24,162 research outputs found
The Unitary Correlation Operator Method from a Similarity Renormalization Group Perspective
We investigate how the Unitary Correlation Operator Method (UCOM), developed
to explicitly describe the strong short-range central and tensor correlations
present in the nuclear many-body system, relates to the Similarity
Renormalization Group (SRG), a method to band-diagonalize Hamiltonians by
continuous unitary transformations. We demonstrate how the structure of the
UCOM transformation, originally motivated from the physically intuitive picture
of correlations in coordinate space, arises naturally from the SRG flow
equation. Apart from formal considerations we show that the momentum space
matrix elements of the effective interactions obtained in both schemes agree
extremely well.Comment: 5 pages, 2 figures, using REVTEX4; v2: references adde
Mean-field instability of trapped dilute boson-fermion mixtures
The influence of boson-boson and boson-fermion interactions on the stability
of a binary mixture of bosonic and fermionic atoms is investigated. The density
profiles of the trapped mixture are obtained from direct numerical solution of
a modified Gross-Pitaevskii equation that is self-consistently coupled to the
mean-field generated by the interaction with the fermionic species. The
fermions which in turn feel the mean-field created by the bosons are treated in
Thomas-Fermi approximation. We study the effects of different combinations of
signs of the boson-boson and the boson-fermion scattering lengths and determine
explicit expressions for critical particle numbers as function of these
scattering lengths.Comment: 4 pages, 2 figures (using RevTeX4
Quasiparticle Random Phase Approximation with Interactions from the Similarity Renormalization Group
We have developed a fully consistent framework for calculations in the
Quasiparticle Random Phase Approximation (QRPA) with interactions from the
Similarity Renormalization Group (SRG) and other unitary transformations of
realistic interactions. The consistency of our calculations, which use the same
Hamiltonian to determine the Hartree-Fock-Bogoliubov (HFB) ground states and
the residual interaction for QRPA, guarantees an excellent decoupling of
spurious strength, without the need for empirical corrections. While work is
under way to include SRG-evolved 3N interactions, we presently account for some
3N effects by means of a linearly density-dependent interaction, whose strength
is adjusted to reproduce the charge radii of closed-shell nuclei across the
whole nuclear chart. As a first application, we perform a survey of the
monopole, dipole, and quadrupole response of the calcium isotopic chain and of
the underlying single-particle spectra, focusing on how their properties depend
on the SRG parameter . Unrealistic spin-orbit splittings suggest that
spin-orbit terms from the 3N interaction are called for. Nevertheless, our
general findings are comparable to results from phenomenological QRPA
calculations using Skyrme or Gogny energy density functionals. Potentially
interesting phenomena related to low-lying strength warrant more systematic
investigations in the future.Comment: 18 pages, 17 figures, 3 tables (RevTeX 4.1), v2: fixed typos &
figures, as publishe
Density functional theory for hard-sphere mixtures: the White-Bear version Mark II
In the spirit of the White-Bear version of fundamental measure theory we
derive a new density functional for hard-sphere mixtures which is based on a
recent mixture extension of the Carnahan-Starling equation of state. In
addition to the capability to predict inhomogeneous density distributions very
accurately, like the original White-Bear version, the new functional improves
upon consistency with an exact scaled-particle theory relation in the case of
the pure fluid. We examine consistency in detail within the context of
morphological thermodynamics. Interestingly, for the pure fluid the degree of
consistency of the new version is not only higher than for the original
White-Bear version but also higher than for Rosenfeld's original fundamental
measure theory.Comment: 16 pages, 3 figures; minor changes; J. Phys.: Condens. Matter,
accepte
Nuclear Structure in the UCOM Framework: From Realistic Interactions to Collective Excitations
The Unitary Correlation Operator Method (UCOM) provides a means for nuclear
structure calculations starting from realistic NN potentials. The dominant
short-range central and tensor correlations are described explicitly by a
unitary transformation. The application of UCOM in the context of the no-core
shell model provides insight into the interplay between dominant short-range
and residual long-range correlations in the nuclear many-body problem. The use
of the correlated interaction within Hartree-Fock, many-body perturbation
theory, and Random Phase Approximation gives access to various nuclear
structure observables throughout the nuclear chart.Comment: 9 pages, 3 figures, invited talk at the 2nd Int. Conf. on "Collective
Motion in Nuclei under Extreme Conditions" (COMEX 2), Sankt Goar, German
Nuclear Structure and Response based on Correlated Realistic NN Interactions
Starting from the Argonne V18 nucleon-nucleon (NN) interaction and using the
Unitary Correlation Operator Method, a correlated interaction v_UCOM has been
constructed, which is suitable for calculations within restricted Hilbert
spaces. In this work we employ the v_UCOM in Hartree-Fock, perturbation-theory
and RPA calculations and we study the ground-state properties of various
closed-shell nuclei, as well as some excited states. The present calculations
provide also important feedback for the optimization of the v_UCOM and valuable
information on its properties. The above scheme offers the prospect of ab
initio calculations in nuclei, regardless of their mass number. It can be used
in conjunction with other realistic NN interactions as well, and with various
many-body methods (Second RPA, QRPA, Shell Model, etc.).Comment: 3 pages, incl. 2 figures; Proc. Int. Conf. on Frontiers in Nuclear
Structure, Astrophysics and Reactions (FINUSTAR), Kos, Greece, Sept.200
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