Few-Body Systems最新文献

We discuss the problem of determining the strengths of short-range components in a chiral three-nucleon force (3NF) by comparing theoretical predictions with nucleon-deuteron (Nd) scattering data. A perturbative treatment of contact terms when solving the three-nucleon (3N) continuum Faddeev equation seems to be particularly well suited to dealing with variable strengths of such components in the chiral 3NF. A significant reduction of the computation time achieved in this way makes such an approach a valuable tool for fine-tuning of the 3N Hamiltonian parameters.

The impact of the dense quantum plasma on the bound (1sns; (^1)S(^e)) [(n=1-5)] and a few low-lying doubly excited resonance (2sns, 2pnp; (^1)S(^e)) [(n=2-3)] states of various two-electron highly charged He-like C(^{4+}), Mg(^{10+}), Al(^{11+}), Si(^{12+}), S(^{14+}) and Ar(^{16+}) ions has been studied using an explicitly correlated multi-exponent Hylleraas type basis set under the framework of Ritz variational method. Utilizing the state-of-art stabilization technique, the bound states properties and the resonance parameters (energy and width) are determined under different plasma conditions. Ionization potential depression with respect to the plasma screening length is rigorously investigated for both the bound and resonance states. The width (or the lifetime) of the resonance states originating from different electronic configurations follows unique patterns with respect to the plasma screening length. Most of the data for the resonance parameters are being reported here for the first time in the literature.

In this work we study spin-0 particles described by the Klein-Gordon oscillator formalism in a spacetime which structure is determined by a homogeneous magnetic field and a cosmological constant. For this purpose we take into account a framework based on the Bonnor-Melvin solution with the inclusion of the cosmological constant. We write and solve the Klein-Gordon equation, and then find the energy spectrum by considering the effect of vector and scalar potentials.

This paper reviews our work on the measurements of absolute production cross sections of (gamma )-rays from the (p,p(^{prime }gamma )) reactions on (^{12})C and (^{16})O. The measurements cover a range of 8–16 MeV for the incident proton beam. The angular distributions of the (gamma )-rays have been measured. A detailed phenomenological analysis within the framework of optical model formalism has been carried out to reproduce the experimental data. The existing global set of elastic, polarization and total reaction data for protons and neutrons have been used to generate the optical model potential. The nuclear structure effects have been included in the calculations by considering the roles of coupling of the low-lying states, the presence of resonances and nuclear deformations. The potentials so generated have been used to calculate the differential and total cross sections for both (p,p(^prime )) and (p,p(^prime gamma )) reactions. The results of the analysis are in good agreement with the measured data for the observed (gamma )-rays. However, discrepancies still exist in reproducing the finer details of the cross sections. The existing discrepancies between our phenomenological analysis and the experimental data demonstrate the rather complex roles of channel couplings, resonances in the compound nuclear system and target deformation. The significant contribution of nuclear structure effects in light mass nucleus like (^{12})C and (^{16})O, leads to an apparent loss of predictive power of the theoretical calculation for low-energy region (less than 10 MeV) of the projectile energy.

We examine the results on the determination of the Coulomb-free ¹(S_0) proton–proton (p–p) scattering length by analyzing the cross section of the quasi-free p + d (rightarrow ) p + p + n reaction at center-of-mass energies below 1 MeV. This was achieved using a Bayesian data-fitting approach, yielding a p–p scattering length (a_{pp} = -18.17^{+0.52}_{-0.58}|_{stat}pm 0.01_{syst}) fm and effective range (r_0 = 2.80pm 0.05_{stat}pm 0.001_{syst}) fm. We test the stability of the results against the upper energy cutoff and fitting data sets separately. A model based on the Eckart potential is introduced for an effective description in the universal window. In this model, the short-range interaction is considered as a whole, similar to how the s-wave phase-shift (delta ) functions in describing low-energy nucleon–nucleon scattering data. Based on our analysis, we confirm that the obtained parameters accurately represent the characteristics of the short-range physics and the influence of the up-down quark mass difference on the charge symmetry breaking is less significant as initially anticipated. Additionally, we suggest evaluating the charge symmetry breaking of the short-range interaction rather than solely focusing on the nuclear interaction.

The coupling constants of (rho ) meson-nucleon and (omega ) meson-nucleon are connected through the isospin relation. Using the soft-wall model of holographic QCD, the current work aims to examine the violation (if any) of isospin symmetry of the (omega )-meson as well as the temperature dependency of the (omega )-meson-(Delta ) and (omega )-meson-nucleon-(Delta ) baryon coupling constants. Applying the temperature-dependent profile functions of the vector and fermion fields to the expression of the coupling constants in the model yields the temperature dependence of the coupling constants. The minimum and magnetic type interactions between vector and fermion fields in 5-dimensional AdS space-time are included in the written interaction Lagrangian terms. The temperature dependence of the coupling constants (g_{omega N N}(T)), (g_{omega Delta Delta }(T)), and (g_{omega N Delta }(T)) has been investigated. Comparing (g_{omega NN}(T)) with the coupling constant (g_{rho NN}(T)), it is found that the isospin symmetry of the (omega ) and (rho ) mesons is not violated at the finite temperature. It is also observed that the coupling constant of the (omega ) meson with baryons decreases as the temperature increases, and this coupling constant becomes zero near the confinement-deconfinement phase transition temperature.

The three-electron atomic-orbital close-coupling method is applied to H–He collision. The cross sections are calculated for projectile excitations to H(2 s) and H(2p), ionizations of projectile H, single ionization of target He, and electron capture for incident energy of 0.5–30 keV. Some basis sets are adopted to see the convergence behavior of the cross section for each process. The electron-exchange effect is essential to obtain reasonable results. Although the results have not yet reached convergence, the agreement with the experimental data is as good as previous calculations or better.

Using the folding procedure, we investigate the bound state of the (Omega )+(alpha ) system. Previous theoretical analyses have indicated the existence of a deeply bound ground state, which is attributed to the strong (Omega )-nucleon interaction. By employing well-established parameterizations of nucleon density within the alpha particle, we performed numerical calculations for the folding (Omega )-(alpha ) potential. Our results show that the (V_{Omega alpha }(r)) potential can be accurately fitted using a Woods-Saxon function, with a phenomenological parameter (R = 1.1A^{1/3} approx 1.74) fm ((A=4)) in the asymptotic region where (2< r < 3) fm. We provide a thorough description of the corresponding numerical procedure. Our evaluation of the binding energy of the (Omega )+(alpha ) system within the cluster model is consistent with both previous and recent reported findings. To further validate the folding procedure, we also calculated the (Xi )-(alpha ) folding potential based on a simulation of the ESC08c Y-N Nijmegen model. A comprehensive comparison between the (Xi )-(alpha ) folding and (Xi )-( alpha ) phenomenological potentials is presented and discussed.

We present the experimental apparatus enabling the observation of the heteronuclear Efimov effect in an optically trapped ultracold mixture of (^6)Li-(^{133})Cs with high-resolution control of the interactions. A compact double-species Zeeman slower consisting of four interleaving helical coils allows for a fast-switching between two optimized configurations for either Li or Cs and provides an efficient sequential loading into their respective MOTs. By means of a bichromatic optical trapping scheme based on species-selective trapping we prepare mixtures down to 100 nK of ({1times 10^{4}}) Cs atoms and ({7times 10^{3}}) Li atoms. Highly stable magnetic fields allow high-resolution atom-loss spectroscopy and enable to resolve splitting in the loss feature of a few tens of milligauss. These features allowed for a detailed study of the Efimov effect.

Quantum few-body systems are deceptively simple. Indeed, with the notable exception of a few special cases, their associated Schrödinger equation cannot be solved analytically for more than two particles. One has to resort to approximation methods to tackle quantum few-body problems. In particular, variational methods have been proposed to ease numerical calculations and obtain precise solutions. One such method is the Stochastic Variational Method, which employs a stochastic search to determine the number and parameters of correlated Gaussian basis functions used to construct an ansatz of the wave function. Stochastic methods, however, face numerical and optimization challenges as the number of particles increases.We introduce a family of gradient variational methods that replace stochastic search with gradient optimization. We comparatively and empirically evaluate the performance of the baseline Stochastic Variational Method, several instances of the gradient variational method family, and some hybrid methods for selected few-body problems. We show that gradient and hybrid methods can be more efficient and effective than the Stochastic Variational Method. We discuss the role of singularities, oscillations, and gradient optimization strategies in the performance of the respective methods.