Session B03: Large Scale Structure and CMB

H0 from cosmological energy-density measurements: Big Bang Nucleosynthesis, the BAO amplitude, and the Alcock-Paczynski effect

The Hubble tension has reached >5-σ significance, demanding a change to the ΛCDM model barring unknown systematics in local or CMB measurements. H₀ from the CMB can be increased by decreasing the sound horizon at recombination, for instance by adding extra early dark energy (EDE) at z~1000. Hence, sound horizon free H₀ measurements provide a model-independent test of the Hubble tension. We measure H₀ without the sound horizon by combining Ω_m from the Alcock-Paczynski effect, Ω_bh² from Big Bang Nucleosynthesis calibrated via the primordial helium and deuterium abundance, and Ω_b/Ω_m from the amplitude of the baryon acoustic feature. The first two measurements are well-established in previous work; we validate BAO amplitude measurements using N-body mocks and apply it to BOSS data. We find that two separate approaches are consistent: adding BAO amplitude as an extra parameter to “template-fit” pre- and post-reconstruction BAO models with a damped linear power spectrum; and adding BAO amplitude to the full-shape perturbation theory code CLASS-PT. We explicitly verify that this method is sound-horizon independent by recovering the correct baryon fraction and H₀ using an EDE model as mock data. We measure the baryon fraction to ~15% across all BOSS redshift bins, leading to ~7% measurements of H0 (σ_H0 ~ 5.5) when combining with BBN and the Alcock-Paczynski parameter from voids. DESI Y5 will improve the precision of this measurement by a factor of 3, allowing 4-σ differentiation of local and CMB values of H₀.   

MUSE: A new algorithm for accelerated Bayesian inference with applications to CMB and large-scale-structure correlations

Bayesian inference offers a powerful framework for extracting cosmological information from observations which is automatically statistically optimal and straightforward to construct. Its main challenge is high computational cost, particularly for cosmological applications, which feature large numbers of parameter dimensions and non-Gaussian Bayesian posterior distributions. Here, I present a new algorithm, the Marginal Unbiased Score Expansion (MUSE) method, which accelerates inference over state-of-the-art Hamiltonian Monte Carlo methods by as much as factors of 500.

I will describe the algorithm and its associated software packages, with an aim to give listeners the needed understanding to apply to their own Bayesian problems in cosmology. I will then present some example applications. First, in the machine learning domain, it can be used to speed up Bayesian neural network analyses. Second, it has, for the first time, made possible a Bayesian analysis of high-resolution lensed CMB data. I will introduce its application to South Pole Telescope data, where it is being used to reduce lensing reconstruction noise by factor of ~2 compared to standard quadratic estimator approaches and will soon provide our tightest ground-based constraints on cosmological parameters such as the Hubble constant (an in-depth discussion of this is given in a separate talk). I will also describe our plans to extend this analysis to incorporate BICEP/Keck data and eventually CMB-S4 data, where it will provide the necessary delensing allowing CMB-S4 to achieve its stated goals for primordial gravitational wave detection. Finally, I will describe preliminary work using MUSE to perform the first Bayesian and optimal cross-correlation analysis between CMB data and large-scale structure.   

Testing ΛCDM with forthcoming SPT-3G measurements of CMB and CMB lensing power spectra

The South Pole Telescope (SPT) is a 10m telescope specifically engineered for low-noise and high-angular-resolution measurements of the millimeter-wave sky. In this talk, we describe the surveys currently being conducted with the SPT and its third-generation camera (SPT-3G) and how they can be used to test the ΛCDM model in several ways. Based on achieved performance, we forecast expected uncertainties on temperature and E-mode polarization power spectra, their cross power spectrum, and the gravitational lensing power spectrum. We also propagate the power spectrum uncertainties forward to constraints on cosmological parameters. We find that, assuming ΛCDM, data from SPT-3G alone enable about two orders of magnitude of reduction in the allowed six-dimensional parameter volume relative to the volume allowed by Planck data. Given that these constraints come from signals largely different from those measured by Planck (more weight on smaller scales, polarization, and gravitational lensing), a consistency test with Planck parameter estimates will be a significant test of the ΛCDM model. We will also discuss some proposed alternatives to the ΛCDM model that reduce the S8 or H0 tensions and discuss the potential of the SPT-3G surveys to test these models.   

Optimal Cosmic Microwave Background Gravitational Lensing Reconstruction, Delensing, and Parameter Estimation with SPT-3G Polarization Data

I will present simultaneous Bayesian estimates of gravitational-lensing potential bandpowers and unlensed cosmic microwave background (CMB) bandpowers derived from South Pole Telescope (SPT) observations in 2019 and 2020, as well as cosmological parameter estimates enabled by these spectra. These observations produce the deepest-ever high-angular-resolution CMB polarization maps at 90, 150, and 220 GHz. At these depths the standard Quadratic Estimation (QE) lensing reconstruction method is suboptimal. We use the Marginal Unbiased Score Expansion (MUSE) method to perform optimal map-level Bayesian inference of lensing potential bandpowers and unlensed CMB EE bandpowers, effectively using all N-point statistics of the CMB polarization maps. With CMB polarization maps from SPT-3G 2019/20 observations, the MUSE lensing reconstruction noise is ~2 times smaller than the QE estimation. Unlensed (or de-lensed) power spectra have lower sample variance and sharper features, in principle allowing for tighter constraints on cosmological parameters.   

Cosmological parameters from CMB temperature and E-mode polarization anisotropies with 2019 and 2020 data from the South Pole Telescope

SPT-3G, the third-generation camera on the South Pole Telescope, is being used to observe the cosmic microwave background (CMB) anisotropies to unprecedented depth at arcminute resolution. The temperature and E-mode polarization anisotropies of the CMB provide a wealth of information on the composition and evolution of the universe. Upcoming constraints on cosmological parameters from power spectrum analyses based on data collected in 2019/2020 will be comparable to Planck’s, while remaining mostly independent from the satellite experiment, thus allowing to test the consistency of the two data sets and potentially discover evidence of new physics. In this talk, I will describe the analysis pipeline, showcase our measurement and outline the steps towards cosmological parameters.<!-- notionvc: bcef5ff6-7dff-4a22-bd4f-9c7a6892bdc1 -->   

Foreground-Immune Curved-Sky Lensing Reconstruction with SPT-3G 2019+2020 Data

Weak gravitational lensing of the cosmic microwave background (CMB) is a powerful probe of fundamental physics, and offers insight into the structure and evolution of the universe. SPT-3G is an ongoing high angular resolution and low noise CMB experiment providing ideal temperature and polarization maps for the purpose of reconstructing the lensing potential. For the upcoming SPT-3G lensing analysis using data collected during the 2019 and 2020 observing seasons, we use the global minimum variance (GMV) estimator in the curved sky formalism, which is shown to have up to a 10% improvement in noise compared to the standard quadratic estimator. With this estimator, we expect the statistical uncertainty on the lensing amplitude to be about 2% for this analysis. In this talk, we present an extension to the GMV estimator with various foreground mitigation techniques, which makes our measurements more robust against contamination from astrophysical sources. We also discuss the cosmological parameter results from the 2019-2020 SPT-3G lensing measurements.   

The Simons Observatory: Status of the Small-Aperture Telescope Program

The Simons Observatory (SO) is a cosmic microwave background (CMB) experiment consisting of a set of four telescopes sited at 5200 m elevation in the Atacama Desert of Chile. To pursue the key science goal of constraining the amplitude of primordial gravitational waves in the early universe, SO features three small-aperture telescopes (SATs) observing in atmospheric transmission windows centered at 90, 150, 220, and 280 GHz. Each instrument features a cryogenically-cooled rotating half-wave plate used as a polarization modulator, a refractive optical design featuring silicon lenses with metamaterial anti-reflection coatings, and a focal plane of seven close-packed arrays of horn-coupled transition-edge sensor bolometers. Each of the more than 3,000 pixels in the focal plane is sensitive to both linear polarizations in two frequency bands, with four bolometers per pixel for a total of 12,000 detectors. These devices are read out using GHz resonators in a microwave-multiplexing scheme. All three instruments are in the field and moving toward initial science observations of the CMB across roughly 10% of the sky. In this presentation, I will report on the as-deployed design and early performance results of the SATs, as well as the observing strategy planned for them and the ambitious science goals which they will enable when fully operational.   

LiteBIRD: Next generation all-sky surveys of cosmic microwave background polarization

LiteBIRD is a next generation space mission designed to explore early universe and fundamental physics. JAXA selected LiteBIRD as a future large-class (L-class) mission in May 2019. LiteBIRD's goal is to conduct all sky survey of polarization of the cosmic microwave background (CMB) with unparalleled precision.

The principal scientific objective of LiteBIRD is to conduct a study of the signal imprinted into the CMB from cosmic primordial inflation. LiteBIRD will search for the B-mode polarization signal from primordial inflation with the goal of reaching a tensor-to-scalar ratio sensitivity of σr ~ 0.001.. With such sensitivity LiteBIRD will be able to make a groundbreaking discovery or exclude well-motivated inflationary models. The measurements obtained by LiteBIRD also offer insights into the quantum properties of gravity and other fields of particle physics and cosmology.

The LiteBIRD mission will embark on an all-sky survey spanning three years from the Sun-Earth Lagrangian point L2. This mission will encompass observations across 15 distinct frequency bands, ranging from 34 to 448 GHz, with three telescopes. Ultra sensitive instrument that utilizes superconducting Transition Edge Sensors detector arrays will achieve a total sensitivity of 2.16 micro K-arcmin,with an angular resolution of 0.5 degrees at 100 GHz.

In this talk, we will go over scientific objectives, mission design and status, and the anticipated scientific outcomes of the LiteBIRD mission