Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session Y8: Novel Approaches in Nuclear Theory |
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Sponsoring Units: DNP Chair: James Vary, Iowa State University Room: Delaware B |
Tuesday, February 16, 2010 1:30PM - 1:42PM |
Y8.00001: Mitigating the sign problem for non-relativistic fermions on the lattice Andrei Kryjevski We study the fermion sign problem in a theory of non-relativistic fermions with a spin-independent repulsive interaction. We work in polar co-ordinates in momentum space, which makes it straightforward to keep only the low-energy degrees of freedom close to the Fermi surface. This is sufficient for the purpose of calculating many physically important low-energy observables. We find indications that the sign problem in the high-density effective theory will be weaker than in the full theory, so low-energy properties of the theory could be calculated by modifying the action to make it positive semi-definite and including reweighting factors in the observables. We discuss suitable modifications of the action, and describe a possible lattice realization of the polar momentum space formulation of the theory. [Preview Abstract] |
Tuesday, February 16, 2010 1:42PM - 1:54PM |
Y8.00002: Factorization of Operators Evolved with the Similarity Renormalization Group E.R. Anderson, S.K. Bogner, R.J. Furnstahl, R.J. Perry The Similarity Renormalization Group (SRG) flow equations are a series of unitary transformations which can be used to to achieve different patterns of decoupling in a Hamiltonian. An SRG transformation applied to internucleon interactions leads to greatly improved convergence properties.\footnote{S.K. Bogner, R.J. Furnstahl, and R.J. Perry, Phys. Rev. C 75 (2007) 061001.} A principal advantage of SRG transformations is that all operators can be consistently transformed, so that all observables are invariant. Calculations of the two-body momentum-distribution reveal an apparent factorization of the unitary transformation, \(U(k,q) \approx K(k)Q(q)\) for \(k\ll\lambda\) and \(q\gg\lambda\). The emergence of a nonrelativistic operator product expansion and factorization will be discussed. [Preview Abstract] |
Tuesday, February 16, 2010 1:54PM - 2:06PM |
Y8.00003: High-density behavior of nuclear symmetry energy Chang Xu, Bao-an Li One of the key issues in nuclear physics and astrophysics is to determine the density dependence of nuclear symmetry energy $E_{sym}(\rho)$. At sub-saturation densities, recent nuclear reaction experiments on isospin-sensitive observables of intermediate-energy have already provided us some constraints on the symmetry energy. However, at higher densities, there exists a large uncertainty in determining the stiffness or softness of the symmetry energy. We demonstrate the high-density behavior of nuclear symmetry energy within the framework of the Thomas-Fermi model. In a transparent way, the symmetry energy is decomposed into three parts: kinetic energy contribution, isoscalar potential contribution, and isovector potential contribution that arises from the difference of NN interactions in isospin singlet (T=0) and triplet (T=1) states. By incorporating the in- medium effect, it is found that the high-density behavior of symmetry energy is very sensitive to the competition between different spin-isospin channels. The circumstantial evidence of a rather soft symmetry energy at SIS/GSI is possibly due to the strong contribution of in-medium effect in the isospin singlet channel. [Preview Abstract] |
Tuesday, February 16, 2010 2:06PM - 2:18PM |
Y8.00004: Investigations of the perturbativeness of the particle-hole channel in nuclear matter Sunethra Ramanan, Richard Furnstahl, Scott Bogner Conventional nuclear many-body calculations are strongly non-perturbative in the inter-nucleon interactions. This non-perturbative behavior arises from several sources: 1. a strongly repulsive short-range interaction, 2. a tensor force, e.g. from pion exchange, which is highly singular at short-distances, 3. the presence of low-energy bound states or nearly bound states (in the S waves). The Renormalization Group based effective potentials exploit the insensitivity of the long-distance physics to the details of the short-distance physics. When these effective potentials are used in nuclear many-body calculations, it has been observed that these sources of non-perturbative behavior are density and/or resolution scale dependent. As a result, the bulk properties of nuclear matter turn out to be perturbative at least in the particle-particle channel. In this talk the question of ``perturbativeness'' of the particle-hole channel in nuclear matter is investigated by comparing the exact RPA correlation energy to a perturbative one. The cut-off and/or regulator dependence of these result give us an estimate of size of the missing many-body forces. [Preview Abstract] |
Tuesday, February 16, 2010 2:18PM - 2:30PM |
Y8.00005: Application of basis function light front quantization to QED - the electron anomalous magnetic moment Heli Honkanen, Jun Li, Pieter Maris, James Vary, Stan Brodsky, Avaroth Harindranath, Guy de Teramond Working with a basis function expansion for the fields, we quantize the light-front QED Hamiltonian, adopt the light-front gauge, introduce convenient regulators and solve the test problem of the anomalous magnetic moment of the electron. The calculation is non-perturbative and is compared with the Schwinger result in the perturbative limit to assess the numerical precision. Our choice for the orthonormal and complete set of basis functions consists of two-dimensional harmonic oscillator basis for the transverse modes, that corresponds with eigensolutions of the soft-wall AdS/QCD model obtained from light-front holography, and a discretized momentum space basis for the longitudinal modes. Working within the lepton and lepton-photon Fock space sectors, we analyze the divergences in our approach and adopt a sector-dependent remormalization scheme. [Preview Abstract] |
Tuesday, February 16, 2010 2:30PM - 2:42PM |
Y8.00006: Evolution of binary fragmentation saddle configurations with excitation energy Jan Toke The dependence of binary fragmentation saddle shapes and saddle energies on excitation energy was studied within the interacting Fermi gas liquid drop model. Two different parameterizations of saddle shapes were explored - such as described by Cassini ovals and by families of stitched surfaces of revolution of quadratic functions. It was found that independently of the type of parameterization and largely due to the effects of surface entropy, the saddle-state energies decrease with increasing excitation energy, while saddle shapes become more compact. The latter is consistent with recent experimental observations of an effective or apparent vanishing of Coulomb energy with increasing excitation, as parameterized in the Berkeley version of the Fisher's droplet model. The findings are directly useful for the updating of statistical compound nucleus decay codes in their handling of the intermediate-mass fragment emission. [Preview Abstract] |
Tuesday, February 16, 2010 2:42PM - 2:54PM |
Y8.00007: Transport Properties in Cold Dense Quark Matter Matt Braby, Thomas Schaefer, Jingyi Chao, Mark Alford, Simin Mahmoodifar We have calculated several transport properties of the low energy degrees of freedom of the color-flavor locked phase in dense quark matter. The low energy degrees of freedom are the superfluid phonon and the meson octet of which the lightest excitation is the kaon. In some choices of the parameters, the kaon can condense. The basis of the calculation is a matching of kinetic theory and hydrodynamics to extract the transport properties and calculating the appropriate scattering rates for each process. From this, we have calculated the bulk viscosity of condensed and massive kaons, the shear viscosity of condensed kaons, and the thermal conductivity of the superfluid phonons and massive kaons. We present the results and analyze how these transport properties could affect observables in compact stars. [Preview Abstract] |
Tuesday, February 16, 2010 2:54PM - 3:06PM |
Y8.00008: Perturbation theory for isotropic velocity-dependent potentials: scattering case Mahmoud Jaghoub The time-independent Schr\"{o}dinger equation with an isotropic velocity-depen\-dent potential is considered. Treating the velocity-dependent interaction as a small perturbation we develop analytical formulae for the changes in the scattering phase shifts and wave functions. It is shown that only the zeroth order solution and the perturbing potential are needed to determine the phase shift and wave function corrections. No prior knowledge of the unperturbed scattering states continuum is required. In order to test the validity of our approach we applied it to an exactly solvable model for nucleon-nucleon scattering. The results of the perturbation formalism compare quite well with the those of the exactly solvable model. The developed formalism can be applied in problems concerning pion-nucleon, nucleon-nucleon and electron-atom scattering. It may also be useful in studying the scattering of electrons in semiconductor heterostructures. [Preview Abstract] |
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