Nuclear Theory·nucl-th

Monday·September 11, 2023

7 papers—3 primary·4 cross-listed

01
Efimov states in excited nuclear halos
Shimpei Endo · Junki Tanaka
Universality -- an essential concept in physics -- implies that different systems show the same phenomenon and can be described by a unified theory. A prime example of the universal quantum phenomena is the Efimov effect, which is the appearance of multiples of low-energy three-body bound states with progressively large sizes dictated by the discrete scale invariance. The Efimov effect, originally proposed in the nuclear physics context, has been observed in cold atoms and $^{4} He$ molecules. The search for the Efimov effect in nuclear physics, however, has been a long-standing challenge owing to the difficulty in identifying ideal nuclides with a large $s$ -wave scattering length; such nuclides can be unambiguously considered as Efimov states. Here, we propose a systematic method to identify nuclides that exhibit Efimov states in their excited states in the vicinity of the neutron separation threshold. These nuclei are characterised by their enormous low-energy neutron capture cross-sections, hence giant $s$ -wave scattering length. Using our protocol, we identified $^{90}$ Zr and $^{159}$ Gd as novel candidate nuclides that show the Efimov states. They are well inside the valley of stability in the nuclear chart, and are suited for experimental realisation of the Efimov states in nuclear physics.
nucl-thcond-mat.quant-gasnucl-ex4 citations
02
Microscopic optical potentials for medium-mass isotopes derived at the first order of the Watson multiple scattering theory
Matteo Vorabbi🇬🇧 · Carlo Barbieri🇮🇹 · Vittorio Somà🇫🇷 · Paolo Finelli🇮🇹 · Carlotta Giusti🇮🇹
We perform a first-principle calculation of optical potentials for nucleon elastic scattering off medium-mass isotopes. Fully based on a saturating chiral Hamiltonian, the optical potentials are derived by folding nuclear density distributions computed with ab initio self-consistent Green's function theory with a nucleon-nucleon $t$ matrix computed with a consistent chiral interaction. The dependence on the folding interaction as well as the convergence of the target densities are investigated. Numerical results are presented and discussed for differential cross sections and analyzing powers, with focus on elastic proton scattering off Calcium and Nickel isotopes. Our optical potentials generally show a remarkable agreement with the available experimental data for laboratory energies in the range 65-200 MeV. We study the evolution of the scattering observables with increasing proton-neutron asymmetry by computing theoretical predictions of the cross section and analyzing power over the Calcium and Nickel isotopic chains.
nucl-thnucl-exPRC(2024)·15 citations
03
Microscopic analysis of dipole electric and magnetic strengths in $^{156}$ Gd
V.O. Nesterenko · P.I. Vishnevskiy · P.-G. Reinhard · A. Repko · J. Kvasil
The dipole electric ( $E 1$ ) and magnetic ( $M 1$ ) strengths in strongly deformed $^{156}$ Gd are investigated within a fully self-consistent Quasiparticle Random Phase Approximation (QRPA) with Skyrme forces SVbas, SLy6 and SG2. We inspect, on the same theoretical footing, low-lying dipole states and the isovector giant dipole resonance in $E 1$ channel and the orbital scissors resonance as well as the spin-flip giant resonance (SFGR) in $M 1$ channel. Besides, $E 1$ toroidal mode and low-energy spin-flip $M 1$ excitations are considered. The deformation splitting and dipole-octupole coupling of electric excitations are analyzed. The origin of SFGR gross structure, impact of the residual interaction and interference of orbital and spin contributions to SFGR are discussed. The effect of the central exchange $J^{2}$ -term from the Skyrme functional is demonstrated. The calculations show a satisfactory agreement with available experimental data, except for the recent NRF measurements of M. Tamkas et al for $M 1$ strength at 4-6 MeV, where, in contradiction with our calculations and previous $(p, p^{'})$ data, almost no $M 1$ strength was observed.
nucl-thEPJA(2024)·1 citation
04
Fine structure of the isoscalar giant monopole resonance in $^{58}$ Ni, $^{90}$ Zr, $^{120}$ Sn and $^{208}$ Pb
A. Bahini🇿🇦 · P. von Neumann-Cosel🇩🇪 · J. Carter🇿🇦 · I. T. Usman🇿🇦 · N. N. Arsenyev🇷🇺 · A. P. Severyukhin🇷🇺 · E. Litvinova🇺🇸 · R. W. Fearick🇿🇦 · R. Neveling🇿🇦 · P. Adsley🇿🇦 · N. Botha🇿🇦 · J. W. Brümmer🇿🇦 and 17 other authors
Over the past two decades high energy-resolution inelastic proton scattering studies were used to gain an understanding of the origin of fine structure observed in the isoscalar giant quadrupole resonance (ISGQR) and the isovector giant dipole resonance (IVGDR). Recently, the isoscalar giant monopole resonance (ISGMR) in $^{58}$ Ni, $^{90}$ Zr, $^{120}$ Sn and $^{208}$ Pb was studied at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) by means of inelastic $α$ -particle scattering at very forward scattering angles (including $0 \circ$ ). The good energy resolution of the measurement revealed significant fine structure of the ISGMR.~To extract scales by means of wavelet analysis characterizing the observed fine structure of the ISGMR in order to investigate the role of different mechanisms contributing to its decay width. Characteristic energy scales are extracted from the fine structure using continuous wavelet transforms. The experimental energy scales are compared to different theoretical approaches performed in the framework of quasiparticle random phase approximation (QRPA) and beyond-QRPA including complex configurations using both non-relativistic and relativistic density functional theory. All models highlight the role of Landau fragmentation for the damping of the ISGMR especially in the medium-mass region. Models which include the coupling between one particle-one hole (1p-1h) and two particle-two hole (2p-2h) configurations modify the strength distributions and wavelet scales indicating the importance of the spreading width. The effect becomes more pronounced with increasing mass number. Wavelet scales remain a sensitive measure of the interplay between Landau fragmentation and the spreading width in the description of the fine structure of giant resonances.
↳ nucl-exnucl-thPRC(2024)·10 citations
05
Artificial first-order phase transition in a magnetized Nambu--Jona-Lasinio model with a quark anomalous magnetic moment
William R. Tavares🇧🇷 · Sidney S. Avancini🇧🇷 · Ricardo L. S. Farias🇧🇷 · Rafael P. Cardoso🇧🇷
Recently, first-order phase transitions have been predicted as an effect of the inclusion of quark anomalous magnetic moment (AMM) in the hot and magnetized Nambu--Jona-Lasinio model (NJL). These transitions appear in the chiral condensate for different combinations of AMM and magnetic fields and could lead to inverse magnetic catalysis. However, in this work, we show that the predicted first-order phase transitions are related to regularization-dependent issues. To show this, we explore, in the context of the vacuum magnetic regularization (VMR) scheme, two different scenarios: when mass-dependent (MD) and mass-independent (MI) terms are present in the subtraction of the divergences. In the MD case, as we increase the AMM value, it is observed the appearance of a nonmassive minimum in the thermodynamical potential, which induces a first-order phase transition from the massive minimum. We argue that the MD terms must be avoided in order to satisfy the predictions of Lattice QCD, and we propose a MI solution that is valid in the limit which the magnetic fields are smaller than the squared of vacuum effective quark mass.
↳ hep-phhep-lathep-thnucl-thPRD(2024)·13 citations
06
The three channels of many-body perturbation theory: $G W$ , particle-particle, and electron-hole $T$ -matrix self-energies
Roberto Orlando · Pina Romaniello · Pierre-François Loos
We derive the explicit expression of the three self-energies that one encounters in many-body perturbation theory: the well-known $G W$ self-energy, as well as the particle-particle and electron-hole $T$ -matrix self-energies. Each of these can be easily computed via the eigenvalues and eigenvectors of a different random-phase approximation (RPA) linear eigenvalue problem that completely defines their corresponding response function. For illustrative and comparative purposes, we report the principal ionization potentials of a set of small molecules computed at each level of theory. The performance of these schemes on strongly correlated systems (\ce{B2} and \ce{C2}) is also discussed.
↳ physics.chem-phcond-mat.mtrl-scicond-mat.str-elnucl-thJ.Chem.Phys.(2023)·5 citations
07
Small systems and the single-hit approximation in the AMY parton cascade ALPACA
Robin Törnkvist🇸🇪 · Korinna Zapp🇸🇪
Understanding how momentum anisotropies arise in small collision systems is important for a quantitative understanding of collectivity in terms of QCD dynamics in small and large collision systems. In this letter we present results for small collision systems from the newly developed parton cascade \textsc{Alpaca}, which faithfully encodes the AMY effective kinetic theory. \textsc{Alpaca} reproduces quantitatively previously know results from a calculation in the single-hit approximation for small values of the coupling. We discuss in detail how such a comparison is to be carried out. Particularly at larger coupling a generic differences between the two approaches becomes apparent, namely that in parton cascades particles interact over a finite distance while in direct integrations of the Boltzmann equation the interactions are local. This leads to quantitative differences in the extracted values for the elliptic flow coefficient. These discrepancies appear in situations where the mean free path is not large compared to the interaction time and the applicability of kinetic theory is thus questionable.
↳ hep-phnucl-thPLB(2024)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE

Efimov states in excited nuclear halos

Microscopic optical potentials for medium-mass isotopes derived at the first order of the Watson multiple scattering theory

Microscopic analysis of dipole electric and magnetic strengths in 156Gd

Fine structure of the isoscalar giant monopole resonance in 58Ni, 90Zr, 120Sn and 208Pb

Artificial first-order phase transition in a magnetized Nambu--Jona-Lasinio model with a quark anomalous magnetic moment

The three channels of many-body perturbation theory: GW, particle-particle, and electron-hole T-matrix self-energies

Small systems and the single-hit approximation in the AMY parton cascade ALPACA

Affiliations

Microscopic analysis of dipole electric and magnetic strengths in $^{156}$ Gd

Fine structure of the isoscalar giant monopole resonance in $^{58}$ Ni, $^{90}$ Zr, $^{120}$ Sn and $^{208}$ Pb

The three channels of many-body perturbation theory: $G W$ , particle-particle, and electron-hole $T$ -matrix self-energies