56 research outputs found
Low energy collective modes of deformed superfluid nuclei within the finite amplitude method
Background: The major challenge for nuclear theory is to describe and predict
global properties and collective modes of atomic nuclei. Of particular interest
is the response of the nucleus to a time-dependent external field that impacts
the low-energy multipole and beta-decay strength.
Purpose: We propose a method to compute low-lying collective modes in
deformed nuclei within the finite amplitude method (FAM) based on the
quasiparticle random-phase approximation (QRPA). By using the analytic property
of the response function, we find the QRPA amplitudes by computing the residua
of the FAM amplitudes by means of a contour integration around the QRPA poles
in a complex frequency plane.
Methods: We use the superfluid nuclear density functional theory with Skyrme
energy density functionals, FAM-QRPA approach, and the conventional matrix
formulation of the QRPA (MQRPA).
Results: We demonstrate that the complex-energy FAM-QRPA method reproduces
low-lying collective states obtained within the conventional matrix formulation
of the QRPA theory. Illustrative calculations are performed for the isoscalar
monopole strength in deformed 24Mg and for low-lying K = 0 quadrupole
vibrational modes of deformed Yb and Er isotopes.
Conclusions: The proposed FAM-QRPA approach allows one to efficiently
calculate low-lying collective modes in spherical and deformed nuclei
throughout the entire nuclear landscape, including shape-vibrational
excitations, pairing vibrational modes, and beta-decay rates.Comment: 9 pages, 2 figures, submitted to Phys. Rev.
Gauge-Invariant Formulation of Adiabatic Self-Consistent Collective Coordinate Method
The adiabatic self-consistent collective coordinate (ASCC) method is a
practical microscopic theory of large-amplitude collective motions in nuclei
with superfluidity. We show that its basic equations are invariant against
transformations involving the gauge angle in the particle-number space. By
virtue of this invariance, a clean separation between the large-amplitude
collective motion and the pairing rotational motion can be achieved, enabling
us to restore the particle-number symmetry broken by the
Hartree-Fock-Bogoliubov (HFB) approximation. We formulate the ASCC method
explicitly in a gauge-invariant form. In solving the ASCC equations, it is
necessary to fix the gauge. Applying this new formulation to the multi-O(4)
model, we compare different gauge-fixing procedures and demonstrate that
calculations using different gauges indeed yield the same results for
gauge-invariant quantities, such as the collective path and quantum spectra. We
suggest a gauge-fixing prescription that seems most convenient in realistic
calculations.Comment: 27 pages, 7 figures, submitted to Prog. Theor. Phy
Local alpha strength in the mean-field approximation
The local alpha strength is proposed to quantify the possibility to form an
alpha particle at a specific location inside the nucleus. It also provides the
strength of ground and excited states in the residual nuclei after the removal
of the alpha particle. We use the Hartree-Fock-plus-BCS (HF+BCS) method in the
calculation of the local alpha strengths for Sn isotopes. The local alpha
strengths are easily calculable and the results are consistent with recent
experimental data for Sn isotopes.Comment: 11 pages, 10 figure
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