751 research outputs found
Unified ab initio approaches to nuclear structure and reactions
The description of nuclei starting from the constituent nucleons and the
realistic interactions among them has been a long-standing goal in nuclear
physics. In addition to the complex nature of the nuclear forces, with two-,
three- and possibly higher many-nucleon components, one faces the
quantum-mechanical many-nucleon problem governed by an interplay between bound
and continuum states. In recent years, significant progress has been made in ab
initio nuclear structure and reaction calculations based on input from
QCD-employing Hamiltonians constructed within chiral effective field theory.
After a brief overview of the field, we focus on ab initio many-body approaches
- built upon the No-Core Shell Model - that are capable of simultaneously
describing both bound and scattering nuclear states, and present results for
resonances in light nuclei, reactions important for astrophysics and fusion
research. In particular, we review recent calculations of resonances in the
He halo nucleus, of five- and six-nucleon scattering, and an investigation
of the role of chiral three-nucleon interactions in the structure of Be.
Further, we discuss applications to the BeB radiative
capture. Finally, we highlight our efforts to describe transfer reactions
including the HHe fusion.Comment: Contribution to the Special Physica Scripta Edition - 40 year
anniversary - Nobel Prize '75, 71 pages, 29 figure
Accelerating many-nucleon basis generation for high performance computing enabled ab initio nuclear structure studies
We present the problem of generating a many-nucleon basis in SU(3) -scheme for ab initio nuclear structure calculations in a symmetry-adapted no-core shell model framework. We first discuss and analyze the basis construction algorithm whose baseline implementation quickly becomes a significant bottleneck for large model spaces and heavier nuclei. The outcomes of this analysis are utilized to propose a new scalable version of the algorithm. Its performance is consequently studied empirically using the Blue Waters supercomputer. The measurements show significant acceleration achieved with over two orders of magnitude speedups realized for larger model spaces
Large-scale exact diagonalizations reveal low-momentum scales of nuclei
Ab initio methods aim to solve the nuclear many-body problem with controlled
approximations. Virtually exact numerical solutions for realistic interactions
can only be obtained for certain special cases such as few-nucleon systems.
Here we extend the reach of exact diagonalization methods to handle model
spaces with dimension exceeding on a single compute node. This allows
us to perform no-core shell model (NCSM) calculations for 6Li in model spaces
up to and to reveal the 4He+d halo structure of this
nucleus. Still, the use of a finite harmonic-oscillator basis implies
truncations in both infrared (IR) and ultraviolet (UV) length scales. These
truncations impose finite-size corrections on observables computed in this
basis. We perform IR extrapolations of energies and radii computed in the NCSM
and with the coupled-cluster method at several fixed UV cutoffs. It is shown
that this strategy enables information gain also from data that is not fully UV
converged. IR extrapolations improve the accuracy of relevant bound-state
observables for a range of UV cutoffs, thus making them profitable tools. We
relate the momentum scale that governs the exponential IR convergence to the
threshold energy for the first open decay channel. Using large-scale NCSM
calculations we numerically verify this small-momentum scale of finite nuclei.Comment: Minor revisions.Accepted for publication in Physical Review
Perspectives of Nuclear Physics in Europe: NuPECC Long Range Plan 2010
The goal of this European Science Foundation Forward Look into the future of Nuclear Physics is to bring together
the entire Nuclear Physics community in Europe to formulate a coherent plan of the best way to develop the field in
the coming decade and beyond.<p></p>
The primary aim of Nuclear Physics is to understand the origin, evolution, structure and phases of strongly interacting matter, which constitutes nearly 100% of the visible matter in the universe. This is an immensely important and challenging task that requires the concerted effort of scientists working in both theory and experiment, funding agencies, politicians and the public.<p></p>
Nuclear Physics projects are often “big science”, which implies large investments and long lead times. They need careful forward planning and strong support from policy makers. This Forward Look provides an excellent tool to achieve this. It represents the outcome of detailed scrutiny by Europe’s leading experts and will help focus the views of the scientific community on the most promising directions in the field and create the basis for funding agencies to provide adequate support.<p></p>
The current NuPECC Long Range Plan 2010 “Perspectives of Nuclear Physics in Europe” resulted from consultation
with close to 6 000 scientists and engineers over a period of approximately one year. Its detailed recommendations
are presented on the following pages. For the interested public, a short summary brochure has been produced to
accompany the Forward Look.<p></p>
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