Nuclear Theory·nucl-th

Monday·March 11, 2019

10 papers—6 primary·4 cross-listed

01
Density-dependent NN-interaction from subleading chiral 3N-forces: Long-range terms
N. Kaiser · B. Singh
We derive from the subleading contributions to the chiral three-nucleon force (long-range terms, published in Phys.\,Rev.\,C\,77, 064004 (2008)) a density-dependent two-nucleon interaction $V_{med}$ in isospin-symmetric, spin-saturated nuclear matter. Following the division of the pertinent 3N-diagrams into two-pion exchange topology, two-pion-one-pion exchange topology and ring topology, we evaluate for these all self-closings and concatenations of nucleon-lines to an in-medium loop. The momentum and $k_{f}$ -dependent potentials associated with the isospin operators ( $1$ and $τ_{1} \cdot τ_{2}$ ) and five independent spin-structures are expressed in terms of functions, which are either given in closed analytical form or require at most one numerical integration. In the same way we treat the $2 π$ -exchange 3N-force up to fourth order. Our results for $V_{med}$ are most helpful to implement the long-range subleading chiral 3N-forces into nuclear many-body calculations.
nucl-thPRC(2019)·24 citations
02
Update of a Multi-Phase Transport Model with Modern Parton Distribution Functions and Nuclear Shadowing
Chao Zhang🇨🇳 · Liang Zheng🇨🇳 · Feng Liu🇨🇳 · Shusu Shi🇨🇳 · Zi-Wei Lin🇨🇳
A multi-phase transport (AMPT) model has been successful in explaining a wide range of observables in relativistic heavy ion collisions. In this work, we implement a modern set of free proton parton distribution functions and an impact parameter-dependent nuclear shadowing in the AMPT model. After refitting the parameters of the two-component initial condition model to the experimental data on $pp$ and $p p ˉ$ total and inelastic cross sections from $s \sim$ 4 GeV to 13 TeV, we study particle productions in $pp$ and $AA$ collisions. We show that the updated AMPT model with string melting can reasonably describe the overall particle yields and transverse momentum spectra for both $pp$ and $AA$ collisions at RHIC and LHC energies after we introduce a nuclear scaling of the minijet transverse momentum cutoff for $AA$ collisions at LHC energies that is motivated by the color glass condensate. Since heavy flavor and high- $p_{T}$ particles are produced by perturbative-QCD processes and thus directly depend on parton distribution functions of nuclei, the updated AMPT model is expected to provide a more reliable description of these observables.
nucl-thhep-phnucl-exPRC(2019)·31 citations
03
Suddenly shortened half-lives beyond $^{78}$ Ni: $N = 50$ magic number and high-energy non-unique first-forbidden transitions
Kenichi Yoshida
$β$ -decay rates play a decisive role in understanding the nucleosynthesis of heavy elements and are governed by microscopic nuclear-structure information. A sudden shortening of the half-lives of Ni isotopes beyond $N = 50$ was observed at the RIKEN-RIBF. This is considered due to the persistence of the neutron magic number $N = 50$ in the very neutron-rich Ni isotopes. By systematically studying the $β$ -decay rates and strength distributions in the neutron-rich Ni isotopes around $N = 50$ , I try to understand the microscopic mechanism for the observed sudden shortening of the half-lives. The $β$ -strength distributions in the neutron-rich nuclei are described in the framework of nuclear density-functional theory. I employ the Skyrme energy-density functionals (EDF) in the Hartree-Fock-Bogoliubov calculation for the ground states and in the proton-neutron Quasiparticle Random-Phase Approximation (pnQRPA) for the transitions. Not only the allowed but the first-forbidden (FF) transitions are considered. The experimentally observed sudden shortening of the half-lives beyond $N = 50$ is reproduced well by the calculations employing the Skyrme SkM* and SLy4 functionals. The sudden shortening of the half-lives is due to the shell gap at $N = 50$ and cooperatively with the high-energy transitions to the low-lying $0^{-}$ and $1^{-}$ states in the daughter nuclei. The onset of FF transitions pointed out around $N = 82$ and 126 is preserved in the lower-mass nuclei around $N = 50$ . This study suggests that needed is a microscopic calculation where the shell structure in neutron-rich nuclei and its associated effects on the FF transitions are selfconsistenly taken into account for predicting $β$ -decay rates of exotic nuclei in unknown region.
nucl-thnucl-exPRC(2019)·13 citations
04
Mapping neutron star data to the equation of state using the deep neural network
Yuki Fujimoto🇯🇵 · Kenji Fukushima🇯🇵 · Koichi Murase🇯🇵
The densest state of matter in the universe is uniquely realized inside central cores of the neutron star. While first-principles evaluation of the equation of state of such matter remains as one of the longstanding problems in nuclear theory, evaluation in light of neutron star phenomenology is feasible. Here we show results from a novel theoretical technique to utilize deep neural network with supervised learning. We input up-to-date observational data from neutron star X-ray radiations into the trained neural network and estimate a relation between the pressure and the mass density. Our results are consistent with extrapolation from the conventional nuclear models and the experimental bound on the tidal deformability inferred from gravitational wave observation.
nucl-thastro-ph.HEhep-phPRD(2020)·143 citations
05
Multi-chiral facets in symmetry restored states: Five chiral doublets candidates in even-even nucleus $^{136}$ Nd
Y. K. Wang · F. Q. Chen · P. W. Zhao · S. Q. Zhang · J. Meng
A triaxial projected shell model including configurations with more than four quasiparticles in the configuration space is developed, and applied to investigate the recently reported five chiral doublets candidates in a single even-even nucleus $^{136}$ Nd. The energy spectra and transition probability ratios $B (M 1) / B (E 2)$ are reproduced satisfactorily. The configuration mixing along the rotational bands is studied by analyzing the intrinsic composition of the eigenfunctions. The chiral geometry of these nearly degenerate bands is examined by the \textit{K plot} and the \textit{azimuthal plot}, and the evolution from the chiral vibration to the static chirality with spin is clearly demonstrated for four pairs of partner bands. From the features in the \textit{azimuthal plot}, it is difficult to interpret the other candidate as chiral partners.
nucl-thPRC(2019)·24 citations
06
Neutrino pion-production on a nucleon
Fred Myhrer🇺🇸
Heavy baryon chiral perturbation theory ( $χ$ PT), where the $Δ$ resonance is included, is used in order to examine the axial charged-current component of the weak interaction process at low neutrino energies. At leading chiral order the Adler theorems, derived using PCAC, are satisfied. At next-to-leading chiral order this effective field theory goes beyond these theorems. I will show that $χ$ PT generates deviation from the PCAC predictions, which means that some neutrino-nucleon models that are used in evaluating neutrino nucleus scattering amplitudes, might need modifications.
nucl-thhep-phPoS(2019)·3 citations
07
Exact solution for the non-equilibrium attractor in number-conserving relaxation time approximation
Michael Strickland🇺🇸 · Ubaid Tantary🇺🇸
We extend previous studies of the conformal 0+1d kinetic non-equilibrium attractor in relaxation time approximation by enforcing number conservation through the introduction of a dynamical fugacity (chemical potential). We derive two coupled integral equations for the effective temperature and fugacity which are then solved numerically to obtain the exact solution. The resulting solutions exhibit convergence to a unique non-equilibrium attractor when the scaled moments of the distribution function are plotted as a function of the rescaled time w = tau/tau_eq. This occurs even though the system is out of chemical equilibrium at late times. In addition, compared to the case where number conservation was not imposed, we find that the moments converge to their respective attractors more quickly, particularly for moments with m=0. Finally, we compare the resulting attractor moments with predictions from different hydrodynamic frameworks.
↳ hep-phnucl-thJHEP(2019)·44 citations
08
2018 Update of the Discoveries of Nuclides
Michael Thoennessen
The 2018 update of the discovery of nuclide project is presented. 50 new nuclides were observed for the first time in 2018. A large number of isotopes is still only published in conference proceedings or internal reports.
↳ nucl-exnucl-thIJMPE(2019)·9 citations
09
The Equation of State and Cooling of Hyperonic Neutron Stars
Laura Tolos · Mario Centelles · Angels Ramos · Rodrigo Negreiros · Veronica Dexheimer
We present two recent parametrizations of the equation of state (FSU2R and FSU2H models) that reproduce the properties of nuclear matter and finite nuclei, fulfill constraints on high-density matter stemming from heavy-ion collisions, produce 2 $M_{⊙}$ neutron stars, and generate neutron star radii below 13 km. Making use of these equations of state, cooling simulations for isolated neutron stars are performed. We find that two of the models studied, FSU2R (with nucleons) and, in particular, FSU2H (with nucleons and hyperons), show very good agreement with cooling observations, even without including nucleon pairing. This indicates that cooling observations are compatible with an equation of state that produces a soft nuclear symmetry energy and, thus, generates small neutron star radii. Nevertheless, both schemes produce cold isolated neutron stars with masses above $1.8 M_{⊙}$ .
↳ astro-ph.HEnucl-th2 citations
10
Hard dilepton production from a weakly magnetized hot QCD medium
Aritra Das🇮🇳 · Najmul Haque🇮🇳 · Munshi G. Mustafa🇮🇳 · Pradip K. Roy🇮🇳
We have computed the hard dilepton production rate from a weakly magnetized deconfined QCD medium within one-loop photon self-energy by considering one hard and one thermomagnetic resummed quark propagator in the loop. In the presence of the magnetic field, the resummed propagator leads to four quasiparticle modes. The production of hard dileptons consists of rates when all four quasiquarks originating from the poles of the propagator individually annihilate with a hard quark coming from a bare propagator in the loop. Besides these, there are also contributions from a mixture of pole and Landau cut part. In weak field approximation, the magnetic field appears as a perturbative correction to the thermal contribution. Since the calculation is very involved, for a first effort as well as for simplicity, we obtained the rate up to first order in the magnetic field, i.e., $O [(e B)]$ , which causes a marginal improvement over that in the absence of magnetic field.
↳ hep-phnucl-thPRD(2019)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE