46,289 research outputs found
Ab initio approach to s-shell hypernuclei 3H_Lambda, 4H_Lambda, 4He_Lambda and 5He_Lambda with a Lambda N-Sigma N interaction
Variational calculations for s-shell hypernuclei are performed by explicitly
including degrees of freedom. Four sets of YN interactions (SC97d(S),
SC97e(S), SC97f(S) and SC89(S)) are used. The bound-state solution of
He is obtained and a large energy expectation value of the tensor
transition part is found. The internal energy of the
He subsystem is strongly affected by the presence of a particle
with the strong tensor transition potential.Comment: Phys. Rev. Lett. 89, 142504 (2002
Ab initio study of the photoabsorption of He
There are some discrepancies in the low energy data on the photoabsorption
cross section of He. We calculate the cross section with realistic nuclear
forces and explicitly correlated Gaussian functions. Final state interactions
and two- and three-body decay channels are taken into account. The cross
section is evaluated in two methods: With the complex scaling method the total
absorption cross section is obtained up to the rest energy of a pion, and with
the microscopic -matrix method both cross sections He()H
and He()He are calculated below 40\,MeV. Both methods give
virtually the same result. The cross section rises sharply from the H+
threshold, reaching a giant resonance peak at 26--27\,MeV. Our calculation
reproduces almost all the data above 30\,MeV. We stress the importance of
H+ and He+ cluster configurations on the cross section as well as
the effect of the one-pion exchange potential on the photonuclear sum rule.Comment: 15 pages, 12 figure
Coulomb corrected eikonal description of the breakup of halo nuclei
The eikonal description of breakup reactions diverges because of the Coulomb
interaction between the projectile and the target. This divergence is due to
the adiabatic, or sudden, approximation usually made, which is incompatible
with the infinite range of the Coulomb interaction. A correction for this
divergence is analysed by comparison with the Dynamical Eikonal Approximation,
which is derived without the adiabatic approximation. The correction consists
in replacing the first-order term of the eikonal Coulomb phase by the
first-order of the perturbation theory. This allows taking into account both
nuclear and Coulomb interactions on the same footing within the computationally
efficient eikonal model. Excellent results are found for the dissociation of
11Be on lead at 69 MeV/nucleon. This Coulomb Corrected Eikonal approximation
provides a competitive alternative to more elaborate reaction models for
investigating breakup of three-body projectiles at intermediate and high
energies.Comment: 19 pages, 9 figures, accepted for publication in Phys. Rev.
Spin Fluid Dynamics Observed by Magnetic Fountain Effect and Mechano-Spin Effect in the Ferromagnetic Superfluid He A Phase
Systematic observations of the magnetically generated fountain pressure in
the superfluid He A have been carried out in a newly built apparatus
designed to reduce the effect of thermal gradients. In the same apparatus,
mechanical pumping and filtering of polarized nuclear spins were realized by
the pneumatic pumping action of an electrostatically actuated membrane. In both
experiments, the measured induced pressure was observed to decay at all
temperatures where the A phase appeared in magnetic fields up to 13 T and
liquid pressures between 1 and 29 bar. The inferred spin relaxation rate tended
to increase as the low temperature phase boundary with the A phase
(T) was approached. The increase in spin relaxation rate near T
can be explained by the presence of a minority spin condensate in the A
phase as predicted by Monien and Tewordt and by the application of the
Leggett-Takagi theory of spin relaxation in superfluid He.Comment: 12 pages, 15 figures, to appear in Physical Review
Effective single-band models for strongly interacting fermions in an optical lattice
To test effective Hamiltonians for strongly interacting fermions in an
optical lattice, we numerically find the energy spectrum for two fermions
interacting across a Feshbach resonance in a double well potential. From the
spectrum, we determine the range of detunings for which the system can be
described by an effective lattice model, and how the model parameters are
related to the experimental parameters. We find that for a range of strong
interactions the system is well described by an effective model, and the
effective superexchange term, , can be smoothly tuned through zero on either
side of unitarity. Right at and around unitarity, an effective one-band general
Hubbard model is appropriate, with a finite and small on-site energy, due to a
lattice-induced anharmonic coupling between atoms at the scattering threshold
and a weakly bound Feshbach molecule in an excited center of mass state.Comment: 7 pages, 7 figures; minor typos correcte
Extrapolation Method for the No-Core Shell Model
Nuclear many-body calculations are computationally demanding. An estimate of
their accuracy is often hampered by the limited amount of computational
resources even on present-day supercomputers. We provide an extrapolation
method based on perturbation theory, so that the binding energy of a large
basis-space calculation can be estimated without diagonalizing the Hamiltonian
in this space. The extrapolation method is tested for 3H and 6Li nuclei. It
will extend our computational abilities significantly and allow for reliable
error estimates.Comment: 8 pages, 7 figures, PRC accepte
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