Nuclear Theory·nucl-th

Friday·January 6, 2023

6 papers—5 primary·1 cross-listed

01
Cluster-shell competition and effect of adding hyperons
Naoyuki Itagaki · Emiko Hiyama
The fundamental question is how the hyperon plays a role in the nuclear structure. It is of particular importance, especially in the light mass region, to verify the structure change when $Λ$ particle(s) is added to normal nuclei. The ground state of $^{8}$ Be has been know to have a well-developed $α$ -- $α$ cluster structure, whereasn $^{12}$ C has a mixed structure of three $α$ clusters and $j j$ -coupling shell model, where $α$ clusters are partially broken. Adding $Λ$ particle(s) could induce the structure change. We compare the Be and C cases. Using the antisymmetrized quasi-cluster model (AQCM), the $α$ -cluster states and $j j$ -coupling shell-model states of $^{8}$ Be and $^{12}$ C are prepared on the same footing, and we add $Λ$ particles. The cluster-shell competition in the ground state can be well described with this model. Using AQCM, we calculate $^{8}$ Be, $_{Λ}^{9}$ Be, $_{ΛΛ}^{10}$ Be, $^{12}$ C, $_{Λ}^{13}$ C, and $_{ΛΛ}^{14}$ C. By adding one or two $Λ$ particle(s), the ground state of $^{12}$ C approaches the $j j$ -coupling shell model side. On the other hand, in the Be case, although the $Λ$ particle(s) shrinks the $α$ -- $α$ distance, the breaking effect of the cluster structure is rather limited. The spin-orbit interaction is the driving force of breaking the $α$ clusters, and whether the glue-like effect of $Λ$ particle(s) attracts the cluster inside the range of this interaction is crucial. In $_{ΛΛ}^{14}$ C, the breaking of $α$ clusters in $^{12}$ C is much enhanced by the addition of the $Λ$ particles than the case of free $^{12}$ C. We also found that breaking $α$ clusters in the ground state of $_{ΛΛ}^{14}$ C affects the excited state with the pure cluster structure.
nucl-thnucl-exPRC(2023)·4 citations
02
Ab initio descriptions of $A = 16$ mirror nuclei with resonance and continuum coupling
S. Zhang · F. R. Xu · J. G. Li · B. S. Hu · Z. H. Cheng · N. Michel · Y. Z. Ma · Q. Yuan · Y. H. Zhang
We have used an {\it ab initio} Gamow shell model to study the isospin symmetry breaking in the $A = 16$ mirror nuclei of $^{16}$ F, $^{16}$ N, $^{16}$ Ne and $^{16}$ C. Starting from a chiral interaction with two-nucleon force (2NF) at N $^{3}$ LO and three-nucleon force (3NF) at N $^{2}$ LO, a complex-momentum $psd$ -shell Hamiltonian was constructed by employing the many-body perturbation theory in the Gamow Hartree-Fock basis which includes bound, resonant and continuum states self-consistently. Such an elaborated {\it ab initio} Gamow shell model with both continuum coupling and 3NF included can properly treat the many-body correlations of weakly bound and unbound nuclei. The mirror partners of $^{16}$ F and $^{16}$ N exhibit different level orders in their excitation spectra, which can be well explained by the inclusion of 3NF in the calculation. The isospin asymmetry between the mirror partners $^{16}$ Ne and $^{16}$ C was studied in detail by insight into their configuration structures. The interplay between 3NF and the continuum coupling is discussed in the weakly bound and unbound nuclear states.
nucl-thPRC(2023)·18 citations
03
$0^{+}$ to $2^{+}$ neutrinoless double- $β$ decay of $^{76}$ Ge, $^{82}$ Se, $^{130}$ Te and $^{136}$ Xe in the microscopic interacting boson model}
J. Ferretti🇫🇮 · R. Magana Vsevolodovna🇮🇹 · J. Kotila🇫🇮 · E. Santopinto🇮🇹
Here, we study the neutrinoless double- $β$ ( $0 ν β β$ ) decay between the ground state and the first $2^{+}$ state of $^{76} \mbox G e \to^{76} \mbox S e$ , $^{82} \mbox S e \to^{82} \mbox K r$ , $^{130} \mbox T e \to^{130} \mbox X e$ and $^{136} \mbox X e \to^{136} \mbox B a$ systems. The relevant nuclear matrix elements (NMEs) involved in the process are calculated within the formalism of the microscopic interacting boson model (IBM-2). The IBM-2 has been widely used to obtain predictions for nuclear observables, such as the spectrum, but also to explore the possible emergence of beyond-the-Standard Model effects in the weak interactions of nuclei. Our calculations are carried out by considering the exchange of a Majorana neutrino between two nucleons ( $2 N$ -mechanism). In addition to NMEs, we calculate the associated leptonic phase-space factors (PSFs) using electron radial wave functions, which are obtained by solving numerically the Dirac equation of a screened Coulomb potential that takes into account finite nuclear size. By combining our IBM-2 results for the NMEs with those for the PSFs along with experimental half-life limits, we can set limits on the $⟨ λ ⟩$ and $⟨ η ⟩$ couplings of left-right (L-R) models.
nucl-thhep-ph2 citations
04
Topology and emergent symmetries in dense compact star matter
Yong-Liang Ma🇨🇳 · Wen-Cong Yang🇨🇳
It has been found that the topology effect and the possible emergent scale and hidden local flavor symmetries at high density reveal a novel structure of the compact star matter. The $N_{f} \geq 2$ baryons can be described by the skyrmion in the large $N_{c}$ limit and there is a robust topology change in the skyrmion matter approach to dense nuclear matter. The hidden scale and local flavor symmetries which are sources introducing the lightest scalar meson -- dilaton -- and lowest lying vector mesons into to nonlinear chiral effective theory are seen to play important roles in understanding the nuclear force. We review in this paper the generalized nuclear effective theory (G $n$ EFT), which applicable to nuclear matter from low density to the compact star density, constructed with the robust conclusion from the topology approach to dense matter and emergent scale and hidden local flavor symmetries. The topology change at density larger than two times saturation density $n_{0}$ encoded in the parameters of the effective field theory is interpreted as the hadron-quark continuity in the sense of Cheshire Cat Principle. A novel feature predicted in this theory that has not been found before is the precocious appearance of the conformal sound velocity in the cores of massive stars, although the trace of the energy-momentum tensor of the system is not zero. That is, in contrast to the usual picture, the cores of massive stars are composed of quasiparticles of fractional baryon charges, neither baryons nor deconfined quarks. Hidden scale and local flavor symmetries emerge and give rise a resolution of the longstanding $g_{A}$ quench problem in nuclei transition. To illustrate the rationality of the GnEFT, we finally confront the generalized effective field theory to the global properties of neutron star and the data from gravitational wave detections.
nucl-thhep-phSymmetry(2023)·14 citations
05
Reduced nuclear helicity amplitudes for deuteron electrodisintegration and other processes
J. Flores🇺🇸 · S.S. Chabysheva🇺🇸 · J.R. Hiller🇺🇸
We extend the original idea of reduced nuclear amplitudes to capture individual helicity amplitudes and discuss various applications to exclusive processes involving the deuteron. Specifically, we consider deuteron form factors, structure functions, tensor polarization observables, photodisintegration, and electrodisintegration. The basic premise is that nuclear processes at high momentum transfer can be approximated by tree graphs for point-like nucleons supplemented by empirical form factors for each nucleon. The latter represent the internal structure of the nucleon, and incorporate nonperturbative physics, which can allow for early onset of scaling behavior. The nucleon form factors are evaluated at the net momentum transfer experienced by the given nucleon, with use of $G_{E}$ for a no-flip contribution and $G_{M}$ for a helicity-flip contribution. Results are compared with data where available. The deuteron photodisintegration asymmetry $Σ$ is obtained with a value of $Σ (9 0^{\circ}) ≃ - 0.06$ , which is much closer to experiment than the value of -1 originally expected. The method also provides an estimate of the momentum transfer values required for scaling onset. We find that the deuteron structure function $B$ is a good place to look, above momentum transfers of 10 GeV $^{2}$ .
nucl-thhep-phPRC(2023)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE

Cluster-shell competition and effect of adding hyperons

Ab initio descriptions of A=16 mirror nuclei with resonance and continuum coupling

0+ to 2+ neutrinoless double-β decay of 76Ge, 82Se, 130Te and 136Xe in the microscopic interacting boson model}

Topology and emergent symmetries in dense compact star matter

Reduced nuclear helicity amplitudes for deuteron electrodisintegration and other processes

Affiliations

Ab initio descriptions of $A = 16$ mirror nuclei with resonance and continuum coupling

$0^{+}$ to $2^{+}$ neutrinoless double- $β$ decay of $^{76}$ Ge, $^{82}$ Se, $^{130}$ Te and $^{136}$ Xe in the microscopic interacting boson model}