Toy model of the repulsive core of the nucleon-nucleon potential

We study the simplest quark model assuming that the sea of gluons and quark-antiquark pairs can be treated as a part of a static force and proceeding to calculate the hadronic states by solving the Schrödinger equation for a static confining interaction. We refer to this model, starting from a system of six interacting constituent quarks, and examine how the picture of two structureless nucleons can change when the effects caused by the substructure of the nucleons are taken into account.     

Gamow-Teller strength with realistic nucleon-nucleon interactions

Two realistic nucleon-nucleon interactions are used to calculate the energy-weighted sum rules for the Gamow-Teller operators. There are no free parameters in our calculations. The two interactions give similar results for ⁴⁸Ca and ⁹⁰Zr.     

Microscopic calculation of the repulsive core in the elastic nucleon-nucleon scattering

The resonating group method is used to study the effective potential between two nucleons, due to the confining potential between quarks taken together with the Pauli principle for quarks. The potential used has harmonic form, unitary spin factor λ(1)·λ(2), and both ordinary and spin-spin components. Its parameters are determined by appeal to experimental data, and phase shifts are calculated for the¹ S ₀ and³ S ₁ states of the nuncleon-nucleon (NN) system. The results indicate that the repulsive core in theNN potential may arise from quark antisymmetrization required if nucleons are composed of quarks.     

Shear viscosity of neutron matter from realistic nucleon-nucleon interactions

The calculation of transport properties of Fermi liquids, based on the formalism developed by Abrikosov and Khalatnikov, requires the knowledge of the probability of collisions between quasiparticles in the vicinity of the Fermi surface. We have carried out a study of the shear viscosity of pure neutron matter, whose value plays a pivotal role in determining the stability of rotating neutron stars, in which these processes are described using a state-of-the-art nucleon-nucleon potential. Medium modifications of the scattering cross section have been consistently taken into account through an effective interaction obtained from the matrix elements of the bare interaction between correlated states. Medium effects produce a large increase of the viscosity at densities rho > or approximately0.1 fm;{-3}.     

A nucleon-nucleon soft core central potential

We have calculated a central nucleon-nucleon potential with a soft core for the singleteven and the triplet-even state. The radial dependence of these potentials is given by a sum of one repulsive and two attractive Gaussians; therefore matrix elements with shell-model and cluster-model like functions may be calculated quite easily. The potentials are fitted to reproduce the phase shifts up to 300 MeV laboratory energy and the binding energy of the deuteron.     

Elastic scattering of heavy nuclei and nucleus-nucleus potential with repulsive core

The elastic scattering of ¹⁶O + ¹²C at various collision energies is discussed in the framework of the optical model with repulsive core nucleus-nucleus potential. The cross sections on backward angles are strongly raised due to repulsive core. It is shown by using the near-side/far-side decomposition method that the near-side component of the scattering amplitude mainly contributes to the elastic scattering cross sections on forward and backward angles. The repulsive core of ¹⁶O + ¹²C potential takes place at distances R ≲ 3 fm.     

The volume contribution of the ion-ion optical potential from realistic complex nucleon-nucleon interaction

The real and imaginary parts of the optical model potential for several pairs of magic nuclei have been calculated by a double folding procedure. The complex effective interaction is calculated from the Reid soft core potential by solving the Bethe-Goldstone equation in two colliding nuclear matters. The calculated potentials were approximated with a Woods-Saxon shape. We studied the dependence of the parameters of these Woods-Saxon forms on the masses of the interacting nuclei.     

Elastic scattering of heavy ions and nucleus-nucleus potential with a repulsive core

Elastic scattering of ¹²C + ¹²C at 139.5, 158.8 MeV and ¹⁶O + ¹²C at 132, 169 MeV was analyzed in the framework of an optical model using the repulsive-core nucleus-nucleus potential. Calculations with and without consideration of the core were performed and the influence of the core on the elastic scattering cross section was analyzed. It was shown that taking account of the core leads to an increase in the elastic scattering cross section for backward angles. The decomposition of the scattering amplitude into nearside and far-side components was studied.     

Phenomenology of the nucleon-nucleon potential

A local nucleon-nucleon potential expansion is developed in terms of orthogonal projectors. Considering the nucleon-nucleon (NN) potential as a completely phenomenological structure, the expansion provides an opportunity to obtain the NN scattering phase shifts that can be described by applying a restricted set of operators, dependent on angular and spin-isospin degrees of freedom of the interacting nucleons. The results obtained with an approximation for eight basic operators (central, spin-orbit and tensorial) are consistent with experience in the field, and provide directions for further modifications of realistic NN potentials.     

Study of a monomer-monomer reaction system with short-range repulsive interactions

The critical behavior of an interacting two species catalytic surface reaction model is studied by means of Monte Carlo simulations and a mean-field approach. The model has two parameters, namely the relative adsorption rate of species p _A and a short-range repulsive interaction r between the same type of adsorbed species. The system exhibits an stationary reactive phase and two symmetrically equivalent absorbing phases. These latter phases are unique and correspond to surfaces saturated by a single type of reacting species. For , the system exhibits a second-order phase transition that belongs to the directed percolation (DP) universality class. However, in the absence of repulsive interaction (r = 0), a bicritical point is found at p _A = 1/2 whose critical behavior is compatible with dynamical mean-field exponents. Our findings indicate that the bicritical point belongs to the Voter Model universality class, whose upper critical dimension is d _c = 2. In addition, we propose a method to study the crossover from MF to DP behavior based on the estimation of the crossover time T _c . We find that T _c diverges according to a power-law as where is the crossover exponent. For strong repulsion, a new transient effect appears associated with the onset of almost inactive chessboad patterns.Received: 8 July 2004, Published online: 31 August 2004PACS: 02.50.-r Probability theory, stochastic processes, and statistics - 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion - 82.45.Jn Surface structure, reactivity and catalysisR.A. Monetti: Permanent address: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, (INIFTA), CONICET, UNLP. Suc. 4, C. C. 16, (1900) La Plata, Argentina     

Interpretation of a repulsive core between fermion clusters

The notion of relative distance between two composite fermion clusters, such as nucleons in a quark model, is ambiguous at small separations. We examine the consequences of defining relative distance as the largest relative coordinate of all possible clusterings of the constituent particles. Such a definition can naturally yield a repulsive core in the effective potential between the two composite systems.     

Isosteric heat of adsorption for repulsive interactions

The isosteric heat of adsorption of particles with repulsive nearest-neighbour interactions on a square lattice is calculated using the transfer matrix method. A significant diminution of enhancement of this repulsion is observed around half-coverage and at temperatures below and near the order-disorder transition. Consequences for thermal desorption are examined.     

An analysis of BCS solutions with realistic interactions

We adopt the principle that the BCS solution can be regarded as a generating function for ground states of neighbouring nuclei. A parametrisation of the binding energy in terms of the number of particles is assumed and the assumption tested. Using an ansatz from statistical mechanics, a formula for the distribution of the number of particles is developed and the formula is shown to give accurate answers. The concept of temperature is introduced and its interpretation in many-particle theory is clarified.     

具有排斥相互作用的原子团簇非平衡系统研究

在无格点基底表面建立了存在排斥相互作用的原子团簇凝聚及扩散模型，对沉积在均匀带电硅油基底表面的银原子凝聚过程进行了研究.结果表明：当沉积原子凝聚成稳定的原子团簇后，由于带同种电荷，团簇之间存在库仑排斥作用，团簇数密度随时间呈指数形式衰减，衰减时间常数为Oa_a；两团簇相互离散的相对平均速率V与它们之间的相对距离L在 统计意义上成正比，即V=HL.停止沉积后初期,H≈Oa_a，然后随着扩散时间的增 加，H逐渐趋于零；随着液体基底黏滞系数增加，摩擦力增大，H逐渐减小，摩 关键词： 排斥相互作用 团簇 扩散     

Sign and magnitude of the nucleon-nucleon parity-violating π-exchange potential in the Weinberg-Salam model of weak interactions

We show that, inside a quark model of baryons, the sign of the nucleon-nucleon parity-violating π-exchange potential can be determined.     

Possible new coherence effects in condensed systems with repulsive interactions

A possible new mechanism for high temperature superconductivity is proposed. A system of electrons and nuclei is shown to rearrange into two or more clusters, leading to a conformational stabilization with strong repulsive interactions and very sensitive dependence on the exchange energy. The basic group of electrons are quads. Some remarkable electromagnetic properties of certain AlCAl junctions and anomalous diamagnetic properties of CuCl are suggested to be realizations of our model.