Scientific rationale

Current and next-generation Cosmic Microwave Background (CMB) polarization experiments will make sensitive maps of the polarized emission from the Milky Way. These data provide a multi-frequency window into the polarized Galactic sky, and can be used to study the structure and evolution of the magnetic interstellar medium, star formation, turbulence, the composition of interstellar dust, and many more open questions. Also, very importantly, the detailed characterization of this Galactic "foreground" emission is crucial for enabling precision cosmological measurements with the CMB, in particular the search for the B-mode polarization signal imprinted by Gravitational Waves in the Early Universe.This endeavor is becoming even more demanding as CMB experiments are currently pushing the limit on the tensor-to-scalar ratio to values close to r=0.01, while over the next decade space and ground based measurements are targeting r=0.001. This workshop aims at bringing together experts in interstellar medium (ISM) science and in CMB foreground characterization. Facilitating discussion between these communities is necessary to realize the full potential of these rich data.

This workshop is the second of the Core to Core CMB Workshop series, which started with the "CMB systematics and calibration focus workshop" held remotely in November 2020, and aims to cover different aspects related with the CMB field. In this case the focus is on CMB foregrounds, following the same spirit as a "previous conference organised in Tenerife in 2018". The goals are to review existing Galactic emission models and to discuss improvements in the light of existing and future data and of the requirements for future B-mode missions, with emphasis on strengthening the obvious connection between CMB foregrounds and Galactic astrophysics. The workshop will revolve around topics organised in different sessions:

• Data landscape in the microwave and beyond
• The structure of the Galactic Magnetic Field
• Galactic science with CMB experiment data
• Modelling of the Galactic emission components and forecast
• Component separation and foreground mitigation
• Synergy with hot topics, cosmic-birefringence, 3D stellar distribution unveiled by GAIA, etc.

Invited speakers will present general talks covering the status all these topics, followed by contributed talks and supplemented by poster sessions. Sufficient time will be allocated to discussions, including a final session where participants should outline future directions and summarise the main conclusions.