraints

Belkner, Sebastian; Carron, Julien; Legrand, Louis; Umiltà, Caterina; Pryke, Clem; Bischoff, Colin; ,

doi:10.3847/1538-4357/ad2351

Cited by 7 publications

(1 citation statement)

References 91 publications

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“…than 5-σ in the presence of primordial gravitational waves, or to rule them out at an upper limit of r < 0.001 at 95% confidence [82][83][84][85].…”

Section: Single-field Inflation Tensor Consistency Conditionmentioning

confidence: 99%

Improving constraints on inflation with CMB delensing

Trendafilova,

Hotinli,

Meyers

2024

J. Cosmol. Astropart. Phys.

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The delensing of cosmic microwave background (CMB) maps will be increasingly valuable for extracting as much information as possible from future CMB surveys. Delensing provides many general benefits, including sharpening of the acoustic peaks, more accurate recovery of the damping tail, and reduction of lensing-induced B-mode power. In this paper we present several applications of delensing focused on testing theories of early-universe inflation with observations of the CMB. We find that delensing the CMB results in improved parameter constraints for reconstructing the spectrum of primordial curvature fluctuations, probing oscillatory features in the primordial curvature spectrum, measuring the spatial curvature of the universe, and constraining several different models of isocurvature perturbations. In some cases we find that delensing can recover almost all of the constraining power contained in unlensed spectra, and it will be a particularly valuable analysis technique to achieve further improvements in constraints for model parameters whose measurements are not expected to improve significantly when utilizing only lensed CMB maps from next-generation CMB surveys. We also quantify the prospects of testing the single-field inflation tensor consistency condition using delensed CMB data; we find it to be out of reach of current and proposed experimental technology and advocate for alternative detection methods.

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“…than 5-σ in the presence of primordial gravitational waves, or to rule them out at an upper limit of r < 0.001 at 95% confidence [82][83][84][85].…”

Section: Single-field Inflation Tensor Consistency Conditionmentioning

confidence: 99%

Improving constraints on inflation with CMB delensing

Trendafilova,

Hotinli,

Meyers

2024

J. Cosmol. Astropart. Phys.

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Spherical bispectrum expansion and quadratic estimators

Carron,

Lewis

2024

J. Cosmol. Astropart. Phys.

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We describe a general expansion of spherical (full-sky) bispectra into a set of orthogonal modes. For squeezed shapes, the basis separates physically-distinct signals and is dominated by the lowest moments. In terms of reduced bispectra, we identify a set of discrete polynomials that are pairwise orthogonal with respect to the relevant Wigner 3j symbol, and reduce to Chebyshev polynomials in the flat-sky (high-momentum) limit for both parity-even and parity-odd cases. For squeezed shapes, the flat-sky limit is equivalent to previous moment expansions used for CMB bispectra and quadratic estimators, but in general reduces to a distinct expansion in the angular dependence of triangles at fixed total side length (momentum). We use the full-sky expansion to construct a tower of orthogonal CMB lensing quadratic estimators and construct estimators that are immune to foregrounds like point sources or noise inhomogeneities. In parity-even combinations (such as the lensing gradient mode from TT, or the lensing curl mode from EB) the leading two modes can be identified with information from the magnification and shear respectively, whereas the parity-odd combinations are shear-only. Although not directly separable, we show that these estimators can nonetheless be evaluated numerically sufficiently easily.

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AB C MB : deep delensing assisted likelihood-free inference from CMB polarization maps

Yi,

Fan,

Hamann

et al. 2024

Mach. Learn.: Sci. Technol.

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The existence of a cosmic background of primordial gravitational waves (PGWB) is a robust prediction of inflationary cosmology, but it has so far evaded discovery. The most promising avenue of its detection is via measurements of Cosmic Microwave Background (CMB) $B$-polarization. However, this is not straightforward due to (a) the fact that CMB maps are distorted by gravitational lensing and (b) the high-dimensional nature of CMB data, which renders likelihood-based analysis methods computationally extremely expensive. In this paper, we introduce an efficient likelihood-free, end-to-end inference method to directly infer the posterior distribution of the tensor-to-scalar ratio $r$ from lensed maps of the Stokes $Q$ and $U$ polarization parameters. Our method employs a generative model to delense the maps and utilizes the Approximate Bayesian Computation (ABC) algorithm to sample $r$. We demonstrate that our method yields unbiased estimates of $r$ with well-calibrated uncertainty quantification.

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CMB-S4: Iterative Internal Delensing and r Constraints

Cited by 7 publications

References 91 publications

Improving constraints on inflation with CMB delensing

Improving constraints on inflation with CMB delensing

Spherical bispectrum expansion and quadratic estimators

AB C MB : deep delensing assisted likelihood-free inference from CMB polarization maps

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