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Challenges for the forthcoming CMB polarization experiments

Sede A. Riccò Via Santa Sofia 78, Catania

One of the major challenges in the context of the Cosmic Microwave Background (CMB) radiation is to detect a polarization pattern, the so called B-modes of CMB polarization, that are thought to be directly linked to the space-time fluctuations present in the Universe at the very first instants of life. To date, several challenges have prevented to detect the B-modes partly because of the lower sensitivity of the detectors. Our own Galaxy is observed in this context as a foreground contamination. However the awareness of improving the modeling of its polarized emission has been constantly increase not only to assess the cosmological signals but also to provide new insights onto the Galactic magnetic field probed with the Galactic polarized emissions, e.g. synchrotron and thermal dust. This is particularly relevant in order to better characterize the foreground contamination for future CMB experiments (e.g. SO, LiteBIRD, CMB-S4 ), where unprecedented polarization sensitivities are expected to be achieved in the coming decades.

Neural Networs: new models for recovering the Cosmic Microwave Background

Sede A. Riccò Via Santa Sofia 78, Catania

The Cosmic Microwave Background, the relic emission from the primordial Universe, is one of the most important observables in Cosmology. Its recovery is generally carried out by parametric and (semi) blind methods after removing several Galactic and extragalactic emissions. However, in order to take into account their non-linear behaviors, Machine Learning approaches such Neural Networks seem to be promising for that task. In this talk, I will describe how they begin to be an alternative and reliable methods for recovering the Cosmic Microwave Background.

Non-standard signatures from CMB polarisation with an insight into the new technological challenges

Sede A. Riccò Via Santa Sofia 78, Catania

In this seminar, I will focus on non-standard signatures from CMB polarisation that may indicate the existence of new phenomena beyond the standard models of cosmology and particle physics, from both theoretical and observational perspectives. ESA's Planck mission has observed CMB temperature anisotropies at the cosmic variance limit, but polarisation remains to be further investigated. CMB polarisation data are important not only because they contribute to provide tighter constraints on cosmological parameters but also because they allow the study of physical processes that would be excluded if only the CMB temperature maps were considered. I use polarisation data into account to assess the statistical significance of the anomalies currently observed only in the CMB temperature map, and to constrain the Cosmic Birefringence (CB) effect, which is expected in parity-violating extensions of the standard electromagnetism.
Measuring CMB polarisation is technically challenging because the polarised signal is much fainter than the temperature signal, and accurate polarisation estimates require exquisite control of systematic effects. To investigate the impact of spurious signals in upcoming CMB polarisation experiments, I present a study of the interplay between half-wave plate (HWP) non-idealities and the beams of the instrument for the next generation of CMB experiments, with an insight into how this instrumental contamination affects the measurement of the cosmic birefringence effect.

Elucidating diffuse Galactic synchrotron emission for precision 21cm and CMB cosmology

Sede A. Riccò Via Santa Sofia 78, Catania

The next generation of Cosmic Microwave Background experiments are poised to probe the inflationary period of the Universe through the measurement of primordial B-modes, whilst 21cm experiments are observing the reionization history of the early Universe and formation of Large-Scale Structure through the mapping of neutral hydrogen. These two complementary fields span the radio to microwave frequency regimes and share a pivotal data reduction task: foreground component separation.

Diffuse Galactic synchrotron emission is the dominant foreground for arcmin/degree scale cosmological surveys operating across MHz frequencies in intensity, and at all frequencies under 60 GHz in polarised intensity. In this talk I will present measurements of the synchrotron spectral index and curvature between 73 MHz and 1 GHz through the combined use of pilot MeerKLASS, Haslam, Maipu/MU and LWA data. I will discuss the advances that can be made to component separation algorithms thanks to more sophisticated foreground emission modelling and will present a spatially complex, all-sky model of the synchrotron spectral index formed using convolutional neural networks trained on sets of both high- and low-resolution empirical data. Such advances will, and already are, expanding our understanding of the spatial and spectral form of this complex emission; ameliorating component separation for both CMB and 21cm intensity mapping experiments.