Session K15: Cosmic Microwave Background

Science Prospects for CMB-S4: Project Overview and Instrument Design

CMB-S4 is a ground-based cosmic microwave background (CMB) experiment, currently funded in design phase to enable transformative measurements with implications spanning cosmology, astrophysics, and fundamental physics.  Key science goals include searching for evidence of primordial gravitational waves, probing the dark Universe and neutrino sector, mapping the matter distribution of the cosmos, and exploring the transient millimeter-wave sky.  With dedicated telescopes performing deep and wide surveys from the South Pole and Atacama Desert, the maps produced by CMB-S4 from the primordial Universe to large scale structure will offer a valuable resource to the broader community.  This talk will highlight the scientific potential of CMB-S4 alongside the instrumentation that will enable these challenging measurements.   

Cosmology and Astrophysics with the Atacama Cosmology Telescope

I will present the latest maps of the millimeter-wave sky as seen by the Atacama Cosmology Telescope (ACT), and describe how they are advancing our knowledge of cosmology via significantly improved measurements of the cosmic microwave background (CMB).  I will discuss constraints on the cosmological model derived from the ACT CMB power spectra, including the standard LCDM model and several extensions involving new physics.  I will also present our latest sample of thousands of galaxy clusters obtained from these maps, as well as our latest maps of the distribution of dark matter inferred from gravitational lensing of the CMB, and maps of the gas distribution around groups and clusters.  I will briefly highlight novel astrophysical applications of these maps, including searches for transient signals and thermal emission from a potential Planet 9.  I will conclude with a look ahead to forthcoming CMB data from ACT, which will provide a powerful test of the cosmological model in a currently-uncharted regime.   

Overview and Status of the Simons Observatory

The Simons Observatory (SO) is a next generation Cosmic Microwave Background (CMB) experiment that is under construction in the Chilean Atacama Desert. SO’s scientific objectives encompass the characterization of the primordial perturbations, the measurement of the number of relativistic species and the sum of the mass of neutrinos, improving our understanding of galaxy evolution, and constraining the duration of reionization. SO will accomplish these goals using a single 6-m large-aperture telescope (LAT) to focus on the smaller angular scales and three 0.5-m small-aperture telescopes (SATs) to focus on the larger angular scales. These telescopes will contain nearly 60,000 transition edge sensor bolometers spread across size frequency bands from 30-280 GHz. I will review the scientific objectives and forecasts as well as the survey and instrument designs and status.   

BICEP Array Upgrades, Primordial Gravitational Wave Constraint Forecasts, and Low-Frequency Receiver Performance

The recently deployed BA1 receiver will allow BICEP Array (BA) to set competitive limits on galactic synchrotron as a contaminant to cosmic microwave background (CMB) polarization observations, and the full BA will continue the BICEP/Keck program's legacy of leading constraints on primordial gravitational waves (PGW). BA is an array of CMB polarimeters at the South Pole, seeking to constrain the amplitude of PGW via "B-mode" polarization. B-modes are now the path to improving constraints on the tensor-to-scalar ratio, r, given the cosmic-variance saturation of temperature-based probes. The first 30+40 GHz "BA1" receiver began observations in 2020, and the BA2/3/4 receivers at 150/95/220+270 GHz, respectively, are under construction and set to deploy imminently. These will allow the full BA to constrain r < 0.003 by 2027. BA will work with SPT-3G to account for the B-mode signal from gravitationally lensed E-modes, which has recently become BICEP/Keck's most limiting factor in constraining r. In this presentation, I will discuss the performance of BA1 in its first two observing seasons, ongoing efforts to upgrade BA to its full configuration, and forecasts for constraints on primordial gravitational waves.   

Probing inflationary cosmology with BICEP-Keck small aperture telescopes

This talk will overview the trajectory of small aperture telescopes, deployed by the BICEP-Keck collaboration, to understand the process of inflation. We will review the state-of-the art and the future CMB-Stage4 project in this regard. Cosmic Microwave Background (CMB) measurements indicate a period of inflation occurred immediately following the Big-Bang, during which the universe expanded some 60 e-folds and primordial gravitational waves (PGWs) were generated. PGWs are tensor perturbations and leave their signature on the CMB as polarized anisotropies, commonly called B-modes. Detection of B-modes will directly probe inflation and will reveal physics at 10^16 GeV energy-scales, a trillion times larger than any terrestrial collider experiment. The BICEP-Keck collaboration has been leading the search for B-modes with a suite of small aperture telescopes (SATs) operating from the South Pole. This talk will introduce the physics behind B-modes, the signals that are being pursued and the cutting-edge technologies behind these telescopes. Today BICEP-Array is fielding four SATs which will measure the polarized CMB and associated foregrounds to unprecedented precision, charting the way for CMB-Stage 4. CMB-Stage 4 is a major collaborative undertaking to comprehensively map the CMB-sky and will set the ultimate standards for PGW detection with B-mode surveys. See talks by Hui on latest groundbreaking BICEP/Keck results, Yu for introduction to BICEP-Array and multicomponent analysis, Cheshire on performance of BICEP-Array and the future reach of the program and Fatigoni on Polar atmospheric monitoring for improving CMB sensitivities.    

Improved Measurements of the Temperature and E-Mode Polarization of the CMB from 500 Square Degrees of Multi-Band SPTpol Data

We present the final analysis of the E-mode polarization angular auto-power spectrum (EE) and temperature-E-mode cross-power spectrum (TE) of the cosmic microwave background (CMB) from all four seasons of 500 deg² SPTpol observations, using both frequency bands available (150 GHz and 90 GHz). These measurements are the most sensitive to date of the EE and TE power spectra at multipole ℓ > ∼2000. We also present the best-fit cosmological parameter constraints.   

Improved constraints on primordial gravitational waves using BICEP/Keck observations

In this talk, I will present the latest analysis from the BICEP/Keck experiments. This result shows the tensor-to-scalar ratio r < 0.036 at 95% confidence with σ(r)=0.009, which is the tightest constraint to date on primordial gravitational waves.

Cosmic inflation was postulated to solve the horizon, flatness and monopole problems arise from the standard LCDM model. Inflation generically predicts the existence of primordial gravitational waves which would leave a unique degree-scale B-mode polarization pattern in the cosmic microwave background (CMB). If detected, this can serve as a probe to the early Universe and high energy physics inaccessible with existing particle accelerators. The BICEP/Keck experiments are a series of telescopes at the South Pole designed to search for this degree-scale B-mode signature in the CMB. Our latest release (BK18) includes new data collected through the 2018 season, and is the first to utilize observations from the 95GHz BICEP3 telescope.   

The BICEP Array CMB Polarimetry Experiment and Multicomponent Analysis

This talk gives an overview of the BICEP Array experimental design and its scientific goals with an emphasis on Galactic foreground measurement and separation. The BICEP Array is the latest experiment in the BICEP/Keck series, which leads the search for inflationary gravitational waves by measuring the characteristic "B-mode" polarization pattern. The full array will deploy over 30,000 detectors across six frequency bands to map the polarization of the CMB and separate out Galactic foregrounds.  This talk will cover how the search for signatures of cosmic inflation informed the instrument and observation strategy design. I will motivate the need for multicomponent analysis and discuss current and planned strategies for removing Galactic foregrounds, which limit the ability of CMB polarimetry experiments to constrain primordial gravitational waves from inflation. Special attention will be paid to the high-frequency receiver operating at 220/270GHz, which offers a unique window into the behavior of polarized Galactic dust and the Galactic magnetic field. 

See talks by Basu Thakur for an overview of the BICEP/Keck program and probing inflationary B-modes with small-aperture telescopes and Cheshire on deployment of the first BICEP Array receiver and the forecasting future BICEP/Keck sensitivity.   

High Resolution analysis of the South Pole Atmosphere for CMB observations

Maps of Precipitable Water Vapor (PWV) fluctuations in the South Pole Atmosphere are highly informative and suitable to study atmospheric noise leakage into Cosmic Microwave Background (CMB) data.

Cosmological B-Modes in the polarization of the Cosmic Microwave Background (CMB) can provide direct evidence for inflation. The Bicep/Keck Array (BK) program has published the most stringent constraints on inflation to date, and Bicep Array (BA), the newest stage of the experiment, is projected to reach a level of sensitivity one order of magnitude lower than the tightest constraint today. Even as this big detector improvement increases sensitivity, atmospheric fluctuations in space and time limit our ability to explore large angular scales. We have carried out a high temporal and spatial resolution measurements of the atmospheric brightness fluctuations at the South Pole using a Water Vapor Radiometer (WVR) that is scanning the sky in azimuth twice per minute at an elevation that matches the center of BK maps. We have produced atmospheric maps that are suitable for cleaning CMB data.