Few-Body Systems最新文献

We study the reaction mechanism of (phi )-meson photoproduction on the nucleon and ({}^4)He targets by using a dynamical model based on a Hamiltonian. In addition to the dominant contribution of the Pomeron exchange, various meson exchanges are considered in the t channel to describe the CLAS data in the low energy region ({sqrt{s}} = (1.97 - 2.84)) GeV. The direct (phi ) radiations are taken into account in the s- and u-channels. The backward structures at ({sqrt{s}} approx 2.1) and 2.3 GeV are well reproduced by the inclusion of the s-channel (N(2000,5/2^+)) and (N(2300,1/2^+)) resonances, respectively. We also consider the final (phi N) interactions by the gluon exchange, the direct (phi N) interactions, and the box diagrams arising from the couplings with the (pi N), (rho N), (K Lambda ), and (K Sigma ) channels. The effects of the final state interactions are found to be very weak. Then the resulting Hamiltonian is used to study the coherent (gamma {}^4{textrm{He}} rightarrow phi {}^4{textrm{He}}) reaction within the distorted-weave impulse approximation. The calculated differential cross sections account for the LEPS data quite well.

Many-body forces, and specially three-body forces, are sometimes a relevant ingredient in various fields, such as atomic, nuclear or hadronic physics. As their precise structure is generally difficult to uncover or to implement, phenomenological effective forces are often used in practice. A form commonly used for a many-body variable is the square-root of the sum of two-body variables. Even in this case, the problem can be very difficult to treat numerically. But this kind of many-body forces can be handled at the same level of difficulty than two-body forces by the envelope theory. The envelope theory is a very efficient technique to compute approximate, but reliable, solutions of many-body systems, specially for identical particles. The quality of this technique is tested here for various three-body forces with non-relativistic systems composed of three identical particles. The energies, the eigenfunctions, and some observables are compared with the corresponding accurate results computed with a numerical variational method.

The stability of trapped bosons with repulsive interaction is studied using an approximate many-body calculation. Instead of using the traditional harmonic trapping potential we consider an anharmonic potential of the form (V_{anhar}(r)=frac{1}{2}momega ^{2}r^{2}+lambda r^{4}). In our method, a correlated two-body basis function is used which considers all two-body correlations. It is explained that negative value of anharmonic parameter ((lambda )) are capable to change a stable condensate into a metastable one. Within this metastable condensate, we slowly increase the number of atom (A) and find a collapsing nature of repulsive condensate. The process of collapse of repulsive Bose–Einstein condensation (BEC) is completely different from the collapsing process of attractive BEC and it is explained in details. A dramatic behaviour of interaction energy, kinetic energy, trapping potential energy along with the total ground state energy of this metastable repulsive BEC is observed. We also study the instability of these zero point energies by varying (lambda ) when fixed number of bosons are trapped by the anharmonic well and find critical values of (lambda ) at which the system collapses. When the number of trapped particle is sufficiently high, a close interplay between number of particle and anharmonic strength is observed to remodel the shape of the effective metastable region.

In this work, we investigate the solutions of the two-dimensional Duffin–Kemmer–Petiau oscillator for spin-one particles under a minimal length assumption. To incorporate the minimal length, we assume a generalized uncertainty principle with two deformation parameters implying a noncommutative phase space. By employing the momentum representation, we were able to solve the problem exactly for all spin projection numbers and obtain the minimal length corrections brought to the energy eigenvalues and the associated eigenstates of the oscillator. The solutions are systematically classified into natural and unnatural parity states contingent upon the spin-projection numbers. Additionally, we studied the effect of applying an external transverse homogeneous magnetic field (HMF) on the dynamics of the system. In particular, the motion of a spin-one boson moving in the plane under a HMF is considered as a special case. We also discuss the nonrelativistic limit of the energy eigenvalues in each one of the considered instances.

We calculate the (^{11})B((n,gamma )^{12})B reaction rate which is an important constituent in nucleosynthesis networks and is contributed by resonant as well as non-resonant capture. For the resonant rate, we use the narrow resonance approximation whereas the non-resonant contribution is calculated with the Coulomb dissociation method for which we use finite-range distorted wave Born approximation theory. We then compare our calculated rate of (^{11})B((n,gamma )^{12})B reaction with those reported earlier and with other charged particle reactions on (^{11})B.

A pseudochannel extension of the coupled-reaction-channel (CRC) ansatz had been used in earlier work to simulate the effect of the breakup channel on the rearrangement amplitudes. Comparisons with benchmark results on model systems established that rearrangement amplitudes and total breakup probability could be obtained accurately. However, achieving the same level of accuracy with respect to the state-to-state breakup amplitudes had eluded the earlier attempts that used global bases to generate the pseudo states. With the global bases it is difficult to control the spectrum of pseudostate energies and to obtain an optimal distribution of these pseudo-levels. In the present work, local bases in momentum space of the type used in Finite Element methods are employed. Pseudostates are generated using a local interpolation basis in the relative momentum of the two-body subsystem. Local nature of such a basis allows us to control the density of two-body pseudostates by simply adjusting the distribution of the grid points. In the present work, it is demonstrated that breakup amplitudes can be extracted quantitatively using pseudostates generated from a basis of local piecewise quadratic interpolation polynomials. For a local-potential s-wave model of the (textrm{n}+textrm{d}) scattering, state-to-state breakup amplitudes obtained from the present approach are compared with the benchmark results available in the literature. Results further confirm that pseudostate-extended CRC method is a viable and efficient approach for three-particle scattering.

This study presents a novel many-channel microscopic model to describe high-energy resonance states in (^9)Be and (^9)B, particularly addressing the cosmological lithium problem. The model integrates multiple three-cluster configurations and binary channels, unveiling 18 resonance states in each nucleus. Significant emphasis is placed on understanding resonance states’ impact on astrophysical S-factors, particularly in reactions involving (^7)Li, (^7)Be, (^6)Li, (^3)H, (^3)He and a deuteron. The results highlight the influence of resonance states and channel coupling on S-factors, offering new insights into nuclear reactions crucial for cosmological inquiries. This comprehensive analysis bridges theoretical predictions with experimental data, enhancing our understanding of nuclear processes in astrophysical contexts.

Dynamical vortex production and quantum turbulence emerging in periodic perturbed quasi-two-dimensional (q2D) Bose–Einstein condensates are reported by considering two distinct time-dependent approaches. In both cases, dynamical simulations were performed by solving the corresponding 2D mean-field Gross-Pitaevskii formalism. (1) In the first model, a binary mass-imbalanced system is slightly perturbed by a stirring time-dependent elliptic external potential. (2) In the second model, for single dipolar species confined in q2D geometry, a circularly moving external Gaussian-shaped obstacle is applied in the condensate, at a fixed radial position and constant rotational speed, enough for the production of vortex–antivortex pairs. Within the first case, vortex patterns are crystalized after enough longer period, whereas in the second case, the vortex pairs remains interacting dynamically inside the fluid. In both cases, the characteristic Kolmogorov spectral scaling law for turbulence can be observed at some short time interval.

Coupling of orbital motion to a spin degree of freedom gives rise to various transport phenomena in quantum systems that are beyond the standard paradigms of classical physics. Here, we discuss features of spin-orbit dynamics that can be visualized using a classical model with two coupled angular degrees of freedom. Specifically, we demonstrate classical ‘spin’ filtering through our model and show that the interplay between angular degrees of freedom and dissipation can lead to asymmetric ‘spin’ transport.

Theoretically, in (1 + 1) dimensions, one can have Klein–Fock–Gordon–Majorana (KFGM) particles. More precisely, these are one-dimensional (1D) Klein–Fock–Gordon (KFG) and Majorana particles at the same time. In principle, the wave equations considered to describe such first-quantized particles are the standard 1D KFG equation and/or the 1D Feshbach–Villars (FV) equation, each with a real Lorentz scalar potential and some kind of Majorana condition. The aim of this paper is to analyze the latter assumption fully and systematically; additionally, we introduce specific equations and boundary conditions to characterize these particles when they lie within an interval (or on a line with a tiny hole at a point). In fact, we write first-order equations in the time derivative that do not have a Hamiltonian form. We may refer to these equations as first-order 1D Majorana equations for 1D KFGM particles. Moreover, each of them leads to a second-order equation in time that becomes the standard 1D KFG equation when the scalar potential is independent of time. Additionally, we examine the nonrelativistic limit of one of the first-order 1D Majorana equations.