Stochastic approach to correlations beyond the mean field with the Skyrme interaction

Large-scale calculation based on the multi-configuration Skyrme density functional theory is performed for the light N=Z even-even nucleus, 12C. Stochastic procedures and the imaginary-time evolution are utilized to prepare many Slater determinants. Each state is projected on eigenstates of parity and angular momentum. Then, performing the configuration mixing calculation with the Skyrme Hamiltonian, we obtain low-lying energy-eigenstates and their explicit wave functions. The generated wave functions are completely free from any assumption and symmetry restriction. Excitation spectra and transition probabilities are well reproduced, not only for the ground-state band, but for negative-parity excited states and the Hoyle state.Comment: 4 pages, 1 figure, Talk at 2nd International Nuclear Physics Conference "Nuclear Structure and Dynamics", Opatija, Croatia, July 9 - 13, 201

Aspects of electron-phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO3_3 substrates

Mono- and multilayer FeSe thin films grown on SrTiO$_\mathrm{3}$ and BiTiO$_\mathrm{3}$ substrates exhibit a greatly enhanced superconductivity over that found in bulk FeSe. A number of proposals have been advanced for the mechanism of this enhancement. One possibility is the introduction of a cross-interface electron-phonon ($e$-$ph$) interaction between the FeSe electrons and oxygen phonons in the substrates that is peaked in the forward scattering (small ${\bf q}$) direction due to the two-dimensional nature of the interface system. Motivated by this, we explore the consequences of such an interaction on the superconducting state and electronic structure of a two-dimensional system using Migdal-Eliashberg theory. This interaction produces not only deviations from the expectations of conventional phonon-mediated pairing but also replica structures in the spectral function and density of states, as probed by angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and quasi-particle interference imaging. We also discuss the applicability of Migdal-Eliashberg theory for a situation where the \ep interaction is peaked at small momentum transfer and in the FeSe/STO system

Glauber-model analysis of total reaction cross sections for Ne, Mg, Si, and S isotopes with Skyrme-Hartree-Fock densities

A systematic analysis is made on the total reaction cross sections for Ne, Mg, Si, and S isotopes. The high-energy nucleus-nucleus collision is described based on the Glauber model. Using the Skyrme-Hartree-Fock method in the three-dimensional grid-space representation, we determine the nuclear density distribution for a wide range of nuclei self-consistently without assuming any spatial symmetry. The calculated total reaction cross sections consistently agree with the recent cross section data on Ne$+^{12}$C collision at 240$A$\,MeV, which makes it possible to discuss the radius and deformation of the isotopes. The total reaction cross sections for Mg$+^{12}$C, Si$+^{12}$C and S$+^{12}$C cases are predicted for future measurements. We also find that the high-energy cross section data for O, Ne, and Mg isotopes on a $^{12}$C target at around 1000\,$A$MeV can not be reproduced consistently with the corresponding data at 240\,$A$MeV.Comment: 10 pages, 14 figure

A Structure-Preserving Divide-and-Conquer Method for Pseudosymmetric Matrices

We devise a spectral divide-and-conquer scheme for matrices that are self-adjoint with respect to a given indefinite scalar product (i.e. pseudosymmetic matrices). The pseudosymmetric structure of the matrix is preserved in the spectral division, such that the method can be applied recursively to achieve full diagonalization. The method is well-suited for structured matrices that come up in computational quantum physics and chemistry. In this application context, additional definiteness properties guarantee a convergence of the matrix sign function iteration within two steps when Zolotarev functions are used. The steps are easily parallelizable. Furthermore, it is shown that the matrix decouples into symmetric definite eigenvalue problems after just one step of spectral division

Linear response calculation using the canonical-basis TDHFB with a schematic pairing functional

A canonical-basis formulation of the time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory is obtained with an approximation that the pair potential is assumed to be diagonal in the time-dependent canonical basis. The canonical-basis formulation significantly reduces the computational cost. We apply the method to linear-response calculations for even-even nuclei. E1 strength distributions for proton-rich Mg isotopes are systematically calculated. The calculation suggests strong Landau damping of giant dipole resonance for drip-line nuclei.Comment: 6 pages, 1 figure, INPC 2010 conference proceding

Configuration mixing calculation for complete low-lying spectra with the mean-field Hamiltonian

We propose a new theoretical approach to ground and low-energy excited states of nuclei extending the nuclear mean-field theory. It consists of three steps: stochastic preparation of many Slater determinants, the parity and angular momentum projection, and diagonalization of the generalized eigenvalue problems. The Slater determinants are constructed in the three-dimensional Cartesian coordinate representation capable of describing arbitrary shape of nuclei. We examine feasibility and usefulness of the method by applying the method with the BKN interaction to light 4N-nuclei, 12C, 16O, and 20Ne. We discuss difficulties of keeping linear independence for basis states projected on good parity and angular momentum and present a possible prescription.Comment: 12 pages, revtex