Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session BE: Nuclear Theory: Computational |
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Chair: Calvin Johnson, San Diego State University Room: Simmons Ballroom 1 |
Friday, October 24, 2008 8:30AM - 8:42AM |
BE.00001: Ab initio many-body calculations of nucleon scattering on $^{16}$O Petr Navratil, Sofia Quaglioni, Robert Roth We develop a new {\it ab initio} many-body approach\footnote{S. Quaglioni and P. Navratil, arXiv:0804.1560.} capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method\footnote{Y. C. Tang {\it et al.}, Phys. Rep. {\bf 47}, 167 (1978); K. Langanke and H. Friedrich, Advances in Nuclear Physics, Plenum, New York, 1987.} with the {\it ab initio} no-core shell model (NCSM).\footnote{P. Navratil, J. P. Vary, and B. R. Barrett, Phys. Rev. Lett. {\bf 84}, 5728 (2000); Phys. Rev. C {\bf 62}, 054311 (2000).} In this way, we complement a microscopic-cluster technique with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters, while preserving Pauli principle and translational symmetry. We will present results for low-energy nucleon scattering on $^{16}$O and for $A=17$ bound states obtained using realistic nucleon-nucleon potentials. The $^{16}$O wave functions are calculated within the importance-truncated NCSM\footnote{R. Roth and P. Navratil, Phys. Rev. Lett. {\bf 99}, 092501 (2007).} that allows the use of model spaces up to $\approx 18\hbar\Omega$ and ultimately enables to reach convergence of phase-shifts and other observables. Prepared by LLNL under Contract DE-AC52-07NA27344. Support from the U.S. DOE/SC/NP (Work Proposal No. SCW0498), and from the U. S. Department of Energy Grant DE-FC02-07ER41457 is acknowledged. [Preview Abstract] |
Friday, October 24, 2008 8:42AM - 8:54AM |
BE.00002: Time-dependent Green's Functions Approach to Nuclear Reactions Arnau Rios Huguet, Pawel Danielewicz, Brent Barker Nonequilibrium Green's functions represent underutilized means of studying the time evolution of quantum many-body systems. The Kadanoff-Baym equations describe the time evolution of quantum systems including memory effects and correlations beyond the mean field [1]. In nuclear physics, these have been solved for homogeneous matter [2,3], but few is known about the effects that correlations induce in a dynamical description of finite nuclei. This is particularly relevant for the case of central low-energy reactions (fusion, fission), where dissipative effects come into play [4]. We discuss the mean-field evolution for the density matrix of colliding slabs in 1D [5] and describe the extension of the dynamics to the correlated case in the Born approximation. \newline [1] G. Baym, Phys. Rev. 127, 1391 (1962). \newline [2] P. Danielewicz, Ann. Phys. 152, 305 (1984). \newline [3] H. S. K\"ohler, Phys. Rev. C 51, 3232 (1995). \newline [4] M. Tohyama and A. S. Umar, Phys. Rev. C 65, 037601 (2002). \newline [5] A. Rios and P. Danielewicz, arxiv:0801.4171. [Preview Abstract] |
Friday, October 24, 2008 8:54AM - 9:06AM |
BE.00003: ABSTRACT WITHDRAWN |
Friday, October 24, 2008 9:06AM - 9:18AM |
BE.00004: S-wave Pairing In Neutron Matter Alexandros Gezerlis, Joseph Carlson Low-density neutron matter is a strongly paired system, with a pairing gap of the order of the Fermi energy. Several many-body schemes have been devised in an attempt to calculate this pairing gap, since an accurate calculation of neutron matter properties may be important to the physics of neutron stars and of neutron-rich nuclei. We have calculated the T=0 equation of state and pairing gap for low-density neutron matter (as a function of the Fermi momentum times the scattering length) using a Quantum Monte Carlo method. These results are compared with previous calculations, including a recent work that makes use of the Auxiliary Field Diffusion Monte Carlo method, and also with infinitesimal-range calculations relevant to cold-atom physics. [Preview Abstract] |
Friday, October 24, 2008 9:18AM - 9:30AM |
BE.00005: Generalized Auxiliary Field Monte Carlo method: a new efficient variational method for CBF theory Mohamed Bouadani A principle goal in nuclear theory is the development of computational methods to calculate hadronic systems properties. Correlated basis function theory, CBF, is believed to offer an accurate wave-function. Two approaches that have made important contributions are the diagrammatic viewpoint that try to compute in a self consistent way to all orders the dominant leading order diagrams such as the Fermi hypernetted Chain/ Single Operator Chain and Coupled Cluster theory, and, on the other hand, there are methods like Green function Monte Carlo, that aim to compute expectations of observables by stochastically evaluating the integrals via Monte Carlo method. Each of these approaches suffer important limitations that make further advances very difficult. To circumvent the principle obstacle, being that these correlations are state dependent and thus making any evaluation of such complex wave-function impractical for large systems, a new method designated as the Generalized Auxiliary Fields Variational Monte Carlo, GAFVMC method has been successively implemented for the stochastic sampling of the CBF-type wave-functions with $v_6$ type operators. Some encouraging results will be given. [Preview Abstract] |
Friday, October 24, 2008 9:30AM - 9:42AM |
BE.00006: A Random Matrix Study of the QCD Sign Problem Jilong Han, Mikhail Stephanov We investigate the severity of the sign problem in a random matrix model for QCD at finite temperature T and baryon chemical potential mu. We obtain analytic expression for the average phase factor -- the measure of the severity of the sign problem at arbitrary T and mu. We observe that the sign problem becomes less severe as the temperature is increased. We also find the domain where the sign problem is maximal -- the average phase factor is zero, which is related to the pion condensation phase in the QCD with finite isospin chemical potential. We find that, in the matrix model we studied, the critical point is located inside the domain of the maximal sign problem, making the point inaccessible to conventional reweighting techniques. We observe and describe the scaling behavior of the size and shape of the pion condensation near the chiral limit. [Preview Abstract] |
Friday, October 24, 2008 9:42AM - 9:54AM |
BE.00007: Current status of our microscopic predictions of the equation of state Francesca Sammarruca Intense experimental efforts to constraint the nuclear equation of state (EoS) are in progress or in the planning stage. Isospin asymmetry is of particular interest. Therefore, corresponding theoretical calculations are important and timely. We will present and discuss most recent progress in our systematic exploring of diverse aspects of the equation of state, which includes predictions of hyperon energies in nuclear matter. Consideration of strangeness in the EoS is important in the low to normal density regime, where it complements studies of hypernuclei, as well as at the high densities typical for the core of neutron stars. [Preview Abstract] |
Friday, October 24, 2008 9:54AM - 10:06AM |
BE.00008: Correlated momentum distribution in asymmetric nuclear matter Arnau Rios Huguet The understanding of the variation of microscopic nuclear properties with isospin asymmetry is an important issude for both nuclear experiments and theory. The recent results on nucleon knock-out reactions seem to indicate that there is a strong dependence of spectroscopic factor on isospin [1]. This could indicate that the occupation numbers of low-lying nuclear states are changing with asymmetry [2]. We perform realistic many-body calculations of asymmetric nuclear matter within the Self-Consistent Green's Functions method to study the impact of isospin asymmetry on the correlated momentum distributions of asymmetric nuclear matter [2,3]. Using different internucleon potentials, we assess the model dependence of these calculations and conclude that the change of $n(k)$ with isospin is well constrained from realistic calculations. \newline [1] A. Gade et al., Phys. Rev. C 77, 044306 (2008). \newline [2] T. Frick et al., Phys. Rev. C 71, 014313 (2005). \newline [3] W. Dickhoff and C. Barbieri, Prog. Part. Nucl. Phys 52, 377 (2004). [Preview Abstract] |
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