Small clusters of fermions

By comparing respectively the interaction between 3He atoms and the neutron-neutron one, we examine the possibility for both fermionic systems to form small clusters.Comment: Contributed talk to 17th International IUPAP Conference on Few-Body Problems in Physics, Durham, North Carolina, 5-10 June 2003. Published in the proceedings (Elsevier, 2004) pp. S106-S10

Ab-initio calculations of four-nucleon elastic scattering

We present microscopic calculations of low energy scattering observables in all possible four nucleon systems : n-3H, p-3He and p-3H. Results were obtained by solving Faddeev-Yakubovski equations in configuration space, appropriately modified to include Coulomb and three-nucleon forces

Four nucleon systems : a zoom to the open problems in nuclear interaction

Faddeev-Yakubovski equations in configuration space are used to solve four nucleon problem for bound and scattering states. Different realistic interaction models are tested, elucidating open problems in nuclear interaction description. On one hand, by example of nonlocal Doleschall potential, we reveal possibility of reducing three-nucleon force. On the other hand we disclose discrepancies in describing n+$^3$H resonance, which seems to be hardly related with off-shell structure of nucleon-nucleon interaction.Comment: 8 pages ; 3 fig

Scattering of heavy charged particles on hydrogen atoms

The low energy scattering of heavy positively charged particles on hydrogen atoms (H) are investigated by solving the Faddeev equations in configuration space. A resonant value of the pH scattering length, $a=750\pm 5$ a.u., in the pp antisymmetric state was found. This large value indicates the existence of a first excited state with a binding energy B=1.14$\times10^{-9}$ a.u. below the H ground state. Several resonances for non zero angular momenta states are predicted.Comment: 8 pages, 9 figures, contribution to International Workshop "Dynamics and structure of critically stable quantum few-body systems" held at Les Houches, France, October 8-13, 2001. To appear in Few-Body Physic

Coulomb effects in four nucleon continuum states

The Faddeev-Yakubovski equations are solved in configuration space for low energy four-nucleon continuum states. Coulomb interaction was included into the formalism permitting an exact description of the scattering states in p+$^{3}$He and p+$^{3}$H systems

On the possibility of generating a 4-neutron resonance with a {\boldmath T=3/2T=3/2} isospin 3-neutron force

We consider the theoretical possibility to generate a narrow resonance in the four neutron system as suggested by a recent experimental result. To that end, a phenomenological $T=3/2$ three neutron force is introduced, in addition to a realistic $NN$ interaction. We inquire what should be the strength of the $3n$ force in order to generate such a resonance. The reliability of the three-neutron force in the $T=3/2$ channel is exmined, by analyzing its consistency with the low-lying $T=1$ states of $^4$H, $^4$He and $^4$Li and the $^3{\rm H} + n$ scattering. The {\it ab initio} solution of the $4n$ Schr\"{o}dinger equation is obtained using the complex scaling method with boundary conditions appropiate to the four-body resonances. We find that in order to generate narrow $4n$ resonant states a remarkably attractive $3N$ force in the $T=3/2$ channel is required.Comment: 11 pages, 11 figures, minor change, published version, to be published in Physical Review

Bound state techniques to solve the multiparticle scattering problem

Solution of the scattering problem turns to be very difficult task both from the formal as well as from the computational point of view. If the last two decades have witnessed decisive progress in ab initio bound state calculations, rigorous solution of the scattering problem remains limited to A$\leq$4 case. Therefore there is a rising interest to apply bound-state-like methods to handle non-relativistic scattering problems. In this article the latest theoretical developments in this field are reviewed. Five fully rigorous methods will be discussed, which address the problem of nuclear collisions in full extent (including the break-up problem) at the same time avoiding treatment of the complicate boundary conditions or integral kernel singularities. These new developments allows to use modern bound-state techniques to advance significantly rigorous solution of the scattering problem.Comment: To appear in Progress in Particle and Nuclear Physic

The spatial damping of magnetohydrodynamic waves in a flowing partially ionised prominence plasma

Solar prominences are partially ionised plasmas displaying flows and oscillations. These oscillations show time and spatial damping and, commonly, have been explained in terms of magnetohydrodynamic (MHD) waves. We study the spatial damping of linear non-adiabatic MHD waves in a flowing partially ionised plasma, having prominence-like physical properties. We consider single fluid equations for a partially ionised hydrogen plasma including in the energy equation optically thin radiation, thermal conduction by electrons and neutrals, and heating. Keeping the frequency real and fixed, we have solved the obtained dispersion relations for the complex wavenumber, k, and have analysed the behaviour of the damping length, wavelength and the ratio of the damping length to the wavelength, versus period, for Alfven, fast, slow and thermal waves.Comment: 28 pages, 9 figure

The statistical significance of the N-S asymmetry of solar activity revisited

The main aim of this study is to point out the difficulties found when trying to assess the statistical significance of the North-South asymmetry (hereafter SSNSA) of the most usually considered time series of solar activity. First of all, we distinguish between solar activity time series composed by integer or non-integer and dimensionless data, or composed by non-integer and dimensional data. For each of these cases, we discuss the most suitable statistical tests which can be applied and highlight the difficulties to obtain valid information about the statistical significance of solar activity time series. Our results suggest that, apart from the need to apply the suitable statistical tests, other effects such as the data binning, the considered units and the need, in some tests, to consider groups of data, affect substantially the determination of the statistical significance of the asymmetry. Our main conclusion is that the assessment of the statistical significance of the N-S asymmetry of solar activity is a difficult matter and that an absolute answer cannot be given, since many different effects influence the results given by the statistical tests. In summary, the quantitative results about the statistical significance of the N-S asymmetry of solar activity provided by different authors, as well as the studies about its behaviour, must be considered with care because they depend from the chosen values of different parameters or from the considered units.Comment: Astronomy and Astrophysics Latex, 9 pages, 4 figure