Quantum fluctuations and stability of tetrahedral deformations in atomic nuclei

The possible existence of stable axial octupole and tetrahedral deformations is investigated in $^{80}$Zr and $^{98}$Zr. HFBCS calculations with parity projection have been performed for various parametrizations of the Skyrme energy functional. The correlation and excitation energies of negative parity states associated with shape fluctuations have been obtained using the generator coordinate method (GCM). The results indicate that in these nuclei both the axial octupole and tetrahedral deformations are of dynamic character and possess similar characteristics. Various Skyrme forces give consistent results as a function of these two octupole degrees of freedom both at the mean-field level as well as for configuration mixing calculations.Comment: 8 pages, 4 figures, submitted to IJMP

Real time description of fission

Using the time-dependent superfluid local density approximation, the dynamics of fission is investigated in real time from just beyond the saddle to fully separated fragments. Simulations produced in this fully microscopic framework can help to assess the validity of the current approaches to fission, and to obtain estimate of fission observables. In this contribution, we concentrate on general aspects of fission dynamics.Comment: Proceedings of the "15th Varenna Conference on Nuclear Reaction Mechanisms," Varenna, Italy, June 201

Nuclear Fission: from more phenomenology and adjusted parameters to more fundamental theory and increased predictive power

Two major recent developments in theory and computational resources created the favorable conditions for achieving a microscopic description of nuclear fission almost eighty years after its discovery in 1939 by Hahn and Strassmann (1930). The first major development was in theory, the extension of the Time-Dependent Density Functional Theory (TDDFT) to superfluid fermion systems. The second development was in computing, the emergence of powerful enough supercomputers capable of solving the complex systems of equations describing the time evolution in three dimensions without any restrictions of hundreds of strongly interacting nucleons. Even though the available nuclear energy density functionals (NEDFs) are phenomenological still, their accuracy is improving steadily and the prospects of being able to perform calculations of the nuclear fission dynamics and to predict many properties of the fission fragments, otherwise not possible to extract from experiments, are within reach, all without making recourse anymore to uncontrollable assumptions and simplified phenomenological models.Comment: 6 pages, account of invited talk given at FUSION17, Hobart, Tasmania, February 20-24, 201

Hartree-Fock-Bogolyubov calculations for nuclei with tetrahedral deformation

Hartree-Fock-Bogolyubov solutions corresponding to the tetrahedral deformation are found in six tetrahedrally doubly-magic nuclei. Values of the beta32 deformation, depths of the tetrahedral minima, and their energies relative to the co-existing quadrupole minima are determined for several versions of the Skyrme force. Reduction of the tetrahedral deformation energies by pairing correlations is quantitatively analysed. In light nuclei, shallow tetrahedral minima are found to be the lowest in energy, while in heavy nuclei, the minima are deeper but appear at a few MeV of excitation.Comment: 6 LaTeX pages, 2 PostScript figures, presented at the XII Nuclear Physics Workshop, 21-25 September, Kazimierz Dolny, Polan

Microscopically-based energy density functionals for nuclei using the density matrix expansion: Implementation and pre-optimization

In a recent series of papers, Gebremariam, Bogner, and Duguet derived a microscopically based nuclear energy density functional by applying the Density Matrix Expansion (DME) to the Hartree-Fock energy obtained from chiral effective field theory (EFT) two- and three-nucleon interactions. Due to the structure of the chiral interactions, each coupling in the DME functional is given as the sum of a coupling constant arising from zero-range contact interactions and a coupling function of the density arising from the finite-range pion exchanges. Since the contact contributions have essentially the same structure as those entering empirical Skyrme functionals, a microscopically guided Skyrme phenomenology has been suggested in which the contact terms in the DME functional are released for optimization to finite-density observables to capture short-range correlation energy contributions from beyond Hartree-Fock. The present paper is the first attempt to assess the ability of the newly suggested DME functional, which has a much richer set of density dependencies than traditional Skyrme functionals, to generate sensible and stable results for nuclear applications. The results of the first proof-of-principle calculations are given, and numerous practical issues related to the implementation of the new functional in existing Skyrme codes are discussed. Using a restricted singular value decomposition (SVD) optimization procedure, it is found that the new DME functional gives numerically stable results and exhibits a small but systematic reduction of our test $\chi^2$ function compared to standard Skyrme functionals, thus justifying its suitability for future global optimizations and large-scale calculations.Comment: 17 pages, 6 figure

Fifty-fold improvement in the number of quantum degenerate fermionic atoms

We have produced a quantum degenerate Li-6 Fermi gas with up to 7 x 10^7 atoms, an improvement by a factor of fifty over all previous experiments with degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic Na-23 in the F=2, upper hyperfine ground state. We have also achieved Bose-Einstein condensation of F=2 sodium atoms by direct evaporation

Boson Stars as Gravitational Lenses

We discuss boson stars as possible gravitational lenses and study the lensing effect by these objects made of scalar particles. The mass and the size of a boson star may vary from an individual Newtonian object similar to the Sun to the general relativistic size and mass of a galaxy close to its Schwarzschild radius. We assume boson stars to be transparent which allows the light to pass through them though the light is gravitationally deflected. We assume boson stars of the mass $M = 10^{10}M_\odot$ to be on non-cosmological distance from the observer. We discuss the lens equation for these stars as well as the details of magnification. We find that there are typically three images of a star but the deflection angles may vary from arcseconds to even degrees. There is one tangential critical curve (Einstein ring) and one radial critical curve for tangential and radial magnification, respectively. Moreover, the deflection angles for the light passing in the gravitational field of boson stars can be very large (even of the order of degrees) which reflects the fact they are very strong relativistic objects. We also propose a suitable formula for the lens equation for such large deflection angles, and with the reservation that large deflection angle images are highly demagnified but in the area of the tangential critical curve, their existence may help in observational detection of suitable lenses possessing characteristic features of boson stars which could also serve as a direct evidence for scalar fields in the universe.Comment: accepted by Astrophys. J., 31 pages, AASTeX, 6 figure

Radio-Frequency Spectroscopy of Ultracold Fermions

Radio-frequency techniques were used to study ultracold fermions. We observed the absence of mean-field "clock" shifts, the dominant source of systematic error in current atomic clocks based on bosonic atoms. This is a direct consequence of fermionic antisymmetry. Resonance shifts proportional to interaction strengths were observed in a three-level system. However, in the strongly interacting regime, these shifts became very small, reflecting the quantum unitarity limit and many-body effects. This insight into an interacting Fermi gas is relevant for the quest to observe superfluidity in this system.Comment: 6 pages, 6 figure