1,637 research outputs found
Similarity Renormalization Group for Few-Body Systems
Internucleon interactions evolved via flow equations yield soft potentials
that lead to rapid variational convergence in few-body systems.Comment: 3 pages, 6 figures. To appear in the proceedings of the 20th European
Conference on Few-Body Problems in Physics (EFB20), Pisa, September 10-14,
200
Density Matrix Expansion for Low-Momentum Interactions
A first step toward a universal nuclear energy density functional based on
low-momentum interactions is taken using the density matrix expansion (DME) of
Negele and Vautherin. The DME is adapted for non-local momentum-space
potentials and generalized to include local three-body interactions. Different
prescriptions for the three-body DME are compared. Exploratory results are
given at the Hartree-Fock level, along with a roadmap for systematic
improvements within an effective action framework for Kohn-Sham density
functional theory.Comment: 50 pages, 10 figure
From low-momentum interactions to nuclear structure
We present an overview of low-momentum two-nucleon and many-body interactions
and their use in calculations of nuclei and infinite matter. The softening of
phenomenological and effective field theory (EFT) potentials by renormalization
group (RG) transformations that decouple low and high momenta leads to greatly
enhanced convergence in few- and many-body systems while maintaining a
decreasing hierarchy of many-body forces. This review surveys the RG-based
technology and results, discusses the connections to chiral EFT, and clarifies
various misconceptions.Comment: 76 pages, 57 figures, two figures updated, published versio
Are low-energy nuclear observables sensitive to high-energy phase shifts?
Conventional nucleon-nucleon potentials with strong short-range repulsion
require contributions from high-momentum wave function components even for
low-energy observables such as the deuteron binding energy. This can lead to
the misconception that reproducing high-energy phase shifts is important for
such observables. Interactions derived via the similarity renormalization group
decouple high-energy and low-energy physics while preserving the phase shifts
from the starting potential. They are used to show that high-momentum
components (and high-energy phase shifts) can be set to zero when using
low-momentum interactions, without losing information relevant for low-energy
observables.Comment: 13 pages, 5 figures; reference and acknowledgment adde
Operator Evolution via the Similarity Renormalization Group I: The Deuteron
Similarity Renormalization Group (SRG) flow equations can be used to
unitarily soften nuclear Hamiltonians by decoupling high-energy intermediate
state contributions to low-energy observables while maintaining the natural
hierarchy of many-body forces. Analogous flow equations can be used to
consistently evolve operators so that observables are unchanged if no
approximations are made. The question in practice is whether the advantages of
a softer Hamiltonian and less correlated wave functions might be offset by
complications in approximating and applying other operators. Here we examine
the properties of SRG-evolved operators, focusing in this paper on applications
to the deuteron but leading toward methods for few-body systems. We find the
advantageous features generally carry over to other operators with additional
simplifications in some cases from factorization of the unitary transformation
operator.Comment: 33 pages, 19 figures. Improved figures 17 and 18. Expanded comments
on OPE in tex
Computer Tomograph Measurements in Shear and Gravity Particle Flows
The paper reports the recent results obtained on the applicability of cross-sectional digital
imaging method to study particle flow characteristics in 3D particle beds forced to move by
gravity or shear. X-ray CT imaging technique is widely used in medical diagnostics and, during
the last decades, its spatial and temporal resolution has been improved significantly. In this study,
an attempt was made to use this technique for engineering purposes. Two experimental set-ups
with different types of particle flows were investigated using Siemens Somatom Plus type CT
equipment. A series of trials were carried out in a small model hopper with flat bottom and
almost cylindrical side wall slightly deviating from verticality. Non steady-state flow was studied
during the outflow of particulate material from this vessel, through a central hole at the bottom.
Further investigation was fulfilled in a modified Cuette-type shearing device to study steady-state
shear flow. This equipment consisted of an almost cylindrical vessel identical to that used for
gravity flow measurements, and a smaller inner cylinder rotating within this vessel concentrically,
around its vertical axis. The surface of the inner cylinder was notched vertically, i.e.
perpendicularly to the direction of rotation to increase wall friction between the particles and the
cylinder. Almost spherical sucrose granules, also used for gravity flow measurements, were filled
into the gap between the rotating cylinder and the outer wall of the equipment. Movement of
particles took place due to shear, generated within the particle bed. By using X-ray CT technique,
cross-sectional digital images were obtained in every two seconds for both types of particle flows.
For this, the cross-sectional variation of the local Hounsfield density values were measured in a
matrix of 0.1x0.1x2.0 mm space elements. It was proved that the applied non-invasive crosssectional
imaging technique was suitable to distinguish the stationary and moving particle
regions, and by this, to estimate the location of the boundary zone between them
Operator Evolution via the Similarity Renormalization Group I: The Deuteron
Similarity Renormalization Group (SRG) flow equations can be used to
unitarily soften nuclear Hamiltonians by decoupling high-energy intermediate
state contributions to low-energy observables while maintaining the natural
hierarchy of many-body forces. Analogous flow equations can be used to
consistently evolve operators so that observables are unchanged if no
approximations are made. The question in practice is whether the advantages of
a softer Hamiltonian and less correlated wave functions might be offset by
complications in approximating and applying other operators. Here we examine
the properties of SRG-evolved operators, focusing in this paper on applications
to the deuteron but leading toward methods for few-body systems. We find the
advantageous features generally carry over to other operators with additional
simplifications in some cases from factorization of the unitary transformation
operator.Comment: 33 pages, 19 figures. Improved figures 17 and 18. Expanded comments
on OPE in tex
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