Interstellar B-fields crossing inflation B-modes – BxB

The BxB project addresses outstanding questions at the heart of two rapidly advancing fields of astrophysics and cosmology: Galactic magnetism and Cosmic Microwave Background (CMB) polarization. BxB has three salient goals that involve cutting-edge research. Combining observations (of dust polarization, synchrotron emission and Faraday rotation), statistical data analysis and modelling, numerical simulations and theory, we will (1) build the first 3D model of the ordered magnetic field from the Sun to the Galactic halo, (2) achieve a statistical description of the turbulent component of the interstellar magnetic field, and (3) provide a physically motivated model of the multi-phase high latitude foregrounds needed to optimize separation of CMB and Galactic polarization, and reliably quantify uncertainties in the search for primordial gravitational waves. To achieve these goals in a timely manner, we propose a concerted research program stemming from a unique combination of data and team expertise. The BxB work plan will innovate and supersede state-of-the-art research in three research directions. (i) We will extend the 3D information on the nearby interstellar medium (ISM) derived from stellar observations including GAIA to the ordered magnetic field. (ii) We will introduce a novel approach in the analysis of data and numerical simulations to capture the hierarchy of coherent, anisotropic structures characterizing the structure of the magnetized ISM. (iii) We will provide the missing link between the astrophysics of polarized foregrounds and the quest for primordial CMB B-modes, a necessity highlighted in the French roadmap for CMB science. The BxB project will have a broad and lasting impact on Galactic magnetism, and an essential contribution to the on-going search for a signature of primordial gravitational waves from cosmic inflation.