Nuclear Theory·nucl-th

Friday·November 22, 2019

8 papers—6 primary·2 cross-listed

01
Unmixing symmetries
Calvin W. Johnson
The low-lying spectra of atomic nuclei display diverse behaviors, for example rotational bands, which can be described phenomenologically by simple symmetry groups such as spatial SU(3). This leads to the idea of dynamical symmetry, where the Hamiltonian commutes with the Casimir operator(s) of a group, and is block-diagonal in subspaces defined by the group's irreducible representations or irreps. Detailed microscopic calculations, however, show these symmetries are in fact often strongly mixed and the wave function fragmented across many irreps. More commonly the fragmentation across members of a band are similar, or a quasi-dynamical symmetry. In this Letter I explicitly, albeit numerically, construct unitary transformations from a quasi-dynamical symmetry to a dynamical symmetry, adapting the similarity renormalization group, or SRG. The standard SRG produces unsatisfactory results, forcing the induced dynamical symmetry to be dominated by high-weight irreps irrespective of the original decomposition. Using spectral distribution theory to rederive and diagnose standard SRG, I introduce a new form of SRG. The new SRG transforms a quasi-dynamical symmetry to a dynamical symmetry, that is, unmixes the mixed symmetries, with intuitively more appealing results.
nucl-thPRL(2020)·5 citations
02
Masses of Light and Heavy Mesons and Baryons: A Unified Picture
L. X. Gutiérrez-Guerrero🇲🇽 · Adnan Bashir🇲🇽 · Marco A. Bedolla🇲🇽 · E. Santopinto🇮🇹
We compute masses of positive parity spin- $1/2$ and $3/2$ baryons composed of $u$ , $d$ , $s$ , $c$ and $b$ quarks in a quark-diaquark picture. The mathematical foundation for this analysis is implemented through a symmetry-preserving Schwinger-Dyson equations treatment of a vector-vector contact interaction, which preserves key features of quantum chromodynamics, such as confinement, chiral symmetry breaking and low energy Goldberger-Treiman relations. This study requires a computation of diquark correlations containing these quarks which in turn are readily inferred from solving the Bethe-Salpeter equations of the corresponding mesons. Therefore, it serves as a unified formalism for a multitude of mesons and baryons. It builds on our previous works on the study of masses, decay constants and form factors of quarkonia and light mesons, employing the same model. We use two sets of parameters, one which remains exactly the same for both the light and heavy sector hadrons, and another where the coupling strength is allowed to evolve according to the available mass scales of quarks. Our results are in very good agreement with the existing experimental data as well as predictions of other theoretical approaches whenever comparison is possible.
nucl-thhep-phPRD(2019)·78 citations
03
Fission of super-heavy elements: $^{132}$ Sn-plus-the-rest, or $^{208}$ Pb-plus-the-rest ?
C. Ishizuka · X. Zhang · M.D. Usang · F.A. Ivanyuk · S. Chiba
In this work we try to settle down the controversial predictions on the effect of doubly magic nuclei $^{132}$ Sn and $^{208}$ Pb on the mass distributions of fission fragments of super-heavy nuclei. For this we have calculated the mass distribution of super-heavy nuclei from $^{286}$ Cn to $^{306}$ 122 within the dynamical 4-dimensional Langevin approach. We have found that in "light" super-heavies the influence of $^{208}$ Pb on the mass distributions is present but negligible small. In "heavy" super-heavies, Z=120-122, the (quasi)symmetric peaks and strongly asymmetric peaks at fragment mass $A_{F}$ close to $A_{F}$ =208 are of comparable magnitude.
nucl-thastro-ph.HEnucl-exPRC(2020)·20 citations
04
The PHQMD model for the formation of nuclear clusters and hypernuclei in heavy-ion collisions
V. Kireyeu🇷🇺 · J. Aichelin🇫🇷 · E. Bratkovskaya🇩🇪 · A. Le Fèvre🇩🇪 · V. Lenivenko🇷🇺 · V. Kolesnikov🇷🇺 · Y. Leifels🇩🇪 · V. Voronyuk🇷🇺
Modeling of the process of the formation of nuclear clusters in the hot nuclear matter is a challenging task. We present the novel n-body dynamical transport approach - PHQMD (Parton-Hadron-Quantum-Molecular Dynamics) [1] for the description of heavy-ion collisions as well as clusters and hpernuclei formation. The PHQMD extends well established PHSD (Parton-Hadron-String Dynamics) approach - which incorporates explicit partonic degrees-of-freedom (quarks and gluons), an equation-of-state from lattice QCD, as well as dynamical hadronization and hadronic elastic and inelastic collisions in the final reaction phase, by n-body quantum molecular dynamic propagation of hadrons which allows choosing of the equation of state with different compression modulus. The formation of clusters, including hypernuclei, is realized by incorporation the Simulated Annealing Clusterization Algorithm (SACA). We present first results from PHQMD on the study of the production rates of strange hadrons, nuclear clusters and hypernuclei in e1elementary and heavy-ion collisions at NICA energies. In particular, sensitivity on the "hard" and "soft" equation of state within the PHQMD model was investigated for "bulk" observables.
nucl-thhep-phBull.Russ.Acad.Sci.Phys.(2020)·6 citations
05
Importance of chiral constraints for the pole content of the $K ˉ N$ scattering amplitude
P. C. Bruns🇨🇿 · A. Cieplý🇨🇿
We critically examine the $K ˉ N$ coupled-channel approach presented in [1] and demonstrate that it violates constraints imposed by chiral symmetry of QCD. The origin of this violation can be traced back to the off-shell treatment of the chiral-effective vertices, in combination with the use of non-relativistic approximations and the chosen regularization scheme. We propose an improved version of the approach, which is directly given by a resummation of relativistic Feynman graphs of baryon chiral perturbation theory, and is in accord with the chiral symmetry constraint. Within this improved model, two poles are generated dynamically in the isoscalar $π Σ - K ˉ N$ coupled channels sector, in contrast with the non-relativistic model of [1] in which only one such pole was reported.
nucl-thNPA(2020)·12 citations
06
NN scattering and nuclear uncertainties
Enrique Ruiz Arriola🇪🇸 · Jose Enrique Amaro🇪🇸 · Rodrigo Navarro Perez🇺🇸
Ab initio calculations in Nuclear physics for atomic nuclei require a specific knowledge of the interactions among their constituents, protons and neutrons. In particular, NN interactions can be constrained down to scale resolutions of $Δ r \sim 0.6 fm$ from the study of phase shifts below the pion production threshold. However, this allows for ambiguities and uncertainties which have an impact on finite nuclei, nuclear- and neutron-matter properties. On the other hand the nuclear many body problem is intrinsically difficult and the computational cost increases with numerical precision and number of nucleons. However, it is unclear what the physical precision should be for these calculations. In this contribution we review much of the work done in Granada to encompass both the uncertainties stemming from the NN scattering database in light nuclei such as triton and alpha particle and the numerical precision required by the solution method.
nucl-thhep-phFront.in Phys.(2020)·17 citations
07
Experimental validation of the theoretical prediction for the optical $S$ matrix
A.M. Martínez-Argüello · V. Domínguez-Rocha · R.A. Méndez-Sánchez · M. Martínez-Mares
Scattering of waves is omnipresent in nature in systems with sizes varying from $1 0^{- 15}$ to $1 0^{25}$ m. Within this 40 orders of magnitude, in a great number of systems, the scattering can be separated in an averaged response that crosses rapidly the scattering region and a fluctuating delayed response. This fact is the basis of the optical model; the averaged response, represented by the optical matrix $⟨ S ⟩$ , is composed with the fluctuating part that can be taken as a random matrix. Although the optical model was developed more than 60 years ago, a theoretical prediction for the optical matrix was obtained until very recently. The validity of such prediction is experimentally demonstrated here. This is done studying the scattering of torsional waves in a quasi-1D elastic system in which a locally periodic system is built; the distribution of the scattering matrix is calculated completely free of parameters. In contradistinction to all previous works, in microwaves and in elasticity, in which the value of $⟨ S ⟩$ is obtained from the experiment, here the theoretical prediction is used to compare with the experiment. Numerical simulations show that the theoretical value is still valid when strong disorder is present. Several applications of the theoretical expression for the optical matrix in other areas of physics are proposed. Possible extensions of this work are also discussed.
↳ cond-mat.dis-nncond-mat.mtrl-scinlin.CDnucl-thPRB(2020)·0 citations
08
Axial-vector weak coupling at medium momentum for astro neutrinos and double beta decays
Hiroyasu Ejiri🇯🇵
Neutrino nuclear responses associated with medium momentum transfer of q=20-80 MeV for astro neutrinos and double beta decays were studied by using charge exchange reactions on Te128 and Te130. Gamow-Teller and spin dipole nuclear matrix elements are found to be reduced with respect to the pnQRPA matrix elements by the coefficient of around 0.35. The reduction is discussed in terms of the quenching of axial vector coupling (g_A).
↳ nucl-exnucl-thJ.Phys.G(2019)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE