Nuclear Theory·nucl-th

Thursday·August 22, 2024

8 papers—3 primary·5 cross-listed

01
Semiclassical Features of Wobbling and Chiral Properties in Nuclei
Apolodor Aristotel Raduta · Cristian Mircea Raduta · Robert Poenaru
A semiclassical approach is used to describe the wobbling and chiral motion in even-even and odd-even nuclei The trial function involved in the variational equation for the quantal action is a coherent state for the SU(2 ) group associated to a triaxial rotor for the case of an even-even system and a coherent state for the group SU(2) $\otimes$ SU(2) describing the particle-core system. Application is made for $^{158}$ Er and $^{161, 163, 165, 167}$ Lu, $135$ Pr. Th parameters involved in the coherent state expression are complex numbers depending on time and play the role of the phase space generalized conjugate coordinates whose equation of motion may be brought to the Hamilton canonical form.Within a harmonic approximation one analytically obtains the wobbling frequencies which are further used to calculate the excitation energies for the states forming a band. A new procedure to quantize the classical orbitals is proposed. In the new picture the electromagnetic transition probabilities are calculated both for the in-band and the intraband transitions. Additionally, for odd systems, some other observable like aligned angular momentum, excitation energies relative to a reference spectrum, dynamic moment of energies are calculated and compared with the corresponding experimental data.In the parameter space one identified several nuclear phases with specific properties. An example is given where the wobbling and chiral motions coexist. The existence of a transversal wobbling is widely commented. A new boson representation for the angular momenta is proposed. The approach was successfully applied to $^{135}$ Pr. One concludes that semiclassical description is an efficient tool to account quantitatively for the wobbling and chiral properties in nuclei.
nucl-th0 citations
02
Role of momentum in the generator-coordinate method applied to barrier penetration
K. Hagino · G.F. Bertsch
Nuclear fission at barrier-top energies is conventionally modeled by a one-dimensional Schrödinger equation applied to internal fission channels, but that treatment is hard to justify in the configuration-interaction approach to nuclear Hamiltonians. Here we show that inclusion of states of finite momentum by the Generator Coordinate Method (GCM) considerably extends the range of energies at which GCM-based Hamiltonians could reproduce the Schrödinger treatment. The transmission probabilities for crossing the barrier are calculated by a discrete version of Kohn's variational method, which may also be useful for other systems of interacting fermions.
nucl-thphysics.atom-phphysics.chem-phquant-phPRC(2024)·5 citations
03
Capture Rates of Highly Degenerate Neutrons
B. Knight · O. L. Caballero · H. Schatz
At the low temperature and high density conditions of a neutron star crust neutrons are degenerate. In this work, we study the effect of this degeneracy on the capture rates of neutrons on neutron rich nuclei in accreted crusts. We use a statistical Hauser-Feshbach model to calculate neutron capture rates and find that neutron degeneracy can increase rates significantly. Changes increase from a factor of a few to many orders of magnitude near the neutron drip line. We also quantify uncertainties due to model inputs for masses, $γ$ -strength functions, and level densities. We find that uncertainties increase dramatically away from stability and that degeneracy tends to increase these uncertainties further, except for cases near the neutron drip line where degeneracy leads to more robustness. As in the case of capture of classically distributed neutrons, variations in the mass model have the strongest impact. Corresponding variations in the reaction rates can be as high as 3 to 4 orders of magnitude, and be more than 5 times larger than under classical conditions. To ease the incorporation of neutron degeneracy in nucleosynthesis networks, we provide tabulated results of capture rates as well as analytical expressions as function of temperature and neutron chemical potential, for proton numbers between $3 \leq Z \leq 85$ , derived from fits to our numerical results. Fits are based on a new parametrization that complements previously employed power law approximations with additional Lorentzian terms that account for low energy resonances, significantly improving accuracy.
nucl-thastro-ph.HEJ.Phys.G(2024)·2 citations
04
Towards a first principles light-front Hamiltonian for the nucleon
Siqi Xu🇨🇳 · Yiping Liu🇨🇳 · Chandan Mondal🇨🇳 · Jiangshan Lan🇨🇳 · Xingbo Zhao🇨🇳 · Yang Li🇨🇳 · James P. Vary🇺🇸
We solve the nucleon's wave functions from the eigenstates of the light-front quantum chromodynamics Hamiltonian for the first time, using a fully relativistic and nonperturbative approach based on light-front quantization, without an explicit confining potential. These eigenstates are determined for the three-quark, three-quark-gluon, and three-quark-quark-antiquark Fock representations, making them suitable for low-resolution probes. From this, we calculate the nucleon's quark and gluon matter densities, helicity, and transversity distributions, which show qualitative consistency with experimental extractions. We also compute the contributions of quark and gluon helicity to the proton spin and the tensor charges. The obtained light-front wave functions represent a significant advancement towards a unified description of various hadron distribution functions in both longitudinal and transverse momentum space.
↳ hep-phnucl-thPLB(2025)·24 citations
05
Photoproduction $γ p \to f_{0} (980) p$ in an effective Lagrangian approach
Neng-Chang Wei🇨🇳 · Ai-Chao Wang🇨🇳 · Fei Huang🇨🇳
The most recent data on differential cross sections and photon beam asymmetries $Σ$ from the LEPS2/BGOegg Collaboration for the $γ p \to f_{0} (980) p$ reaction are analyzed within a tree-level effective Lagrangian approach. The $t$ -channel $ρ$ and $ω$ exchanges, the $u$ - and $s$ -channel $N$ exchanges, the interaction current, and the possible $s$ -channel $N^{*}$ exchanges are taken into account in constructing the reaction amplitudes to reproduce the data. The results show that the contributions from either the $N (2040) 3/ 2^{+}$ or the $N (2100) 1/ 2^{+}$ resonance exchange in the $s$ channel are necessarily required to describe the LEPS2/BGOegg data and they dominate the differential cross sections of $γ p \to f_{0} (980) p$ . Further analysis shows that the contributions from the $t$ -channel $ρ$ and $ω$ exchanges and the interaction current are rather small to both differential cross sections and photo beam asymmetries, and the contributions from $u$ -channel $N$ exchange are considerable in the case of including $N (2040) 3/ 2^{+}$ in the model while negligible in the case of including $N (2100) 1/ 2^{+}$ in the model. Predictions of target asymmetries $T$ for $γ p \to f_{0} (980) p$ are given, which can be examined by future experiments.
↳ hep-phnucl-thPRC(2024)·4 citations
06
Second-order spin hydrodynamics from Zubarev's nonequilibrium statistical operator formalism
Abhishek Tiwari🇮🇳 · Binoy Krishna Patra🇮🇳
Using the Zubarev's nonequilibrium statistical operator formalism, we derive the second-order expression for the dissipative tensors in relativistic spin hydrodynamics, {\em viz.} rotational stress tensor ( $τ_{μν}$ ), boost heat vector ( $q_{μ}$ ), shear stress tensor ( $π_{μν}$ ), and bulk viscous pressure ( $Π$ ). The first two ( $τ_{μν}$ and $q_{μ}$ ) emerge due to the inclusion of the antisymmetric part in the energy-momentum tensor, which, in turn, governs the conservation of spin angular momentum ( $Σ^{α μν}$ ). As a result, new thermodynamic forces, generated due to the antisymmetric part of $T_{μν}$ , contain the spin chemical potential. In this work, we have also taken the spin density ( $S^{μν}$ ) as an independent thermodynamic variable, in addition to the energy density and particle density, thereby resulting in two novel transport coefficients given by the correlation between spin density tensor and rotational stress tensor and vice versa. Additionally, the newly found terms in $π_{μν}$ and $Π$ are the artifacts of the new thermodynamic forces that arise due to the antisymmetric part of $T^{μν}$ . Finally, we have derived the evolution equations for the aforesaid tensors: $τ_{μν}$ , $q_{μ}$ , $π_{μν}$ , and $Π$ .
↳ hep-thhep-phnucl-thPRD(2025)·19 citations
07
Strong decays of $P -$ wave doubly charmed and bottom baryons
Ya-Li Shu🇨🇳 · Qing-Fu Song🇨🇳 · Qi-Fang Lü🇨🇳
In this work, we investigate the strong decays for $P -$ wave excited states of doubly charmed and bottom baryons in the constituent quark model. Our results indicate that some $λ -$ mode $Ξ_{cc / bb} (1 P)$ and $Ω_{cc / bb} (1 P)$ states are relatively narrow, which are very likely to be discovered by future experiments. The light meson emissions for the low-lying $ρ -$ mode states are highly suppressed due to the orthogonality of wave functions between initial and final states. Moreover, the strong decay behaviors for doubly charmed and bottom baryons preserve the heavy superflavor symmetry well, where the small violation originates from the finite heavy quark masses and different phase spaces. We hope that present theoretical results for undiscovered doubly charmed and bottom baryons can provide helpful information for future experiments and help us to better understand the heavy quark symmetry.
↳ hep-phhep-exnucl-thCommun.Theor.Phys.(2026)·3 citations
08
How the QCD trace anomaly behaves at the core of twin stars?
José C. Jiménez🇧🇷 · Lucas Lazzari🇧🇷 · Victor P. Gonçalves🇧🇷
We investigate the behavior of the dense and cold (normalized) QCD trace anomaly, $Δ$ , in the interior of twin neutron stars (obtained from several sets of equations of state in agreement with modern compact-star and multimessenger data) satisfying static and dynamic stability conditions. We scan the formed twin-star parameter space in order to look for effects caused by the presence of a strong first-order phase transition connecting hadron and quark phases by means of a Maxwell construction. We found robustly that $Δ$ suffers an abrupt decrease around the transition point, even reaching large negative values ( $Δ ≃ - 0.35$ ), in marked contrast to current studies pointing out a smooth behavior with $Δ ≳ 0$ at all densities. Besides, we characterize the behavior of {the recently defined} conformal factor, $d_{c}$ , in our four categories of twin stars for which we perform comparisons with theoretical constraints put, e.g. by Bayesian studies sometimes adjusted to agree with perturbative QCD at high densities. These analyses allow us to hypothesize modifications in the strong QCD coupling in dense nuclear matter with a strong thermodynamic discontinuity.
↳ hep-phgr-qchep-latnucl-thPRD(2024)·22 citations

Affiliations

first authorsco-authorsvia INSPIRE