SU(3)-guided Realistic Nucleon-nucleon Interactions for Large-scale Calculations

We examine nucleon-nucleon realistic interactions, based on their SU(3) decomposition to SU(3)-symmetric components. We find that many of these interaction components are negligible, which, in turn, allows us to identify a subset of physically relevant components that are sufficient to describe the structure of low-lying states in $^{12}$C and related observables, such as excitation energies, electric quadrupole transitions and rms radii. We find that paring the interaction down to half of the SU(3)-symmetric components or more yields results that practically coincide with the corresponding ab initio calculations with the full interaction. In addition, we show that while various realistic interactions differ in their SU(3) decomposition, their renormalized effective counterparts exhibit a striking similarity and composition that can be linked to dominant nuclear features such as deformation, pairing, clustering, and spin-orbit effect.Comment: 9 pages, 7 figure

High contrast D1_{1} line electromagnetically induced transparency in nanometric-thin rubidium vapor cell

Electromagnetically induced transparency (EIT) on atomic D$_{1}$ line of rubidium is studied using a nanometric-thin cell with atomic vapor column length in the range of L= 400 - 800 nm. It is shown that the reduction of the cell thickness by 4 orders as compared with an ordinary cm-size cell still allows to form an EIT resonance for $L= \lambda$ ($\lambda =794$ nm) with the contrast of up to 40%. Remarkable distinctions of EIT formation in nanometric-thin and ordinary cells are demonstrated. Despite the Dicke effect of strong spectral narrowing and increase of the absorption for $L=$ $\lambda /2$, EIT resonance is observed both in the absorption and the fluorescence spectra for relatively low intensity of the coupling laser. Well resolved splitting of the EIT resonance in moderate magnetic field for $L=$ $\lambda$ can be used for magnetometry with nanometric spatial resolution. The presented theoretical model well describes the observed results.Comment: Submitted to Applied Physics B: Lasers and Optics, 9 pages, 10 figure

Machine learning approach to pattern recognition in nuclear dynamics from the ab initio symmetry-adapted no-core shell model

A novel machine learning approach is used to provide further insight into atomic nuclei and to detect orderly patterns amidst a vast data of large-scale calculations. The method utilizes a neural network that is trained on ab initio results from the symmetry-adapted no-core shell model (SA-NCSM) for light nuclei. We show that the SA-NCSM, which expands ab initio applications up to medium-mass nuclei by using dominant symmetries of nuclear dynamics, can reach heavier nuclei when coupled with the machine learning approach. In particular, we find that a neural network trained on probability amplitudes for $s$-and $p$-shell nuclear wave functions not only predicts dominant configurations for heavier nuclei but in addition, when tested for the $^{20}$Ne ground state, it accurately reproduces the probability distribution. The nonnegligible configurations predicted by the network provide an important input to the SA-NCSM for reducing ultra-large model spaces to manageable sizes that can be, in turn, utilized in SA-NCSM calculations to obtain accurate observables. The neural network is capable of describing nuclear deformation and is used to track the shape evolution along the $^{20-42}$Mg isotopic chain, suggesting a shape-coexistence that is more pronounced toward the very neutron-rich isotopes. We provide first descriptions of the structure and deformation of $^{24}$Si and $^{40}$Mg of interest to x-ray burst nucleosynthesis, and even of the extremely heavy nuclei such as $^{166,168}$Er and $^{236}$U, that build upon first principles considerations.Comment: 10 pages, 9 figure

Peculiarities of sub-barrier fusion with quantum diffusion approach

With the quantum diffusion approach the unexpected behavior of fusion cross section, angular momentum, and astrophysical S-factor at sub-barrier energies has been revealed. Out of the region of short-range nuclear interaction and action of friction at turning point the decrease rate of the cross section under the barrier becomes smaller. The calculated results for the reactions with spherical nuclei are in a good agreement with the existing experimental data.Comment: 11 pages, 5 figure

Sub-barrier capture with quantum diffusion approach: actinide-based reactions

With the quantum diffusion approach the behavior of capture cross sections and mean-square angular momenta of captured systems are revealed in the reactions with deformed nuclei at subbarrier energies. The calculated results are in a good agreement with existing experimental data. With decreasing bombarding energy under the barrier the external turning point of the nucleusnucleus potential leaves the region of short-range nuclear interaction and action of friction. Because of this change of the regime of interaction, an unexpected enhancement of the capture cross section is expected at bombarding energies far below the Coulomb barrier. This effect is shown its worth in the dependence of mean-square angular momentum of captured system on the bombarding energy. From the comparison of calculated and experimental capture cross sections, the importance of quasifission near the entrance channel is shown for the actinide-based reactions leading to superheavy nuclei.Comment: 11 pages, 16 figures, Regular Articl

Clustering and α -capture reaction rate from ab initio symmetry-adapted descriptions of Ne 20

We introduce a new framework for studying clustering and for calculating α partial widths using ab initio wave functions. We demonstrate the formalism for Ne20, by calculating the overlap between the O16+α cluster configuration and states in Ne20 computed in the abinitio symmetry-adapted no-core shell model. We present spectroscopic amplitudes and spectroscopic factors, and compare those to no-core symplectic shell-model results in larger model spaces, to gain insight into the underlying physics that drives α clustering. Specifically, we report on the α partial width of the lowest 1- resonance in Ne20, which is found to be in good agreement with experiment. We also present first no-core shell-model estimates for asymptotic normalization coefficients for the ground state, as well as for the first excited 4+ state in Ne20 that lies in a close proximity to the α+16O threshold. This outcome highlights the importance of correlations for developing cluster structures and for describing α widths. The widths can then be used to calculate α-capture reaction rates for narrow resonances of interest to astrophysics. We explore the reaction rate for the α-capture reaction O16(α,γ)20Ne at astrophysically relevant temperatures and determine its impact on simulated x-ray burst abundances

CASSIS: The Cornell Atlas of Spitzer/Infrared Spectrograph Sources. II. High-resolution observations

The Infrared Spectrograph (IRS) on board the Spitzer Space Telescope observed about 15,000 objects during the cryogenic mission lifetime. Observations provided low-resolution (R~60-127) spectra over ~5-38um and high-resolution (R~600) spectra over ~10-37um. The Cornell Atlas of Spitzer/IRS Sources (CASSIS) was created to provide publishable quality spectra to the community. Low-resolution spectra have been available in CASSIS since 2011, and we present here the addition of the high-resolution spectra. The high-resolution observations represent approximately one third of all staring observations performed with the IRS instrument. While low-resolution observations are adapted to faint objects and/or broad spectral features (e.g., dust continuum, molecular bands), high-resolution observations allow more accurate measurements of narrow features (e.g., ionic emission lines) as well as a better sampling of the spectral profile of various features. Given the narrow aperture of the two high-resolution modules, cosmic ray hits and spurious features usually plague the spectra. Our pipeline is designed to minimize these effects through various improvements. A super sampled point-spread function was created in order to enable the optimal extraction in addition to the full aperture extraction. The pipeline selects the best extraction method based on the spatial extent of the object. For unresolved sources, the optimal extraction provides a significant improvement in signal-to-noise ratio over a full aperture extraction. We have developed several techniques for optimal extraction, including a differential method that eliminates low-level rogue pixels (even when no dedicated background observation was performed). The updated CASSIS repository now includes all the spectra ever taken by the IRS, with the exception of mapping observations