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S. A. Sofianos

Publications and source records attributed to S. A. Sofianos.

52 records · Page 3Linked to original sources
arXiv1997

Existence and transitions properties of three-deuteron muonic molecule (3d 2e^- μ^-)

We calculated the energy and the size of the three-deuteron muonic molecule (3d 2e^- μ^-) = D_3 μ. It turns out that this system possesses two equilibrium positions, one at distances typical for muonic molecules and a second one at the usual molecular size. We show, moreover, that the fusion probability of the three deuterons is considerably enhanced due to the existence of a ^6Li^* threshold resonance. Our estimates indicate that this probability is considerably higher than the decay rate of the competing Auger transition.

nucl-th↗
arXiv1997

Jost Function for Coupled Partial Waves

An exact method for direct calculation of the Jost functions and Jost solutions for non-central potentials which couple partial waves of different angular momenta is presented. A combination of the variable-constant method with the complex coordinate rotation is used to replace the matrix Schrödinger equation by an equivalent system of linear first--order differential equations. Solving these equations numerically, the Jost functions can be obtained to any desired accuracy for all complex momenta of physical interest, including the spectral points corresponding to bound and resonant states. The effectiveness of the method is demonstrated using the Reid soft-core and Moscow nucleon-nucleon potentials which involve tensor forces.

nucl-th↗
arXiv1997

Bound States and Scattering Processes in the ^4He_3 Atomic System

We present a mathematically rigorous method for solving three-atomic bound state and scattering problems. The method is well suited for applications in systems where the inter-atomic interaction is of a hard-core nature. It has been employed to obtain the ground- and excited-state energies for the Helium trimer and to calculate, for the first time, the scattering phase shifts and wave-functions for the He atom-He dimer at ultra-low energies.

physics.chem-ph↗
arXiv1997

Nuclear Fusion via Triple Collisions in Solar Plasma

We consider several nuclear fusion reactions that take place at the center of the sun, which are omitted in the standard pp-chain model. More specifically the reaction rates of the nonradiative production of ^3He, ^7Be, and ^8B nuclei in triple collisions involving electrons are estimated within the framework of the adiabatic approximation. These rates are compared with those of the corresponding binary fusion reactions.

nucl-th↗
arXiv1997

On the possibility of eta-mesic nucleus formation

A microscopic treatment of eta-nucleus system is presented. Using this, the poles of the amplitude describing elastic scattering of eta-meson off the light nuclei ^2H, ^3H, ^3He, and ^4He have been located in the second quadrant of the complex plane of the eta-nucleus relative momentum. The results obtained indicate that, within the existing uncertainties in the eta-Nucleon input data, a bound state could exist. By a qualitative consideration it is shown that such bound-states, cannot be narrow. It is further shown that scattering length calculations cannot provide a definite answer on the question concerning the existence of eta-nucleus bound states.

nucl-th↗
arXiv1997

Sub-threshold resonances in few-neutron systems

Three- and four-neutron systems are studied within the framework of the hyperspherical approach with a local S-wave nn-potential. Possible bound and resonant states of these systems are sought as zeros of three- and four-body Jost functions in the complex momentum plane. It is found that zeros closest to the origin correspond to sub-threshold (nnn) (1/2-) and (nnnn) (0+) resonant states. The positions of these zeros turned out to be sensitive to the choice of the $nn$--potential. For the Malfliet- Tjon potential they are E(nnn)=-4.9-i6.9 (MeV) and E(nnnn)=-2.6-i9.0 (MeV). Movement of the zeros with an artificial increase of the potential strength also shows an extreme sensitivity to the choice of potential. Thus, to generate ^3n and ^4n bound states, the Yukawa potential needs to be multiplied by 2.67 and 2.32 respectively, while for the Malfliet-Tjon potential the required multiplicative factors are 4.04 and 3.59.

nucl-th↗
arXiv1997

Eta-meson light nucleus scattering and Charge Symmetry Breaking

The η-meson collision with light nuclei, ^2H, ^3H, ^3He, and ^4He, is considered on the basis of a microscopic approach which utilises Faddeev type and Lippmann-Schwinger equations. The nuclear hamiltonian is approximated by the finite rank approximation which amounts to the coherent approximation. The η-nucleus scattering length and the resonance and bound--state poles of the amplitude describing elastic scattering of η-meson by these nuclei are obtained. For each of the nuclei considered, the minimal factor enhancing the ηN--attraction that moves the poles to the quasi--bound state area of the complex k--plane, is determined. It is shown that within the existing uncertainties in the elementary ηN iteraction all these nuclei can support a quasi--bound state which can result in a formation of an eta-mesic nucleus. Various aspects of the eta-nucleus physics are discussed with specific emphasis given to the η--nucleus effective interaction in configuration space (constructed via the Marchenko inverse scattering method), to the Okubo--Zweig--Iizuka (OZI) rule, and to the charge symmetry breaking problem.

nucl-th↗
arXiv1996

Nonradiative proton--deuteron fusion in stellar plasma

The nuclear reaction e+p+d -----> He3 + e is considered at thermonuclear energies. The motion of the electron is treated within the adiabatic approximation and the pd scattering state is constructed in the form of an antisymmetrized product of the bound state wave function of the deuteron and of the wave function of the pd relative motion. The latter is calculated using an effective pd potential constructed via the Marchenko inverse scattering method. The bound state wave function of He3 is obtained using Faddeev--type integrodifferential equations. The reaction rate thus obtained for the solar interior conditions is approximately 10^{-4} of the corresponding rate for the radiative capture pd ----> He3 + gamma .

nucl-th↗
arXiv1996

Exact method for locating potential resonances and Regge trajectories

We propose an exact method for locating the zeros of the Jost function for analytic potentials in the complex momentum--plane. We further extend the method to the complex angular--momentum plane to provide the Regge trajectories. It is shown, by using several examples, that highly accurate results for extremely wide as well as for extremely narrow resonances with or without the presence of the Coulomb interaction can be obtained.

nucl-th↗
arXiv1996

The eta-meson light nucleus resonances and quasi-bound states

The position and movement of poles of the amplitude for elastic eta-meson scattering off the light nuclei d, t, ^3He, and ^4He are studied. It is found that, within the existing uncertainties for the elementary eta-N interaction, all these nuclei can support a quasi-bound state. The values of the eta-nucleus scattering lengths corresponding to the critical eta-N interaction which produces a quasi--bound state are given.

nucl-th↗
arXiv1995

On the possibility of an eta-meson light nucleus bound state formation

The resonance and bound--state poles of the amplitude describing elastic scattering of $η$-meson off the light nuclei $^2H$,\,$^3H$,\, $^3He$, and $^4He$ are calculated in the framework of a microscopic approach based on few--body equations. For each of the nuclei, the two--body parameters that enhance the $ηN$--attraction which generate quasi--bound states, are also determined.

nucl-th↗
arXiv1995

Interaction of eta-meson with light nuclei

A microscopic treatment of $η$--nucleus scattering is presented. When applying the underlying exact integral equations, the excitation of the target are neglected, and an input $ηN$ amplitude is chosen which reproduces the $S_{11}(1535)$ resonance. It is shown that the $η$--nucleus scattering lengths are quite sensitive to the $ηN$ parameters and the nuclear wave functions. For a special choice of the parameters an $η{^4\!H}e$ quasi--bound state occurs.

nucl-th↗
arXiv1995

Resonant nuclear transition in the d-mu-Li6 muonic molecule

The reaction rate of the nuclear fusion d+Li6 ----> Be8*(2+,0) is estimated in the case where the nuclei are confined to each other by a muon. For the description of nuclear transitions, a method which is analogous to the Linear Combination of Atomic Orbitals has been used. Using the complex coordinate rotation method, we found that a molecular d-mu-Li6 state exists with energy (-20.3084-i0.0066) eV and |Ψ_{m}(0)|=0.44x10^{-7} fm^-3/2. The nuclear wave functions needed, were constructed in the form of antisymmetrized products of harmonic-oscillator functions for the three-cluster approximation, (ddα), to the five-body (NNNNα) problem. It was found that the reaction rate λis strongly dependent on the energy gap between the d-Li6 threshold and the energy of the final Be8^* resonant state. The value of λobtained by averaging over the width of this resonance, is 0.183x10^10 sec^{-1}.

nucl-th↗
arXiv1995

A METHOD OF CALCULATING THE JOST FUNCTION FOR ANALYTIC POTENTIALS

A combination of the variable-constant and complex coordinate rotation methods is used to solve the two-body Schrödinger equation. The latter is replaced by a system of linear first-order differential equations, which enables one to perform direct calculation of the Jost function for all complex momenta of physical interest, including the spectral points corresponding to bound and resonance states. Explicit forms of the equations, appropriate for central, noncentral, and Coulomb-tailed potentials are given. Within the proposed method, the scattering, bound, virtual, and resonance state problems can be treated in a unified way. The effectiveness of the method is demonstrated by a numerical example.

nucl-th↗
arXiv1995

Threshold scattering of the eta-meson off light nuclei

The scattering lengths of eta-meson collisions with light nuclei d,t,3He, and 4He are calculated on the basis of few-body equations in coherent approximation. It is found that the eta-nucleus scattering length depends strongly on the number of nucleons and the potential-range parameter. By taking into account the off-shell behavior of the eta-N amplitude, the eta-4He scattering length increases considerably.

nucl-th↗