5 research outputs found
Effects of isospin mixing in the A=32 quintet
For the A=32 T=2 quintet we provide a unified theoretical description for
three related aspects of isospin mixing: the necessity of more than three terms
in the isobaric mass multiplet equation, isospin-forbidden proton decay, and a
correction to the allowed Fermi beta decay. We demonstrate for the first time
that all three effects observed in experiment can be traced to a common origin
related to isospin mixing of the T=2 states with T=1 states
Renormalized interactions with a realistic single particle basis
Neutron-rich isotopes in the sdpf space with Z < 15 require modifications to
derived effective interactions to agree with experimental data away from
stability. A quantitative justification is given for these modifications due to
the weakly bound nature of model space orbits via a procedure using realistic
radial wavefunctions and realistic NN interactions. The long tail of the radial
wavefunction for loosely bound single particle orbits causes a reduction in the
size of matrix elements involving those orbits, most notably for pairing matrix
elements, resulting in a more condensed level spacing in shell model
calculations. Example calculations are shown for 36Si and 38Si.Comment: 6 page
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
Quasiparticle Coupled Cluster Theory for Pairing Interactions
We present an extension of the pair coupled cluster doubles (p-CCD) method to
quasiparticles and apply it to the attractive pairing Hamiltonian. Near the
transition point where number symmetry gets spontaneously broken, the proposed
BCS-based p-CCD method yields significantly better energies than existing
methods when compared to exact results obtained via solution of the Richardson
equations. The quasiparticle p-CCD method has a low computational cost of
as a function of system size. This together with the high
quality of results here demonstrated, points to considerable promise for the
accurate description of strongly correlated systems with more realistic pairing
interactions