Periodic Reporting for period 2 - NEUCosmoS (The New era of EUropean CMB Cosmology with the South Pole Telescope)
Reporting period: 2023-03-01 to 2024-08-31
NEUCosmoS is a project funded by an ERC consolidator grant. The goal of NEUCosmoS is to unravel some of the most puzzling inconsistencies that are challenging the standard model of cosmology (ΛCDM). The biggest mystery is the conflicting measurements of the universe's expansion rate, known as the Hubble constant (H0). Early-time probes, such as the Cosmic Microwave Background (CMB) radiation, suggest a slower expansion than measurements from late-time probes, such as Supernovae Ia calibrated through Cepheids. This unexpected inconsistency is also known as the Hubble tension. Additional discrepancies are also present in the amplitude of matter perturbations (σ8) and in other fundamental parameters, such as the curvature of the universe, as measured by different cosmological probes. If confirmed, these mismatches could force us to rethink our understanding of physics.
To address these discrepancies, NEUCosmoS is developing a powerful pipeline to extract some of the most precise cosmological information from one of the forefront CMB experiments: the South Pole Telescope 3G (SPT-3G). SPT-3G is mapping the CMB temperature and polarisation at small angular scales with unprecedented precision over 25% of the sky. It is opening an entirely new window in CMB cosmology.
However, this statistical power is useless without an analysis pipeline able to guarantee robustness against spurious systematic effects.The NEUCosmoS team is building a robust pipeline upon the group’s Planck satellite experience and tools, adapting them to the new challenge. This is allowing the team to lead the interpretation of current and future hints of new physics in a reliable way. The full SPT-3G dataset is expected to improve by a factor of two the constraining capability of the Planck satellite on cosmological parameters. This will potentially shed light on the current cosmological tensions and yield original discoveries on its own.
The work performed by the NEUCosmoS team will also pave the way to a future contribution by Europe to the next-generation of CMB experiments.
To address these discrepancies, NEUCosmoS is developing a powerful pipeline to extract some of the most precise cosmological information from one of the forefront CMB experiments: the South Pole Telescope 3G (SPT-3G). SPT-3G is mapping the CMB temperature and polarisation at small angular scales with unprecedented precision over 25% of the sky. It is opening an entirely new window in CMB cosmology.
However, this statistical power is useless without an analysis pipeline able to guarantee robustness against spurious systematic effects.The NEUCosmoS team is building a robust pipeline upon the group’s Planck satellite experience and tools, adapting them to the new challenge. This is allowing the team to lead the interpretation of current and future hints of new physics in a reliable way. The full SPT-3G dataset is expected to improve by a factor of two the constraining capability of the Planck satellite on cosmological parameters. This will potentially shed light on the current cosmological tensions and yield original discoveries on its own.
The work performed by the NEUCosmoS team will also pave the way to a future contribution by Europe to the next-generation of CMB experiments.
-- Early Observations from SPT-3G 2018.
In its first four months of operation in 2018, SPT-3G, using only half of its focal plane, collected data yielding very deep observations of the cosmic microwave background (CMB) power spectra at small scales. The estimated cosmological parameters from this data are consistent with those found by Planck. We measured a lower Hubble constant value compared to measurements from supernovae Ia calibrated with Cepheids. To ensure the robustness of these findings, we implemented several innovative techniques, including blinding the analysis, performing extensive consistency tests, and using machine learning emulators to speed up cosmological parameter estimations.
-- Enhanced Observation Strategy.
We helped develop a new observation strategy for SPT-3G. The survey now includes not only the originally planned winter field (1500 square degrees) but also summer fields (3500 square degrees) and wide fields (6000 square degrees). This approach will produce some of the deepest CMB observations in temperature and polarisation across a substantial portion of the sky (25%). The complete dataset is expected to improve constraints on cosmological parameters by a factor of two compared to the Planck satellite, potentially shedding light on unresolved tensions in cosmology, such as the Hubble tension, and potentially revealing signatures of new physics.
-- Methodological Advancements.
We have made innovative contributions to the analysis methods used in SPT-3G. We pioneered the calculation of the exact covariance matrix for CMB power spectra on the observed cut sky and proposed a new, accurate approximation for faster calculations. Additionally, we developed the necessary tools to perform the SPT-3G analysis on the curved sky, moving beyond the traditional flat sky approximation.
-- Future Analysis Tools.
We developed "candl," a fully differentiable likelihood code for the next release of SPT-3G data. Combined with a differentiable theory code, candl enables much faster parameter inference, systematic effect projections, and accurate, rapid forecasting. This significantly accelerates data consistency tests, leading to more robust results.
-- Exploring the Hubble Tension.
We have employed the 2018 SPT-3G data, along with data from other probes, to constrain various models proposed to explain the Hubble tension. This analysis has ruled out some previously popular models, leaving only a few viable candidates, such as the variation of electron mass in a curved universe and early dark energy.
-- Dissemination and Outreach.
The team has actively disseminated its findings. We have published more than 20 papers. We have reported our results in over 40 talks and seminars at international conferences and institutes. We have organized conferences, held a press release, conducted outreach through social media (#neucosmos on Twitter/X), through a website https://neucosmos.cnrs.fr/(opens in new window) and engaged with the general public.
In its first four months of operation in 2018, SPT-3G, using only half of its focal plane, collected data yielding very deep observations of the cosmic microwave background (CMB) power spectra at small scales. The estimated cosmological parameters from this data are consistent with those found by Planck. We measured a lower Hubble constant value compared to measurements from supernovae Ia calibrated with Cepheids. To ensure the robustness of these findings, we implemented several innovative techniques, including blinding the analysis, performing extensive consistency tests, and using machine learning emulators to speed up cosmological parameter estimations.
-- Enhanced Observation Strategy.
We helped develop a new observation strategy for SPT-3G. The survey now includes not only the originally planned winter field (1500 square degrees) but also summer fields (3500 square degrees) and wide fields (6000 square degrees). This approach will produce some of the deepest CMB observations in temperature and polarisation across a substantial portion of the sky (25%). The complete dataset is expected to improve constraints on cosmological parameters by a factor of two compared to the Planck satellite, potentially shedding light on unresolved tensions in cosmology, such as the Hubble tension, and potentially revealing signatures of new physics.
-- Methodological Advancements.
We have made innovative contributions to the analysis methods used in SPT-3G. We pioneered the calculation of the exact covariance matrix for CMB power spectra on the observed cut sky and proposed a new, accurate approximation for faster calculations. Additionally, we developed the necessary tools to perform the SPT-3G analysis on the curved sky, moving beyond the traditional flat sky approximation.
-- Future Analysis Tools.
We developed "candl," a fully differentiable likelihood code for the next release of SPT-3G data. Combined with a differentiable theory code, candl enables much faster parameter inference, systematic effect projections, and accurate, rapid forecasting. This significantly accelerates data consistency tests, leading to more robust results.
-- Exploring the Hubble Tension.
We have employed the 2018 SPT-3G data, along with data from other probes, to constrain various models proposed to explain the Hubble tension. This analysis has ruled out some previously popular models, leaving only a few viable candidates, such as the variation of electron mass in a curved universe and early dark energy.
-- Dissemination and Outreach.
The team has actively disseminated its findings. We have published more than 20 papers. We have reported our results in over 40 talks and seminars at international conferences and institutes. We have organized conferences, held a press release, conducted outreach through social media (#neucosmos on Twitter/X), through a website https://neucosmos.cnrs.fr/(opens in new window) and engaged with the general public.
We are actively working on the next SPT-3G data release, which will be based on two years of winter and summer field observations obtained with the full focal plane. This significantly enhanced dataset will provide groundbreaking constraints on cosmological parameters, achieving sensitivity comparable to the Planck satellite. The analysis of wide field data is also underway. The complete SPT-3G dataset is expected to improve Planck constraints by a factor of two, potentially yielding revolutionary insights into the standard cosmological model and its extensions.