\bar{p}p low energy parameters from annihilation cross section data

The recent experimental data obtained by the OBELIX group on total $\bar{p}p$ annihilation cross section are analysed; the low energy spin averaged parameters of the $\bar{p}p$ scattering amplitude (the imaginary parts of the S-wave scattering length and P-wave scattering volume) are extracted from the data. Their values are found to be equal to $Im a_{sc} = - 0.69 \pm 0.01 (stat) \pm 0.03 (sys) fm, Im A_{sc} = - 0.76 \pm 0.05 (stat) \pm 0.04 (sys) fm^3$. The results are in very good agreement with existing atomic data.Comment: latex.tar.gz file, 8 pages, 1 figur

The Continuum Spectrum of the 4N System. Results and Challenges

The recent calculation of the four nucleon continuum spectrum are reviewed. Faddeev-Yakubovsky equations in configuration space have been solved for the four nucleon system with special interest in their scattering states. We present results concerning the structure of the first $^4$He, scattering states in different (T,S) channels including the first inelatic threshold N+3N$\to$NN+NN and the n-t cross section using realistic potentials.Comment: 9 pages, 8 Figures Contribution to the 16th International IUPAP conference on Few-Body Problems in Physics, Taipei 6-10 march 2000. to be published in Nucl. Phy

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

Solutions of the Wick-Cutkosky model in the Light-Front Dynamics

We study relativistic effects in a system of two scalar particles interacting via a scalar exchange in the Light Front Dynamcis framework. The results are compared to those provided by Bethe-Salpeter and non relativistic equations. It is found in particular that for massive exchange, the relativistic description is of crucial importance even in the limit of zero binding energy. PACS: 11.10, 03.70, 03.65P Keywords: Light-Front Dynamics, Relativistic equations, Quantum Field TheoryComment: 12 pages, 11 figures, Latex.tar.gz file Accepted in Phys. Lett.

Application of complex-scaling method for few-body scattering

Formalism based on complex-scaling method is developed for solving the few particle scattering problem by employing only trivial boundary conditions. Several applications are presented proving efficiency of the method in describing elastic and three-body break-up reactions for Hamiltonians which may include both short and long-range interaction

Complex scaling method for three- and four-body scattering above the break-up thresholds

A formalism based on the complex-scaling method is presented to solve the few particle scattering problem in configuration space using bound state techniques with trivial boundary conditions. Several applications to A=3,4 systems are presented to demonstrate the efficiency of the method in computing elastic as well as break-up reactions with Hamiltonians including both short and long-range interaction.Comment: FB20 conference proceeding

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

Self-Paced Multitask Learning with Shared Knowledge

This paper introduces self-paced task selection to multitask learning, where instances from more closely related tasks are selected in a progression of easier-to-harder tasks, to emulate an effective human education strategy, but applied to multitask machine learning. We develop the mathematical foundation for the approach based on iterative selection of the most appropriate task, learning the task parameters, and updating the shared knowledge, optimizing a new bi-convex loss function. This proposed method applies quite generally, including to multitask feature learning, multitask learning with alternating structure optimization, etc. Results show that in each of the above formulations self-paced (easier-to-harder) task selection outperforms the baseline version of these methods in all the experiments