112 research outputs found
Computational aspects of nuclear coupled-cluster theory
We discuss computational aspects of the spherical coupled-cluster method
specific to the nuclear many-body problem. Using chiral nucleon-nucleon
interaction at next-to-next-to-next-to leading order (N3LO) with cutoff Lambda
= 500MeV, we present coupled-cluster results for the ground state of 40Ca.
Scaling and performance studies are presented together with challenges we meet
with when extending the coupled-cluster effort to nuclei mass hundred and
beyond.Comment: 9 pages, 5 figures, Proceedings for YKIS2011 Symposiu
Ab initio Bogoliubov coupled cluster theory for open-shell nuclei
Ab initio many-body methods address closed-shell nuclei up to mass A ~ 130 on
the basis of realistic two- and three-nucleon interactions. Several routes to
address open-shell nuclei are currently under investigation, including ideas
which exploit spontaneous symmetry breaking. Singly open-shell nuclei can be
efficiently described via the sole breaking of gauge symmetry associated
with particle number conservation, to account for their superfluid character.
The present work formulates and applies Bogoliubov coupled cluster (BCC)
theory, which consists of representing the exact ground-state wavefunction of
the system as the exponential of a quasiparticle excitation cluster operator
acting on a Bogoliubov reference state. Equations for the ground-state energy
and cluster amplitudes are derived at the singles and doubles level (BCCSD)
both algebraically and diagrammatically. The formalism includes three-nucleon
forces at the normal-ordered two-body level. The first BCC code is implemented
in -scheme, which will eventually permit the treatment of doubly open-shell
nuclei. Proof-of-principle calculations in an spherical
harmonic oscillator basis are performed for O, Ne,
Mg in the BCCD approximation with a chiral two-nucleon interaction,
comparing to results obtained in standard coupled cluster theory when
applicable. The breaking of symmetry is monitored by computing the
variance associated with the particle-number operator. The newly developed
many-body formalism increases the potential span of ab initio calculations
based on single-reference coupled cluster techniques tremendously, i.e.
potentially to reach several hundred additional mid-mass nuclei. The new
formalism offers a wealth of potential applications and further extensions
dedicated to the description of ground and excited states of open-shell nuclei.Comment: 22 pages, 13 figure
Irreversible Investments, Dynamic Inconsistency and Policy Convergence
We study a model where two parties, one from the left and one from the right, compete for position. The election is to be held in the near future and the outcome is uncertain. Prior to the election, the members of both parties nominate their prime ministerial candidates. Investors care about the outcome since they may invest in irreversible domestic production capital. We find that there is political convergence in the nomination process. In some circumstances, it is only the median voter of the left-wing party that elects a more moderate candidate. In other instances, the members of both parties nominate more “conservative” candidates, but there is still convergence. We also show that a higher probability of the left winning the election increases the degree of convergence, while a more globalised economy (greater capital mobility) reduces it.capital mobility, dynamic inconsistency, political competition, policy convergence
Irreversible investments, dynamic inconsistency and policy convergence
We study a model where two parties, one from the left and one from the right, compete for position. The election is to be held in the near future and the outcome is uncertain. Prior to the election, the members of both parties nominate their prime ministerial candidates. Investors care about the outcome since they may invest in irreversible domestic production capital. We find that there is political convergence in the nomination process. In some circumstances, it is only the median voter of the left-wing party that elects a more moderate candidate. In other instances, the members of both parties nominate more "conservative" candidates, but there is still convergence. We also show that a higher probability of the left winning the election increases the degree of convergence, while a more globalised economy (greater capital mobility) reduces it.Policy Objectives; Policy Designs and Consistency; Policy Coordination; International Investment; Long-Term Capital Movements; Personal Income and Other Nonbusiness Taxes and Subsidies; Political Economy.
Electric dipole polarizability: from few- to many-body systems
We review the Lorentz integral transform coupled-cluster method for the
calculation of the electric dipole polarizability. We benchmark our results
with exact hyperspherical harmonics calculations for 4He and then we move to a
heavier nucleus studying 16O. We observe that the implemented chiral
nucleon-nucleon interaction at next-to-next-to-next-to-leading order
underestimates the electric dipole polarizability.Comment: 4 pages, 2 figures, proceedings of the 21st International Conference
on Few-Body Problems in Physics (FB21), May 2015, Chicag
Effective Interaction Techniques for the Gamow Shell Model
We apply a contour deformation technique in momentum space to the newly
developed Gamow shell model, and study the drip-line nuclei 5He, 6He and 7He. A
major problem in Gamow shell-model studies of nuclear many-body systems is the
increasing dimensionality of many-body configurations due to the large number
of resonant and complex continuum states necessary to reproduce bound and
resonant state energies. We address this problem using two different effective
operator approaches generalized to the complex momentum plane. These are the
Lee-Suzuki similarity transformation method for complex interactions and the
multi-reference perturbation theory method. The combination of these two
approaches results in a large truncation of the relevant configurations
compared with direct diagonalization. This offers interesting perspectives for
studies of weakly bound systems.Comment: 18 pages, 17 figs, Revtex
- …