Bulletin of the American Physical Society
2016 Fall Meeting of the APS Division of Nuclear Physics
Volume 61, Number 13
Thursday–Sunday, October 13–16, 2016; Vancouver, BC, Canada
Session PG: Nuclear Theory |
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Sponsoring Units: DNP Chair: Calvin Johnson, San Diego State University Room: Pavilion Ballroom B |
Sunday, October 16, 2016 10:30AM - 10:42AM |
PG.00001: Dipole strength from first principles calculations Mirko Miorelli, Sonia Bacca, Nir Barnea, Gaute Hagen, Gustav R. Jansen, Thomas Papenbrock, Giuseppina Orlandini The electric dipole polarizability quantifies the low-energy behavior of the dipole strength. It is related to the proton and neutron distributions of the nucleus, and thereby can be used to constrain the neutron equation of state and the physics of neutron stars. Only recently however, new developments in $ab\ initio$ methods finally allowed first principles studies of the dipole strength in medium-mass nuclei [1,2]. Using the Lorentz integral transform coupled cluster method with the newly developed chiral interaction NNLO$_\rm{sat}$ we study the low energy behavior of the dipole strength in $^4$He, $^{16}$O and $^{22}$O [2]. For the exotic $^{22}$O we observe large contributions to the dipole strength at very low energy, indicating the presence of a pygmy dipole resonance, in agreement with what experimentally found by Leistenschneider $et\ al.$ [3]. We then study correlations between the electric dipole polarizability and the charge radius in $^{16}$O and $^{40}$Ca using a variety of realistic Hamiltonians, showing the importance of three-nucleon forces [2]. [1] S. Bacca $et\ al.$, Phys. Rev. C 90, 064619 (2014) [2] M. Miorelli $et\ al.$, arXiv:1604.05381 (2016) [3] A. Leistenschneider $et\ al.$, Phys. Rev. Lett. 86, 5442-5445 (2001) [Preview Abstract] |
Sunday, October 16, 2016 10:42AM - 10:54AM |
PG.00002: The nucleon-nucleon interaction up to sixth order in the chiral expansion Ruprecht Machleidt, Yevgen Nosyk We have calculated the nucleon-nucleon potential up to sixth order (N5LO) of chiral perturbation theory[1,2]. Previous calculations extended only up to N3LO (fourth order)[3] and typically showed a surplus of attraction, particularly, when the $\pi$-$N$ LECs from $\pi$-$N$ analysis were applied consistently. Furthermore, the contributions at N2LO and N3LO are both fairly sizeable, thus, raising concerns about the convergence of the chiral expansion. We show that the N4LO contribution is repulsive and, essentially, cancels the excessive attraction of N3LO. The N5LO contribution turns out to be considerably smaller than the N4LO one, hence establishing the desired trend of convergence. The predictions at N5LO are in excellent agreement with the empirical phase shifts of peripheral partial waves. \\ 1. D. R. Entem, N. Kaiser, R. Machleidt, and Y. Nosyk, Phys. Rev. C 91, 014002 (2015). \\ 2. D. R. Entem, N. Kaiser, R. Machleidt, and Y. Nosyk, Phys. Rev. C 92, 064001 (2015). \\ 3. R. Machleidt and D. R. Entem, Phys. Reports 503, 1 (2011). [Preview Abstract] |
Sunday, October 16, 2016 10:54AM - 11:06AM |
PG.00003: Separable Multichannel Momentum Space Potentials for Nuclear Reactions Linda Hlophe, Charlotte Elster Many nuclei are deformed and their properties can be described using a rotational model. This involves defining a deformed surface of the nucleus and constructing the nucleon-nucleus interaction as a function of distance to the surface. Such a potential has non-zero matrix elements between different nuclear rotational states which are characterized by the spin-parity $I^\pi$, leading to channel couplings. For specific reaction calculations, it is advantageous to have separable representations of the interaction matrix elements available. We develop separable representations following a scheme suggested by Ernst, Shakin, and Thaler (EST). Since optical potentials are complex and energy-dependent, the multichannel EST scheme is generalized to complex, energy-dependent separable potentials. In the case of proton-nucleus interactions the EST scheme is further extended to include charged particles. The multichannel EST scheme is applied to nucleon scattering off $^{12}$C, where the first two excited states $(I^\pi=2^+ ,4^+)$ are taken into account. [Preview Abstract] |
Sunday, October 16, 2016 11:06AM - 11:18AM |
PG.00004: ABSTRACT WITHDRAWN |
Sunday, October 16, 2016 11:18AM - 11:30AM |
PG.00005: Results for p-shell nuclei at LO, NLO, and N2LO in chiral EFT Pieter Maris, James Vary We present results for $p$-shell nuclei [1] using interactions derived from chiral effective field theory [2] up to N$^2$LO. The many-body calculations are performed order-by-order in the chiral expansion. We show the dependence of the ground state energies on the chiral order; we also present excitation energies of narrow excited states and other observables such as magnetic and quadrupole moments of selected ground states. We discuss both the theoretical uncertainties due to the truncation of the chiral expansion [2], as well as the numerical uncertainties associated with the many-body method.\\\relax [1] S.~Binder {\it et al.}, Phys.~Rev.~C93, 044002 (2016).\\\relax [2] E.~Epelbaum, H.~Krebs and U.-G.~Mei\ss ner, Phys.~Rev.~Lett.~115, 122301 (2015).\\\relax [Preview Abstract] |
Sunday, October 16, 2016 11:30AM - 11:42AM |
PG.00006: Static and dynamic screening effect on the resonant alpha-alpha scattering in a QED plasma Xiaojun Yao, Thomas Mehen, Berndt Mueller The plasma screening effect on the low-energy $\alpha-\alpha$ ($^4$He$-$$^4$He) scattering is studied by using the pionless effective field theory and thermal field theory. It is known that in vacuum a resonance lies at the center-of-mass energy 91.84 keV with a width 5.57 eV, identified as the ground state of $^8$Be. It is found that the static (Debye) screening decreases the resonance energy and width. A bound state starts to form when $m_D>0.3$ MeV. However, when the dynamic screening effect is included, which results in an imaginary potential (damping rate), both the resonance energy and width increase with the plasma temperature. Then the screening effect on the thermal nuclear scattering rate is studied and found to suppress the rate by more than 800 times when the temperature is 10 keV around. These screening effects may have implications on the rates of nuclear reactions with a resonance in the thermal domain, many of which are of great interest in cosmology and astrophysics. [Preview Abstract] |
Sunday, October 16, 2016 11:42AM - 11:54AM |
PG.00007: Amplitudes and overlaps in ab initio calculations of light nuclei Kenneth Nollett Some clustering properties of nuclei are usefully interpreted in terms of overlap functions. These functions are projections of an $A$-body nucleus onto an $(A-1)$-body core and an additional nucleon, or an $(A-4)$-body core and an additional alpha particle, at varying separation. Long-range limits of overlaps are given by asymptotic normalization constants (ANCs), which suffice to model some reaction processes; their shorter-range parts are also needed to interpret some types of experiments. Naively, one computes overlaps from wave functions using their definition. However, there is an integral relation that allows more accurate calculations from approximate wave functions, using exact terms from the nucleon-nucleon potential. I will describe calculations by this method of overlap functions and ANCs for both nucleon and alpha emission from \textit{ab initio} variational Monte Carlo wave functions. I will also describe the use of overlaps to probe small components of wave functions like those arising from hadronic parity violation. [Preview Abstract] |
Sunday, October 16, 2016 11:54AM - 12:06PM |
PG.00008: Ab initio description of continuum effects in A=11 exotic systems with chiral NN+3N forces Angelo Calci, Petr Navratil, Robert Roth, Jeremy Dohet-Eraly, Sofia Quaglioni, Guillaume Hupin Based on the fundamental symmetries of QCD, chiral effective field theory (EFT) provides two- (NN), three- (3N) and many-nucleon interactions in a consistent and systematically improvable scheme. The rapid developments to construct divers families of chiral NN+3N interactions and the conceptual and technical improvements of ab initio many-body approaches pose a great opportunity for nuclear physics. By studying particular interesting phenomena in nuclear structure and reaction observables one can discriminate between different forces and study the predictive power of chiral EFT. The accurate description of the ${}^{11}$Be nucleus, in particular, the ground-state parity inversion and exceptionally strong E1 transition between its two bound states constitute an enormous challenge for the developments of nuclear forces and many-body approaches. We present a sensitivity analysis of structure and reaction observables to different NN+3N interactions in $^{11}$Be and n+${}^{10}$Be as well as the mirror p+${}^{10}$C scattering using the ab initio NCSM with continuum (NCSMC). [Preview Abstract] |
Sunday, October 16, 2016 12:06PM - 12:18PM |
PG.00009: Fermion Mass Renormalization Using Time-dependent Relativistic Quantum Mechanics and Statistical Regularization Timothy Kutnink, Amelia Santrach, Sarah Hockett, Scott Barcus, Athanasios Petridis The time-dependent electromagnetically self-coupled Dirac equation is solved numerically by means of the staggered-leap-frog algorithm with reflecting boundary conditions. The stability region of the method versus the interaction strength and the spatial-grid size over time-step ratio is established. The expectation values of several dynamic operators are then evaluated as functions of time. These include the fermion and electromagnetic energies and the fermion dynamic mass, as the self-interacting spinors are no longer mass-eigenfunctions. There is a characteristic, non-exponential, oscillatory dependence leading to asymptotic constants of these expectation values. In the case of the fermion mass this amounts to renormalization. The dependence of the expectation values on the spatial-grid size is evaluated in detail. Statistical regularization, employing a canonical ensemble whose temperature is the inverse of the grid size, is used to remove the grid-size dependence and produce a finite result in the continuum limit. [Preview Abstract] |
Sunday, October 16, 2016 12:18PM - 12:30PM |
PG.00010: Triplet pairing in pure neutron matter SARATH SRINIVAS, Sunethra Ramanan We study the zero temperature BCS gaps for the triplet channel in pure neutron matter using Similarity Renormalization Group (SRG) evolved interactions. We use the dependence of the results on the SRG resolution scale, as a tool to analyze medium and many-body corrections. In particular, we study the effects of including the three-body interactions at leading order, which appear at N2LO in the Chiral EFT, as well as that of the first-order self-energy corrections on the zero temperature gap. In addition we also extract the transition temperature as a function of densities and verify the BCS scaling of the zero temperature gaps to the transition temperature. We observe that the self-energy effects are very crucial in order to reduce the resolution scale dependence of the results, while the three-body effects at the leading order do not change the two-body resolution scale depdendence. On the other hand, the results depend strongly on the three-body cut-off, emphasizing the importance of the missing higher-order three-body effects. We also observe that self-energy effects reduce the overall gap as well as shift the gap closure to lower densities. [Preview Abstract] |
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