Nuclear Theory·nucl-th

Monday·February 10, 2020

10 papers—7 primary·3 cross-listed

01
Origin of the Strong Toroidal Magnetic Field in Magnetars
Naoki Onishi · Tomoyuki Maruyama
A simple model of chiral asymmetry is proposed to interpret the origin of the strong toroidal magnetic field. The electrons relevant to dynamics forming the the field are in a quantume degenerate state with ultra-relativistic Fermi energy. The system is described by Dirac Hartree Fock method using scaled h-bar method. Neutron stars are rotating and have large angular momentum which is formed by cranking model and breaks time reversal. Dirac current is decomposed into convection and spin currents due to Clifford number. The strong toroidal magnetic field is formed by the spin like current resulted by the chiral asymmetry brought about electron capture caused by the parity-violating weak interaction.
nucl-th3 citations
02
A three-dimensional momentum-space calculation of three-body bound state in a relativistic Faddeev scheme
M. R. Hadizadeh · M. Radin · K. Mohseni
In this paper, we study the relativistic effects in a three-body bound state. For this purpose, the relativistic form of the Faddeev equations is solved in momentum space as a function of the Jacobi momentum vectors without using a partial wave decomposition. The inputs for the three-dimensional Faddeev integral equation are the off-shell boost two-body $t -$ matrices, which are calculated directly from the boost two-body interactions by solving the Lippmann-Schwinger equation. The matrix elements of the boost interactions are obtained from the nonrelativistic interactions by solving a nonlinear integral equation using an iterative scheme. The relativistic effects on three-body binding energy are calculated for the Malfliet-Tjon potential. Our calculations show that the relativistic effects lead to a roughly 2\% reduction in the three-body binding energy. The contribution of different Faddeev components in the normalization of the relativistic three-body wave function is studied in detail. The accuracy of our numerical solutions is tested by calculation of the expectation value of the three-body mass operator, which shows an excellent agreement with the relativistic energy eigenvalue.
nucl-thphysics.comp-phSci.Rep.(2020)·11 citations
03
Transition properties of low-lying states in $^{28}$ Si probed via inelastic proton and alpha scattering
Yoshiko Kanada-En'yo🇯🇵 · Kazuyuki Ogata🇯🇵
$0^{+}$ , $1^{-}$ , $2^{+}$ , and $3^{-}$ excitations of $^{28} Si$ are investigated via proton and $α$ inelastic scattering off $^{28} Si$ . The structure calculation of $^{28} Si$ is performed with the energy variation after total angular momentum and parity projections in the framework of antisymmetrized molecular dynamics (AMD). As a result of the AMD calculation, the oblate ground and prolate bands, $0^{+}$ and $3^{-}$ excitations, and the $1^{-}$ and $3^{-}$ states of the $K^{π} = 0^{-}$ band are obtained. Using the matter and transition densities of $^{28} Si$ obtained by AMD, microscopic coupled-channel calculations of proton and $α$ scattering off $^{28} Si$ are performed. The proton- $^{28} Si$ potentials in the reaction calculation are microscopically derived by folding the Melbourne $g$ -matrix $N N$ interaction with the AMD densities of $^{28} Si$ . The $α$ - $^{28} Si$ potentials are obtained by folding the nucleon- $^{28} Si$ potentials with an $α$ density. The calculation reasonably reproduces the observed elastic and inelastic cross sections of proton and $α$ scattering. Transition properties are discussed by combining the reaction analysis of proton and $α$ scattering and structure features such as transition strengths and form factors. The isoscalar monopole and dipole transitions are focused.
nucl-thPRC(2020)·10 citations
04
Comparing event generator predictions and ab-initio calculations of $ν$ - $^{12}$ C neutral current quasi-elastic scattering at 1 GeV
G. B. King🇺🇸 · K. Mahn🇺🇸 · L. Pickering🇺🇸 · N. Rocco🇺🇸
The measurement of neutrino oscillations and exotic physics searches are important parts of the physics program in the near future, with new state-of-the-art experiments planned within the next decade. Future and modern experiments in these fields will make use of nuclear targets. Event Generators (EGs) are software used in the analysis of neutrino oscillation experiments. EGs use to predict kinematic observables for a range of neutrino energies. These simulations may lack physics captured by more rigorous theoretical calculations. This work compares EG performance to nuclear theory calculations by comparing observables generated in the two frameworks. We provide a common set of definitions between theory and experiment and assess the physics contained in EG simulations. Neutral current quasi-elastic (NCQE) scattering events for neutrinos and anti-neutrinos on a $^{12}$ C target are simulated with a specific EG, NEUT, used by the T2K experiment for its analysis. The simulated cross sections are compared to analytic calculations from nuclear theory within the factorization scheme. We compare the NEUT implementation of two different models on nuclear spectral functions: the Relativistic Fermi Gas (RFG) and the correlated basis spectral function (CBF) to analytic calculations of the same models in the factorization scheme. For both nuclear physics models, we compare the appearance of features in the distributions relevant to experimental analyses. Qualitatively, the shape of the simulated distribution is similar to the one obtained through theory calculations; however, there are some discrepancies between the theory calculations and the NEUT simulation. While the EG simulations and analytic calculations with the same model of nuclear dynamics show similar overall features, there are still differences between the two.
nucl-thhep-exPRC(2020)·3 citations
05
QCD equation of state at finite densities for nuclear collisions
Akihiko Monnai🇯🇵 · Björn Schenke🇺🇸 · Chun Shen🇺🇸
We construct the QCD equation of state at finite chemical potentials including net baryon, electric charge, and strangeness based on the results of lattice QCD simulations and the hadron resonance gas model. The situation of strangeness neutrality and a fixed charge-to-baryon ratio, which resembles that of heavy nuclei, is considered for the application to relativistic heavy-ion collisions. This increases the values of baryon chemical potential compared to the case of vanishing strangeness and electric charge chemical potentials, modifying the fireball trajectory in the phase diagram. We perform viscous hydrodynamic simulations and demonstrate the importance of multiple chemical potentials for identified particle production in heavy-ion collisions at the RHIC and SPS beam energy scan energies.
nucl-thhep-phnucl-exNPA(2021)·4 citations
06
Bogoliubov many-body perturbation theory under constraint
Pepijn Demol🇧🇪 · Mikael Frosini🇫🇷 · Alexander Tichai🇩🇪 · Vittorio Somà🇫🇷 · Thomas Duguet🇧🇪
In order to solve the A-body Schrödinger equation both accurately and efficiently for open-shell nuclei, a novel many-body method coined as Bogoliubov many-body perturbation theory (BMBPT) was recently formalized and applied at low orders. Based on the breaking of U(1) symmetry associated with particle-number conservation, this perturbation theory must operate under the constraint that the average number of particles is self-consistently adjusted at each perturbative order. The corresponding formalism is presently detailed with the goal to characterize the behavior of the associated Taylor series. BMBPT is, thus, investigated numerically up to high orders at the price of restricting oneself to a small, i.e. schematic, portion of Fock space. While low-order results only differ by 2 - 3 % from those obtained via a configuration interaction (CI) diagonalization, the series is shown to eventually diverge. The application of a novel resummation method coined as eigenvector continuation further increase the accuracy when built from low-order BMBPT corrections and quickly converges towards the CI result when applied at higher orders. Furthermore, the numerically-costly self-consistent particle number adjustment procedure is shown to be safely bypassed via the use of a computationally cheap a posteriori correction method. Eventually, the present work validates the fact that low order BMBPT calculations based on an a posteriori (average) particle number correction deliver controlled results and demonstrates that they can be optimally complemented by the eigenvector continuation method to provide results with sub-percent accuracy. This approach is, thus, planned to become a workhorse for realistic ab initio calculations of open-shell nuclei in the near future.
nucl-thAnnals Phys.(2021)·46 citations
07
On the excitation of the $2_{1}^{+}$ state in $^{12}$ C in the $(e, e^{'} γ)$ reaction
D. H. Jakubassa-Amundsen · V. Yu. Ponomarev
The excitation of the carbon $2^{+}$ state at 4.439 MeV by $70 - 150$ MeV electron impact and its subsequent decay to the ground state by photon emission is described within the distorted-wave Born approximation. The transition densities are obtained from the nuclear quasiparticle phonon model. The photon angular distributions are compared with earlier results and with experiment, including the influence of bremsstrahlung. Predictions for spin asymmetries in the case of polarized electron impact are also made.
nucl-thnucl-exEPJA(2020)·2 citations
08
Effective quantum kinetic theory for spin transport of fermions with collsional effects
Di-Lun Yang🇯🇵 · Koichi Hattori🇯🇵 · Yoshimasa Hidaka🇯🇵
We systematically derive the collision term for the axial kinetic theory, a quantum kinetic theory delineating the coupled dynamics of the vector/axial charges and spin transport carried by the massive spin-1/2 fermions traversing a medium. We employ the Wigner-function approach and propose a consistent power-counting scheme where the axial-charge distribution function, a non-conserved quantity for massive particles, is accounted as the first-order quantity in the $ℏ$ expansion, while the vector-charge distribution function the zeroth-order quantity. This specific power-counting scheme allows us to organize a reduced $ℏ$ expansion for the collision term and to formally identity the spin-diffusion effect and the spin-polarization effect at the same order. We confirm that the obtained collisional axial kinetic theory smoothly reduces to the chiral kinetic theory in the massless limit, serving as a consistency check. In the absence of electromagnetic fields, we further present the simplified axial kinetic equations suitable for tracking dynamical spin polarization of heavy and light fermions, respectively. As an application to the weakly coupled quark-gluon plasma at high temperature, we compute the spin-diffusion term for massive quarks within the leading-log approximation. The formal expression for the first-order terms provides a path toward evaluation of the spin polarization effect in quantum chromodynamics.
↳ hep-phhep-thnucl-thJHEP(2020)·134 citations
09
Magnetic Field in the Charged Subatomic Swirl
Xingyu Guo🇨🇳 · Jinfeng Liao🇺🇸 · Enke Wang🇨🇳
We report a novel relation between rotation and magnetic field in a charged fluid system: there is naturally a magnetic field along the direction of fluid vorticity due to the currents associated with the swirling charges. This general connection is demonstrated using a fluid vortex. Applying the idea to heavy ion collisions we propose a new mechanism for generating in-medium magnetic field with a relatively long lifetime. We estimate the magnitude of this new magnetic field in the Au-Au colliding systems across a wide span of collisional beam energy. Such a magnetic field is found to increase rapidly toward lower beam energy and could account for a significant amount of the experimentally observed global polarization difference between hyperons and anti-hyperons.
↳ hep-phnucl-thNPA(2021)·2 citations
10
Probing approach of the Parton-Hadron-String Dynamics in production for K $_{S}$ mesons
O. Kot🇺🇦 · T. Obikhod🇺🇦 · O. Okhrimenko🇺🇦 · I. Petrenko🇺🇦
Heavy ion collisions provide a unique probe of the quark-gluon plasma properties. The role of partonic degrees of freedom in p-Pb collisions at $s_{N N}$ = 5 TeV by studying the production cross section is studied. Experimental observable like the number of K $_{S}$ mesons is sensitive to the kinematic properties of the reaction. Our results demonstrate the importance of angular distribution for the partonic degrees of freedom in hadronization process.
↳ hep-phnucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE