Sparse component separation for accurate CMB map estimation

The Cosmological Microwave Background (CMB) is of premier importance for the cosmologists to study the birth of our universe. Unfortunately, most CMB experiments such as COBE, WMAP or Planck do not provide a direct measure of the cosmological signal; CMB is mixed up with galactic foregrounds and point sources. For the sake of scientific exploitation, measuring the CMB requires extracting several different astrophysical components (CMB, Sunyaev-Zel'dovich clusters, galactic dust) form multi-wavelength observations. Mathematically speaking, the problem of disentangling the CMB map from the galactic foregrounds amounts to a component or source separation problem. In the field of CMB studies, a very large range of source separation methods have been applied which all differ from each other in the way they model the data and the criteria they rely on to separate components. Two main difficulties are i) the instrument's beam varies across frequencies and ii) the emission laws of most astrophysical components vary across pixels. This paper aims at introducing a very accurate modeling of CMB data, based on sparsity, accounting for beams variability across frequencies as well as spatial variations of the components' spectral characteristics. Based on this new sparse modeling of the data, a sparsity-based component separation method coined Local-Generalized Morphological Component Analysis (L-GMCA) is described. Extensive numerical experiments have been carried out with simulated Planck data. These experiments show the high efficiency of the proposed component separation methods to estimate a clean CMB map with a very low foreground contamination, which makes L-GMCA of prime interest for CMB studies.Comment: submitted to A&

The networked character of migration and transnationalism

Acknowledgement of the prominent role of social networks in migration studies marked a significant departure from earlier studies, suggesting that social networks determine migration decisions, trajectories, and outcomes. While social network analytical tools have not always been used in empirical investigations of migratory phenomena, studies on migration that use relational approaches also show an inherent network thinking. In this paper, we review the state of the art of the literature on migration and social networks, highlighting the advances made by empirical research using network thinking, particularly in different stages of migration and for operationalizing transnational phenomena related to migration. Based on this review, we detect the role of networks in different stages of migration, andwe reflect on the remaining challenges for future research regarding the role of social networks within migration scholarship

The networked character of migration and transnationalism

Acknowledgement of the prominent role of social networks in migration studies marked a significant departure from earlier studies, suggesting that social networks determine migration decisions, trajectories, and outcomes.While social network analytical tools have not always been used in empirical investigations of migratory phenomena, studies on migration that use relational approaches also show an inherent network thinking. In this paper, we review the state of the art of the literature on migration and social networks, highlighting the advances made by empirical research using network thinking, particularly in different stages of migration and for operationalizing transnational phenomena related to migration. Based on this review, we detect the role of networks in different stages of migration, and we reflect on the remaining challenges for future research regarding the role of social networks within migration scholarship

Isospin breaking in the nucleon mass and the sensitivity of β decays to new physics

We discuss the consequences of the approximate conservation of the vector and axial currents for the hadronic matrix elements appearing in β decay if nonstandard interactions are present. In particular, the isovector (pseudo)scalar charge gS(P) of the nucleon can be related to the difference (sum) of the nucleon masses in the absence of electromagnetic effects. Using recent determinations of these quantities from phenomenological and lattice QCD studies we obtain the accurate values gS=1.02(11) and gP=349(9) in the modified minimal subtraction scheme at μ=2  GeV. The consequences for searches of nonstandard scalar interactions in nuclear β decays are studied, finding for the corresponding Wilson coefficient εS=0.0012(24) at 90% C.L., which is significantly more stringent than current LHC bounds and previous low-energy bounds using less precise gS values. We argue that our results could be rapidly improved with updated computations and the direct calculation of certain ratios in lattice QCD. Finally, we discuss the pion-pole enhancement of gP, which makes β decays much more sensitive to nonstandard pseudoscalar interactions than previously thought