# Polarization angle accuracy for future CMB experiments. The COSMOCal project and its prototype in the 1mm band

**Authors:** A. Ritacco, L. Bizzarri, F. Boulanger, M. Pérault, J. Aumont, F. Bouchet, M. Calvo, A. Catalano, D. Darson, F. X. Désert, J. Errard, A. Feret, J. F. Macías-Pérez, B. Maffei, A. Monfardini, L. Montier, M. Murgia, P. Morfin, F. Nati, G. Pisano  
**arXiv:** [2311.08307](https://arxiv.org/abs/2311.08307)  
**Date:** 2023-11-14  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2311.08307v1/

## Key points

- The Cosmic Microwave Background (CMB) radiation provides insights into the early Universe and cosmological theories.
- Detecting B-modes in the CMB presents challenges in calibration and foreground modeling.
- The COSMOCal project aims to enhance the accuracy of polarization angle calibration in CMB experiments.
- An artificial source emitting radiation within 20-350 GHz is being constructed as an absolute calibrator.
- Feasibility study underway to determine if placing the source in geostationary orbit is possible.
- Prototype being built to test precision and stability in recovering polarization signals within the 1 mm band.
- High-resolution experiments with NIKA2 camera at IRAM 30m telescope will be used to evaluate prototype effectiveness.
- Once calibrated with accuracy better than 0.1 degrees, system will observe astrophysical sources like Crab nebula for absolute calibration of CMB experiments.
- Improved accuracy of measuring polarization angles will overcome challenges related to calibration and foreground modeling.
- This advancement will contribute to understanding inflationary models and support cosmological theories.

## Summary

The Cosmic Microwave Background (CMB) radiation provides valuable insights into the early Universe and allows for precise investigations of fundamental cosmological theories. However, detecting B-modes in the CMB, which are predicted by theoretical models of inflation, presents significant challenges in terms of calibration and foreground modeling. To address this issue, the COSMOCal (COsmic Survey of Millimeter wavelengths Objects for CMB experiments Calibration) project aims to enhance the accuracy of the absolute calibration of the polarization angle $\psi$ in current and future CMB experiments. The concept involves constructing a highly accurate artificial source that emits radiation within the frequency range of 20-350 GHz. This artificial source would serve as an absolute calibrator for various polarization facilities on Earth. A feasibility study is currently underway to determine if placing this artificial source in geostationary orbit, where it would be in the far field for all telescopes on Earth, is feasible. Simultaneously, ongoing hardware work is focused on building a prototype to test its precision and stability in recovering polarization signals within the 1 mm band (220-300 GHz). To evaluate the effectiveness of this prototype, high-resolution experiments such as the NIKA2 camera at the IRAM 30m telescope will be deployed. Once carefully calibrated with an accuracy better than 0.1 degrees ($\Delta\psi$ < 0.1 degrees), this system will be used to observe astrophysical sources like the Crab nebula which is considered one of the best candidates in sky for absolute calibration of CMB experiments. By improving accuracy of measuring polarization angles in CMB experiments through COSMOCal researchers hope to overcome challenges related to calibration and foreground modeling. This advancement will contribute significantly to our understanding of inflationary models and provide more robust support for fundamental cosmological theories.