Stokes Inversion based on Convolutional Neural Networks

Spectropolarimetric inversions are routinely used in the field of Solar Physics for the extraction of physical information from observations. The application to two-dimensional fields of view often requires the use of supercomputers with parallelized inversion codes. Even in this case, the computing time spent on the process is still very large. Our aim is to develop a new inversion code based on the application of convolutional neural networks that can quickly provide a three-dimensional cube of thermodynamical and magnetic properties from the interpretation of two-dimensional maps of Stokes profiles. We train two different architectures of fully convolutional neural networks. To this end, we use the synthetic Stokes profiles obtained from two snapshots of three-dimensional magneto-hydrodynamic numerical simulations of different structures of the solar atmosphere. We provide an extensive analysis of the new inversion technique, showing that it infers the thermodynamical and magnetic properties with a precision comparable to that of standard inversion techniques. However, it provides several key improvements: our method is around one million times faster, it returns a three-dimensional view of the physical properties of the region of interest in geometrical height, it provides quantities that cannot be obtained otherwise (pressure and Wilson depression) and the inferred properties are decontaminated from the blurring effect of instrumental point spread functions for free. The code is provided for free on a specific repository, with options for training and evaluation.Comment: 18 pages, 14 figures, accepted for publication in Astronomy & Astrophysic

The Weak Decay of Hypernuclei

The nonmesonic weak decay of $\Lambda$ hypernuclei is studied in a shell model framework. A complete strangeness-changing weak $\Lambda N \to NN$ transition potential, based on one boson exchange, is constructed by including the exchange of the pseudoscalar mesons $\pi$, K, $\eta$ as well as the vector mesons $\rho, \omega$, and K$^*$, whose weak coupling constants are obtained from soft meson theorems and SU(6)$_w$. General expressions for nucleons in arbitrary shells are obtained. The transition matrix elements include realistic $\Lambda$N short-range correlations and NN final state interactions based on the Nijmegen baryon-baryon potential. The decay rates are found to be especially sensitive to the inclusion of the strange mesons, K and K$^*$, even though the role of kaon exchange is found to be reduced with recent couplings obtained from next-to-leading order Chiral Perturbation Theory. With the weak couplings used in this study the rates remain dominated by the pion-exchange mechanism since the contributions of heavier mesons either cancel each other or are suppressed by form factors and short-range correlations. The total decay rate therefore remains in agreement with present measurements. However, the partial rates which are even more sensitive to the inclusion of heavier mesons cannot be reconciled with the data. The proton asymmetry changes by 50% once heavier mesons are included and agrees with the available data.Comment: 70 pages, 8 figures, epsf.tex, revtex, submitted to Phys. Rev.

Recent results on the nonmesonic weak decay of hypernuclei within a one-meson-exchange model

We update our previous results for the nonmesonic decay of $^{12}_\Lambda$C and $^5_\Lambda$He. We pay special attention to the role played by Final State Intreractions on the decay observables. We follow a One-Meson-Exchange model which includes the exchange of the $\pi, \rho, K, K^*, \eta$ and $\omega$ mesons. We also present recent predictions for different observables concerning the decay of the doubly strange $^6_{\Lambda \Lambda}$He hypernucleus.Comment: 4 pages. Contribution to the Mesons and Light Nuclei'01 Conference, Prague, 2-6 July 200