Nuclear Theory·nucl-th

Tuesday·April 12, 2016

10 papers—8 primary·2 cross-listed

01
Low-energy theorems for nucleon-nucleon scattering at $M_{π} = 450$ MeV
V. Baru · E. Epelbaum · A. A. Filin
We apply the low-energy theorems to analyze the recent lattice QCD results for the two-nucleon system at a pion mass of $M_{π} ≃ 450$ MeV obtained by the NPLQCD collaboration. We find that the binding energies of the deuteron and dineutron are inconsistent with the low-energy behavior of the corresponding phase shifts within the quoted uncertainties and vice versa. Using the binding energies of the deuteron and dineutron as input, we employ the low-energy theorems to predict the phase shifts and extract the scattering length and the effective range in the $^{3} S_{1}$ and $^{1} S_{0}$ channels. Our results for these quantities are consistent with those obtained by the NPLQCD collaboration from effective field theory analyses but are in conflict with their determination based on the effective-range approximation.
nucl-thhep-lathep-phPRC(2016)·31 citations
02
In Search of a Pristine Signal for (Scale-)Chiral Symmetry in Nuclei
Mannque Rho🇫🇷
I describe the long-standing search for a "smoking-gun" signal for the manifestation of (scale-)chiral symmetry in nuclear interactions. It is prompted by Gerry Brown's last unpublished note, reproduced verbatim below, on the preeminent role of pions and vector ( $ρ$ , $ω$ ) mesons in providing a simple and elegant description of strongly correlated nuclear interactions. In this note written in tribute to Gerry Brown, I first describe a case of an unambiguous signal in axial-charge transitions in nuclei and then combine his ideas with the more recent development on the role of hidden symmetries in nuclear physics. What transpires is the surprising conclusion that the Landau-Migdal fixed point interaction $G_{0}^{'}$ , the nuclear tensor forces and Brown-Rho scaling, all encoded in scale-invariant hidden local symmetry, as Gerry put, "run the show and make all forces equal."
nucl-thhep-phIJMPE(2017)·8 citations
03
The $a_{0} (980)$ and $Λ (1670)$ in the $Λ_{c}^{+} \to π^{+} η Λ$ decay
Ju-Jun Xie🇨🇳 · Li-Sheng Geng🇨🇳
We propose to study the $a_{0} (980)$ and the $Λ (1670)$ resonances in the $Λ_{c}^{+} \to π^{+} η Λ$ decay via the final state interactions of the $π^{+} η$ and $η Λ$ pairs. The weak interaction part proceeds through the $c$ quark decay process: $c (u d) \to (s + u + d ˉ) (u d)$ , while the hadronization part takes place in two different mechanisms. In the first mechanism, the $s u d$ cluster picks up a $q q ˉ$ pair from the vacuum to form the $η Λ$ meson-baryon pair while the $u d ˉ$ pair from the weak decay hadronizes into a $π^{+}$ . In the second, the $s u d$ cluster turns into a $Λ$ , while the $u d ˉ$ pair from the $c$ decay picks up a $q q ˉ$ pair and hadronizes into a meson-meson pair ( $π η$ or $K K ˉ$ ). Because the final $π^{+} η$ and $η Λ$ states are in pure isospin $I = 1$ and $I = 0$ combinations, the $Λ_{c}^{+} \to π^{+} η Λ$ decay can be an ideal process to study the $a_{0} (980)$ and $Λ (1670)$ resonances. Describing the final state interaction in the chiral unitary approach, we find that the $π^{+} η$ and $η Λ$ invariant mass distributions, up to an arbitrary normalization, show clear cusp and peak structures, which can be associated with the $a_{0} (980)$ and $Λ (1670)$ resonances, respectively. The proposed mechanism can provide valuable information on the nature of these resonances and can in principle be test by facilities such as BEPCII.
nucl-thhep-phEPJC(2016)·43 citations
04
Ferro-deformation and shape coexistence over the nuclear chart: 28 < protons (Z) < 50 and 40 < neutrons (N) < 70
Chang-Bum Moon
With the experimental data at the national nuclear data center, NNDC, we investigate systematically the emerging nuclear structure properties in the first 2+ excited energies, E(2+) and their energy ratios to the first 4+ levels, R = E(4+)/E(2+) in the nuclei over 28 < Z < 50 for protons, and 40 < N < 70 for neutrons. By introducing the pseudo-shell configurations built on the combined subshells, we explain the following phenomena; a semi-double shell closure, a shape phase transition, and a reinforced deformation. The reinforced deformation arises suddenly at Z = 40 (or 38), N = 60 and approaches a maximum value, R = 3.3, as being centered at Z = 40, N = 64. We define this reinforced deformation 'a ferro-deformation', as in the previous study [arXiv:1604.01017]. The shape coexistence would be expected to be, as forming a ferro-deformation, with a strong rotational mode, and a near spherical shape, with a vibrational mode, in the transitional region at N = 58, 60, and 62 for the nuclei, with Z = 38 and 40; 96Sr, 98Sr, 100Sr, and 98Zr, 100Zr, and 102Zr. We suggest that the ferro-deformation should be closely associated with a strong spin-orbital interaction between neutrons in the g7/2 orbital and protons in the g9/2 orbital. Such an isospin dependent spin-orbital interaction, with the same angular momentum, l = 4, reinforces nuclear surface toward a sudden and dramatic deformation, giving rise to the ferro-deformation at the critical point, Z = 40, N = 64. We discuss the similarities and differences of the ferro-deformation between the two critical points; Z = 40, N = 64 and Z = 64, N = 104.
nucl-thnucl-ex4 citations
05
Flavour dependence of the pion and kaon form factors and parton distribution functions
Parada T. P. Hutauruk🇦🇺 · Ian C. Cloet🇺🇸 · Anthony W. Thomas🇦🇺
The separate quark flavour contributions to the pion and kaon valence quark distribution functions are studied, along with the corresponding electromagnetic form factors in the space-like region. The calculations are made using the solution of the Bethe-Salpeter equation for the model of Nambu and Jona-Lasinio with proper-time regularization. Both the pion and kaon form factors and the valence quark distribution functions reproduce many of the features of the available empirical data. The larger mass if the strange quark naturally explains the empirical fact that the ratio $u_{K^{+}} (x) / u_{π^{+}} (x)$ drops below unity at large $x$ , with a value of approximately $M_{u}^{2} / M_{s}^{2}$ as $x \to 1$ . With regard to the elastic form factors we report a large flavour dependence, with the $u$ -quark contribution to the kaon form factor being an order of magnitude smaller than that of the $s$ -quark at large $Q^{2}$ , which may be a sensitive measure of confinement effects in QCD. Surprisingly though, the total $K^{+}$ and $π^{+}$ form factors differ by only 10\%.
nucl-thhep-phPRC(2016)·86 citations
06
Numerical study of renormalization group flows of nuclear effective field theory without pions on a lattice
Koji Harada🇯🇵 · Satoru Sasabe🇯🇵 · Masanobu Yahiro🇯🇵
We formulate the next-to-leading order nuclear effective field theory without pions in the two-nucleon sector on a spatial lattice, and investigate nonperturbative renormalization group flows in the strong coupling region by diagonalizing the Hamiltonian numerically. The cutoff (proportional to the inverse of the lattice constant) dependence of the coupling constants is obtained by changing the lattice constant with the binding energy and the asymptotic normalization constant for the groundstate being fixed. We argue that the critical line can be obtained by looking at the finite-size dependence of the groundstate energy. We determine the relevant operator and locate the nontrivial fixed point, as well as the physical flow line corresponding to the deuteron in the two-dimensional plane of dimensionless coupling constants. It turns out that the location of the nontrivial fixed point is very close to the one obtained by the corresponding analytic calculation, but the relevant operator is quite different.
nucl-thPRC(2016)·3 citations
07
Study of the Pion-Nucleon Coupling Constant Charge Dependence on the Basis of the Low-Energy Data on Nucleon-Nucleon Interaction
V. A. Babenko🇺🇦 · N. M. Petrov🇺🇦
We study relationship between the physical quantities that characterize pion-nucleon and nucleon-nucleon interaction on the basis of the fact that nuclear forces in the nucleon-nucleon system at low energies are mainly determined by the one-pion exchange mechanism. By making use of the recommended proton-proton low-energy scattering parameters, we obtain the following value for the charged pion-nucleon coupling constant g $_{π^{\pm}}^{2} /4 π = 14.55 (13)$ . Calculated value of this quantity is in excellent agreement with the experimental result g $_{π^{\pm}}^{2} /4 π = 14.52 (26)$ of the Uppsala Neutron Research Group. At the same time, the obtained value of the charged pion-nucleon coupling constant differs markedly from the value of the neutral pion-nucleon coupling constant g $_{π^{0}}^{2} /4 π = 13.55 (13)$ . Thus, our results show considerable charge splitting of the pion-nucleon coupling constant.
nucl-thhep-ph8 citations
08
$N^{*}$ Resonances in Lattice QCD from (mostly) Low to (sometimes) High Virtualities
David Richards🇺🇸
I present a survey of calculations of the excited $N^{*}$ spectrum in lattice QCD. I then describe recent advances aimed at extracting the momentum-dependent phase shifts from lattice calculations, notably in the meson sector, and the potential for their application to baryons. I conclude with a discussion of calculations of the electromagnetic transition form factors to excited nucleons, including calculations at high $Q^{2}$ .
nucl-thhep-latFew Body Syst.(2016)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE