Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Z13: Nuclear Theory IIILive
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Sponsoring Units: DNP Chair: Zohreh Davoudi, U of Maryland |
Tuesday, April 20, 2021 3:45PM - 3:57PM Live |
Z13.00001: Benchmarking projected Hartree-Fock as an approximation Stephanie Lauber, Calvin Johnson, Hayden Frye We benchmark angular-momentum projected Hartree-Fock calculations as an approximation to full configuration-interaction results in a shell model basis. For such a simple approximation we find reasonably good agreement between excitation spectra, including for add-A and odd-odd nuclei. Key to this, we argue, is the use of gradient descent. We also find cases where shape-coexistence demonstrably improves the spectrum and make an application to Ge nuclei and experimental results in 40Mg. [Preview Abstract] |
Tuesday, April 20, 2021 3:57PM - 4:09PM Live |
Z13.00002: Spectral signatures of collectivity in heavy nuclei in the shell model Monte Carlo method Sohan Vartak, Yoram Alhassid, Marco Bonett-Matiz Spectral signatures of the crossover from vibrational to rotational collectivity in heavy nuclei are well known. However, a microscopic description of these spectral signatures in the framework of the configuration-interaction shell model is still lacking because of the large dimensionality of the many-particle model space. The shell model Monte Carlo (SMMC) method enables calculations in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods. While SMMC is a powerful technique to calculate thermal and ground-state observables, it has been a major challenge to obtain information on individual excited states. A method was recently introduced to calculate in SMMC a few many-body energy levels for each spin and parity [1]. The method is based on a generalized eigenvalue problem satisfied by the imaginary-time response matrices of one-body densities. We apply the method to chains of heavy isotopes and find spectral signatures of collectivity that are consistent with the results of phenomenological models. The method can also be used to extract information on one-body transition densities between the ground state and the corresponding excited states. [1] Y. Alhassid, M. Bonett-Matiz and C.N. Gilbreth, to be published. [Preview Abstract] |
Tuesday, April 20, 2021 4:09PM - 4:21PM Live |
Z13.00003: Characterizing the Dynamics of Quantum Equilibration, Dissipation, and Fluctuation via Nuclear Collisions Kyle Godbey, Cedric Simenel, Sait Umar In an effort to better understand the complex nature of quantum equilibration and dissipation processes in interacting many-body systems, we have performed a systematic analysis of a large number of independent microscopic studies of collisions between atomic nuclei. Universal timescales are uncovered for each of the processes which suggest a limit to the possible interplay between mechanisms. The quickest processes are that of neutron-to-proton equilibration, kinetic energy dissipation, and angular momentum dissipation -- all on the order of $10^{-21}$s. This is much faster than the characteristic timescale of mass equilibration, which has a general equilibration time of $2\times 10^{-20}$s, indicating that mass equilibration is not a primary driver of dissipation processes. Instead, it is the initial neutron-to-proton equilibration (itself a transfer of particles) that generates much of the dissipation. \newline \newline [1] C. Simenel, K. Godbey, and A.S. Umar, Phys. Rev. Lett. 124, 212504 [Preview Abstract] |
Tuesday, April 20, 2021 4:21PM - 4:33PM Live |
Z13.00004: Spectroscopic factors in threshold nuclei Joshua Wylie, Simin Wang, Xingze Mao, Witold Nazarewicz Single-nucleon knockout cross sections have recently been studied experimentally in nuclei around the proton drip-line. The experimental data were interpreted in terms of shell-model and variational Monte Carlo spectroscopic factors (SFs); however, the strong suppression of experimental SFs was not confirmed by theory. To see whether this disagreement can be attributed to the particle continuum effects, in this work, we applied the Gamow Shell Model to investigate the SFs of $^9$C and $^9$Li for single-nucleon knockout reactions in which well-bound nucleons are removed. Our calculations yield SFs that are indeed strongly reduced due to continuum coupling. [Preview Abstract] |
Tuesday, April 20, 2021 4:33PM - 4:45PM Live |
Z13.00005: Constraining the nonanalytic terms in the isospin-asymmetry expansion of nuclear equation of state Pengsheng Wen, Jeremy Holt The nuclear symmetry energy, defined as the difference of the energy per particle between the pure neutron matter and the symmetric nuclear matter at a fixed density, is crucial for understanding the properties of neutron-rich nuclei and neutron stars. The expansion of the nuclear symmetry energy in even powers of the isospin asymmetry has recently been shown to breakdown in beyond-mean-field-theory calculations of the nuclear equation of state. In this talk we will describe a new finite difference method to extract the fourth- and sixth-order regular and logarithmic contributions to the nuclear symmetry energy with microscopic chiral two- and three-body forces. We find that in general the expansion coefficients of the nonanalytic logarithm terms are larger in magnitude than those of the corresponding regular terms (even-power) for the energy from the second-order perturbation calculation. But overall, the normal terms give larger contributions to the ground state energy. The high-order terms are important to describe the proton fraction in the beta-equilibrium nuclear matter. Different chiral potentials produce different values of those coefficients, which results in uncertainties of the tendency of the proton fraction at the high-density region. [Preview Abstract] |
Tuesday, April 20, 2021 4:45PM - 4:57PM Live |
Z13.00006: Fitting protocols, statistical errors, and parametric correlations in covariant energy density functionals Ahmad Taninah, Anatoli Afanasjev, Sylvester Agbemava Statistical errors in ground state observables of spherical even-even nuclei and their propagation to the limits of nuclear landscape have been investigated in covariant density functional theory (CDFT) for the first time. In this study we consider only covariant energy density functionals with nonlinear density dependency. Statistical errors for binding energies and neutron skins significantly increase on approaching the two-neutron drip line [1]. On the contrary, such a trend does not exist for statistical errors in charge radii and two-neutron separation energies [1]. Statistical errors in the description of physical observables related to the ground state and single-particle degrees of freedom are typically substantially lower in CDFT as compared with Skyrme density functional theory. The parametric correlations between model parameters are studied in several classes of covariant density functional theory; their removal allows to reduce the number of independent parameters in the functionals to 5 or 6 [1,2]. [1] S. E. Agbemava, A. V. Afanasjev, and A. Taninah, Phys. Rev. C 99, 014318 (2019). [2] A. Taninah, S. E. Agbemava, A. V. Afanasjev, and P. Ring, Phys. Lett. B 800, 135065 (2020). [Preview Abstract] |
Tuesday, April 20, 2021 4:57PM - 5:09PM Live |
Z13.00007: Renormalization of fermion-mass and charge using the relativistic, time-dependent Dirac equation. Timothy Kutnink, David Atri-Schuller, Zachary Fisher, Christian McMurray, Sarah Hockett, Amelia Santrach, Scott Barcus, Athanasios Petridis The time-dependent electromagnetically self-coupled Dirac equation is solved numerically by means of the staggered-leap-frog algorithm with a stability region established. The expectation values of several dynamic operators are evaluated as functions of time. These include the fermion and electromagnetic energies, the fermion dynamic mass, and contributions of positive and negative energy states to the norm. There is a characteristic time-dependence leading to asymptotic constants of these expectation values. In the case of the fermion mass and charge this amounts to renormalization. The dependence of the expectation values on the spatial-grid size is evaluated and yields finite results due to the finiteness and continuity of the spinor. A statistical method, employing a canonical ensemble whose temperature is the inverse of the spatial-grid size, is used to remove the momentum-dependence. A result for each spatial-grid size value is obtained. The continuum limit is taken to calculate both the fermion mass and charge. The renormalization mass correction is 10{\%} and the charge correction is about 5{\%}. [Preview Abstract] |
Tuesday, April 20, 2021 5:09PM - 5:21PM Live |
Z13.00008: All types of Masses And Mass Groups, Upon Creation, Will Exhibit No Motion, Linear, Rotational And/Or Vibrational Motion, Singly Or In Some Combination, Which May Later Be Altered By External Forces: A Natural Law Stewart Brekke In 1905 in his Special Theory of Relativity Einstein suggested that the total energy of any mass at slow speeds was described by the relation $E=mc^2 + 1/2mv^2$. At that time it was not even certain that atoms and molecules even existed ad the only universal motion that could be observed in all masses was either linear motion or no motion. It could sometimes be observed that masses and mass groups could also be rotating and vibrating as well s moving linearly. Later in the 20th century the existence of matter in small forms such as elementary particles, nuclei, ions and molecules had been verified. However, physicists in the 1950's and 1960's discovered that other masses and mass groups such as nuclei, molecules, planets, satellites and stars also may exhibit rotational, and vibrational motion as well as linear motion or even no motion in some combination. Einstein's 1905 total energy equation for all masses and mass groups, and also many other physics equations as well, must be updated to include rotational and vibrational kinetic energy factors for accuracy. The total energy of any mass or mass group at slow speeds must now be $E=mc^2 + 1/2mv^2 + 1/2I(\omega)^2 + 1/2kx^2.$ where $(1/2)I(\omega)^2$ is the rotational kinetic energy and $(1/2)kx^2$is the kinetic energy of a simple harmonic oscillator. [Preview Abstract] |
Tuesday, April 20, 2021 5:21PM - 5:33PM Live |
Z13.00009: Electroweak axial structure functions and CKM unitarity Peter Blunden, Kyle Shiells, Wally Melnitchouk The $\gamma W$ box radiative correction is the largest source of hadronic uncertainty in the determination of the CKM matrix element $V_{ud}$ from super-allowed nuclear $\beta$-decay. The recent development of computational methods using dispersion relations allows for a systematic improvement to the calculation of the axial-vector part of the $\gamma W$ box amplitude $\Box^{\gamma W}_{A}$ in terms of the isoscalar part of the $F_3^{\gamma W}$ interference structure function, with improved and quantifiable estimates of the hadronic uncertainties. Using the latest available phenomenology for $F_3^{\gamma W}$ from the nucleon elastic, resonance, deep-inelastic, and Regge regions, we find the real part of the box correction to be \mbox{$\Box^{\gamma W}_A = 3.90(9) \times 10^{-3}$}. This gives a theoretical estimate of the CKM matrix element $|V_{ud}|^2=0.94805(26)$, which represents a 4$\sigma$ violation of unitarity. Implications for the $\gamma Z$ interference radiative corrections applicable to parity-violating electron-proton scattering are also discussed. [Preview Abstract] |
Tuesday, April 20, 2021 5:33PM - 5:45PM Live |
Z13.00010: Distribution of ratio of consecutive level spacings in interacting boson model and shell model Sofia Karampagia, Jesse Spitler, Vladimir Zelevinsky The nearest-neighbor spacing distribution in random matrix theory (RMT) ensembles has long been used for the study of quantum chaos in many-body systems. Recently, a novel measure of quantum chaos was introduced, the distribution of ratio of consecutive level spacings and expressions of this distribution were derived for the integrable case (Poisson) and the RMT ensembles (GOE, GUE, GSE). An advantage of the distribution of ratio of consecutive level spacings is that the usual unfolding procedure of the energy spectrum, in order to get an average level spacing equal to one, is no longer required. In this talk we present an expression of a distribution with a single parameter, $\lambda$, which takes the Poisson form of the distribution of ratio of consecutive level spacing when $\lambda=0$ and the RMT ensemble form when $\lambda=1$. This expression is then applied to specific cases of the Interacting Boson Model and the configuration interaction Shell Model and it is also compared to results obtained using the nearest-neighbor spacing distribution. [Preview Abstract] |
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