1,463 research outputs found
Proton-neutron alignment in the yrast states of Ge and Ge
The Ge and Ge nuclei are studied by means of the shell model
with the extended Hamiltonian, which succeeds in reproducing
experimentally observed energy levels, moments of inertia and other properties.
The investigation using the reliable wave-functions predicts T=0, J=9
one-proton-one-neutron () alignment in the orbit, at high spins
(, and ) in these even-even nuclei. It
is shown that a series of the even- positive-parity yrast states (observed
up to for Ge) consists of the ground-state band and successive
three bands with different types of particle alignments (two-neutron, ,
two-proton-two-neutron) in the orbit.Comment: 4 pages, 5 figures, to be published in Pyhs. Rev.
Shape transition and oblate-prolate coexistence in N=Z fpg-shell nuclei
Nuclear shape transition and oblate-prolate coexistence in nuclei are
investigated within the configuration space (, ,
, and ). We perform shell model calculations for Zn,
Ge, and Se and constrained Hartree-Fock (CHF) calculations for
Zn, Ge, Se, and Kr, employing an effective pairing
plus quadrupole residual interaction with monopole interactions. The shell
model calculations reproduce well the experimental energy levels of these
nuclei. From the analysis of potential energy surface in the CHF calculations,
we found shape transition from prolate to oblate deformation in these
nuclei and oblate-prolate coexistence at Se. The ground state of
Se has oblate shape, while the shape of Zn and Ge are
prolate. It is shown that the isovector matrix elements between and
orbits cause the oblate deformation for Se, and four-particle
four-hole () excitations are important for the oblate configuration.Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev.
Extrapolation method in shell model calculations with deformed basis
An extrapolation method in shell model calculations with deformed basis is
presented, which uses a scaling property of energy and energy variance for a
series of systematically approximated wave functions to the true one. Such
approximated wave functions are given by variation-after-projection method
concerning the full angular momentum projection. This extrapolation needs
energy variance, which amounts to the calculation of expectation value of
square of Hamiltonian . We present the method to evaluate this
matrix element and show that large reduction of its numerical computation can
be done by taking an advantage of time-reversal symmetry. The numerical tests
are presented for shell calculations with a realistic residual
interaction.Comment: 5 pages, 2 figures, accepted for publication in Phys. Rev.
Stochastic extension of the Lanczos method for nuclear shell-model calculations with variational Monte Carlo method
We propose a new variational Monte Carlo (VMC) approach based on the Krylov
subspace for large-scale shell-model calculations. A random walker in the VMC
is formulated with the -scheme representation, and samples a small number of
configurations from a whole Hilbert space stochastically. This VMC framework is
demonstrated in the shell-model calculations of Cr and Zn, and we
discuss its relation to a small number of Lanczos iterations. By utilizing the
wave function obtained by the conventional particle-hole-excitation truncation
as an initial state, this VMC approach provides us with a sequence of
systematically improved results.Comment: 5 pages, 4 figures, submitted to Physics Letters
Novel Extrapolation Method in the Monte Carlo Shell Model
We propose an extrapolation method utilizing energy variance in the Monte
Carlo shell model in order to estimate the energy eigenvalue and observables
accurately. We derive a formula for the energy variance with deformed Slater
determinants, which enables us to calculate the energy variance efficiently.
The feasibility of the method is demonstrated for the full -shell
calculation of Ni, and the applicability of the method to a system
beyond current limit of exact diagonalization is shown for the
+-shell calculation of Ge.Comment: 4 pages, 4figure
Gaplessness of the Gaffnian
We study the Gaffnian trial wavefunction proposed to describe fractional
quantum Hall correlations at Bose filling factor and Fermi filling
. A family of Hamiltonians interpolating between a hard-core
interaction for which the physics is known and a projector whose ground state
is the Gaffnian is studied in detail. We give evidence for the absence of a gap
by using large-scale exact diagonalizations in the spherical geometry. This is
in agreement with recent arguments based on the fact that this wavefunction is
constructed from a non-unitary conformal field theory. By using the cylinder
geometry, we discuss in detail the nature of the underlying minimal model and
we show the appearance of heterotic conformal towers in the edge energy
spectrum where left and right movers are generated by distinct primary
operators.Comment: 11 pages, 5 figure
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