Nuclear Theory·nucl-th

Monday·July 31, 2017

9 papers—5 primary·4 cross-listed

01
Delta isobars and nuclear saturation
A. Ekström🇸🇪 · G. Hagen🇺🇸 · T. D. Morris🇺🇸 · T. Papenbrock🇺🇸 · P. D. Schwartz🇺🇸
We construct a nuclear interaction in chiral effective field theory with explicit inclusion of the $Δ$ -isobar $Δ (1232)$ degree of freedom at all orders up to next-to-next-to-leading order (NNLO). We use pion-nucleon ( $π N$ ) low-energy constants (LECs) from a Roy-Steiner analysis of $π N$ scattering data, optimize the LECs in the contact potentials up to NNLO to reproduce low-energy nucleon-nucleon scattering phase shifts, and constrain the three-nucleon interaction at NNLO to reproduce the binding energy and point-proton radius of $^{4}$ He. For heavier nuclei we use the coupled-cluster method to compute binding energies, radii, and neutron skins. We find that radii and binding energies are much improved for interactions with explicit inclusion of $Δ (1232)$ , while $Δ$ -less interactions produce nuclei that are not bound with respect to breakup into $α$ particles. The saturation of nuclear matter is significantly improved, and its symmetry energy is consistent with empirical estimates.
nucl-thnucl-exPRC(2018)·132 citations
02
Maris polarization in neutron-rich nuclei
Shubhchintak🇺🇸 · C.A. Bertulani🇺🇸 · T. Aumann🇩🇪
We present a theoretical study of the Maris polarization effect and its application in quasi-free reactions to assess information on the structure of exotic nuclei. We discuss the uncertainties in the calculations of triple differential cross sections and of analyzing powers due the choices of various nucleon-nucleon interactions the optical potentials and limitations of the method. Our calculations explore a large number of choices for the nucleon-nucleon (NN) interactions and the optical potential for nucleon-nucleus scattering. Our study implies that polarization variables in (p,2p) reactions in inverse kinematics can be an effective probe of single-particle structure of nuclei in radioactive-beam facilities.
nucl-thnucl-exPLB(2018)·7 citations
03
Multicomponent van der Waals equation of state: Applications in nuclear and hadronic physics
Volodymyr Vovchenko🇩🇪 · Anton Motornenko🇩🇪 · Paolo Alba🇩🇪 · Mark I. Gorenstein🇺🇦 · Leonid M. Satarov🇩🇪 · Horst Stoecker🇩🇪
A generalization of the quantum van der Waals equation of state for a multi-component system in the grand canonical ensemble is proposed. The model includes quantum statistical effects and allows to specify the parameters characterizing repulsive and attractive forces for each pair of particle species. The model can be straightforwardly applied to the description of asymmetric nuclear matter and also for mixtures of interacting nucleons and nuclei. Applications of the model to the equation of state of an interacting hadron resonance gas are discussed.
nucl-thcond-mat.stat-mechhep-phPRC(2017)·72 citations
04
Isospin-Asymmetry Dependence of the Thermodynamic Nuclear Equation of State in Many-Body Perturbation Theory
Corbinian Wellenhofer🇩🇪
The computation of the thermodynamic properties of nuclear matter is a central task of theoretical nuclear physics. The nuclear equation of state is an essential quantity in nuclear astrophysics and governs the properties of neutron stars and core-collapse supernovæ. The framework of chiral effective field theory provides the basis for the description of nuclear interactions in terms of a systematic low-energy expansion. In this thesis, we apply chiral two- and three-nucleon interactions in perturbative many-body calculations of the thermodynamic equation of state of infinite homogeneous nuclear matter. The conceptual issues that arise concerning the consistent generalization of the standard zero-temperature form of many-body perturbation theory to finite temperatures are investigated in detail. The structure of many-body perturbation theory at higher orders is examined, in particular concerning the role of the so-called anomalous contributions. The first-order nuclear liquid-gas phase transition is analyzed with respect to its dependence on temperature and the neutron-to-proton ratio. Furthermore, the convergence behavior of the expansion of the equation of state in terms of the isospin asymmetry is examined. It is shown that the expansion coefficients beyond the quadratic order diverge in the zero-temperature limit, implying a nonanalytic form of the isospin-asymmetry dependence at low temperatures. This behavior is associated with logarithmic terms in the isospin-asymmetry dependence at zero temperature.
nucl-th5 citations
05
The $α + d \to^{6} Li + γ$ astrophysical $S$ -factor and its implications for Big Bang Nucleosynthesis
A. Grassi · G. Mangano · L.E. Marcucci · O. Pisanti
The $α + d \to^{6} Li + γ$ radiative capture is studied in order to predict the $^{6}$ Li primordial abundance. Within a two-body framework, the $α$ particle and the deuteron are considered the structureless constituents of $^{6}$ Li. Five $α + d$ potentials are used to solve the two-body problem: four of them are taken from the literature, only one having also a tensor component. A fifth model is here constructed in order to reproduce, besides the $^{6}$ Li static properties as binding energy, magnetic dipole and electric quadrupole moments, also the $S$ -state asymptotic normalization coefficient (ANC). The two-body bound and scattering problem is solved with different techniques, in order to minimize the numerical uncertainty of the present results. The long-wavelength approximation is used, and therefore only the electric dipole and quadrupole operators are retained. The astrophysical $S$ -factor is found to be significantly sensitive to the ANC, but in all the cases in good agreement with the available experimental data. The theoretical uncertainty has been estimated of the order of few % when the potentials which reproduce the ANC are considered, but increases up to $≃ 20$ % when all the five potential models are retained. The effect of this $S$ -factor prediction on the $^{6}$ Li primordial abundance is studied, using the public code PArthENoPE. For the five models considered here we find $^{6} Li /$ H $= (0.9 - 1.8) \times 1 0^{- 14}$ , with the baryon density parameter in the 3- $σ$ range of Planck 2015 analysis, $Ω_{b} h^{2} = 0.02226 \pm 0.00023$ .
nucl-thPRC(2017)·21 citations
06
Quarkonium Polarization and the Long Distance Matrix Elements Hierarchies using Jet Substructure
Lin Dai🇺🇸 · Prashant Shrivastava🇺🇸
We investigate the quarkonium production mechanisms in jets at the LHC, using the Fragmenting Jet Functions (FJF) approach. Specifically, we discuss the jet energy dependence of the $J / ψ$ production cross section at the LHC. By comparing the cross sections for the different NRQCD production channels ( $^{1} S_{0}^{[8]}$ , $^{3} S_{1}^{[8]}$ , $^{3} P_{J}^{[8]}$ , and $^{3} S_{1}^{[1]}$ ), we find that at fixed values of energy fraction $z$ carried by the $J / ψ$ , if the normalized cross section is a decreasing function of the jet energy, in particular for $z > 0.5$ , then the depolarizing $^{1} S_{0}^{[8]}$ must be the dominant channel. This makes the prediction made in [Baumgart et al., JHEP 1411, 003 (2014)] for the FJF's also true for the cross section. We also make comparisons between the long distance matrix elements extracted by various groups. This analysis could potentially shed light on the polarization properties of the $J / ψ$ production in high $p_{T}$ region.
↳ hep-phnucl-thPRD(2017)·10 citations
07
Chiral symmetry constraints on resonant amplitudes
Peter C. Bruns🇩🇪 · Maxim Mai🇺🇸
We discuss the impact of chiral symmetry constraints on the quark-mass dependence of meson resonance pole positions, which are encoded in non-perturbative parametrizations of meson scattering amplitudes. Model-independent conditions on such parametrizations are derived, which are shown to guarantee the correct functional form of the leading quark-mass corrections to the resonance pole positions. Some model amplitudes for $π π$ scattering, widely used for the determination of $ρ$ and $σ$ resonance properties from results of lattice simulations, are tested explicitly with respect to these conditions.
↳ hep-latnucl-thPLB(2018)·15 citations
08
The nucleon as a test case to calculate vector-isovector form factors at low energies
Stefan Leupold (UU)🇸🇪
Extending a recent suggestion for hyperon form factors to the nucleon case, dispersion theory is used to relate the low-energy vector-isovector form factors of the nucleon to the pion vector form factor. The additionally required input, i.e. the pion-nucleon scattering amplitudes are determined from relativistic next-to-leading-order (NLO) baryon chiral perturbation theory including the nucleons and optionally the Delta baryons. Two methods how to include pion rescattering are compared: (a) solving the Muskhelishvili-Omnes (MO) equation and (b) using an N/D approach. It turns out that the results differ strongly from each other. Furthermore the results are compared to a fully dispersive calculation of the (subthreshold) pion-nucleon amplitudes based on Roy-Steiner (RS) equations. In full agreement with the findings from the hyperon sector it turns out that the inclusion of Delta baryons is not an option but a necessity to obtain reasonable results. The magnetic isovector form factor depends strongly on a low-energy constant of the NLO Lagrangian. If it is adjusted such that the corresponding magnetic radius is reproduced, then the results for the corresponding pion-nucleon scattering amplitude (based on the MO equation) agree very well with the RS results. Also in the electric sector the Delta degrees of freedom are needed to obtain the correct order of magnitude for the isovector charge and the corresponding electric radius. Yet quantitative agreement is not achieved. If the subtraction constant that appears in the solution of the MO equation is not taken from nucleon+Delta chiral perturbation theory but adjusted such that the electric radius is reproduced, then one obtains also in this sector a pion-nucleon scattering amplitude that agrees well with the RS results.
↳ hep-phnucl-thEPJA(2018)·84 citations
09
Covariant spectator theory of quark-antiquark bound states: Mass spectra and vertex functions of heavy and heavy-light mesons
Sofia Leitão🇵🇹 · Alfred Stadler🇵🇹 · M. T. Peña🇵🇹 · Elmar P. Biernat🇵🇹
We use the covariant spectator theory with an effective quark-antiquark interaction, containing Lorentz scalar, pseudoscalar, and vector contributions, to calculate the masses and vertex functions of, simultaneously, heavy and heavy-light mesons. We perform least-square fits of the model parameters, including the quark masses, to the meson spectrum and systematically study the sensitivity of the parameters with respect to different sets of fitted data. We investigate the influence of the vector confining interaction by using a continuous parameter controlling its weight. We find that vector contributions to the confining interaction between 0% and about 30% lead to essentially the same agreement with the data. Similarly, the light quark masses are not very tightly constrained. In all cases, the meson mass spectra calculated with our fitted models agree very well with the experimental data. We also calculate the mesons wave functions in a partial wave representation and show how they are related to the meson vertex functions in covariant form.
↳ hep-phnucl-thPRD(2017)·29 citations

Affiliations

first authorsco-authorsvia INSPIRE