Relationship of field-theory based single boson exchange potentials to current ones

It is shown that field-theory based single boson exchange potentials cannot be identified to those of the Yukawa or Coulomb type that are currently inserted in the Schr\"odinger equation. The potential which is obtained rather corresponds to this current single boson exchange potential corrected for the probability that the system under consideration is in a two-body component, therefore missing contributions due to the interaction of these two bodies while bosons are exchanged. The role of these contributions, which involve at least two boson exchanges, is examined. The conditions that allow one to recover the usual single boson exchange potential are given. It is shown that the present results have some relation: i) to the failure of the Bethe-Salpeter equation in reproducing the Dirac or Klein-Gordon equations in the limit where one of the constituent has a large mass, ii) to the absence of corrections of relative order alpha log(1/alpha) to a full calculation of the binding energy in the case of neutral massless bosons or iii) to large corrections of wave-functions calculated perturbatively in some light-front approaches.Comment: LaTeX, 37 pages, 14 figures, submitted for publicatio

Nucleon-nucleon interaction models and non-locality

The effect of non-locality in the NN interaction models is examined. It is shown that this feature can explain differences in predictions made from models evidencing a difference with this respect. This is done for both static and dynamical observables, taking into account that a non-local term can be transformed away by performing a unitary transformation. Some results for the deuteron form factors, the A(Q^2) structure function and the T_{20}(Q^2) tensor polarization are given as an example. A few cases where discrepancies cannot be explained are also considered. They point to differences in the models as for the deuteron asymptotic normalizations, A_S and A_D, which are not affected by the present analysis.Comment: 6 pages, 6 figures, file.tar, Invited talk (XVIIIth European Conference on Few-Body Problems in Physics), to appear in Few-Body Systems Supplemen

"Point-form" estimate of the pion form factor revisited

The pion form factor calculation in the ``point-form'' of relativistic quantum mechanics is re-considered. Particular attention is given to the relation between the momentum of the system and the momentum transfer as well as to the quark current.Comment: 3 pages, 2 figures, contribution to the 17th International IUAP Conference on Few-Body Problems in Physics, 5-10 June 2003, Durham (USA

Comparison of Form Factors Calculated with Different Expressions for the Boost Transformation

The effect of different boost expressions is considered for the calculation of the ground-state form factor of a two-body system made of scalar particles interacting via the exchange of a scalar boson. The aim is to provide an uncertainty range on methods employed in implementing these effects as well as an insight on their relevance when an ``exact'' calculation is possible. Using a wave function corresponding to a mass operator that has the appropriate properties to construct the generators of the Poincar\'{e} algebra in the framework of relativistic quantum mechanics, form factors are calculated using the boost transformations pertinent to the instant, front and point forms of this approach. Moderately and strongly bound systems are considered with masses of the exchanged boson taken as zero, 0.15 times the constituent mass $m$, and infinity. In the first and last cases, a comparison with ``exact'' calculations is made (Wick-Cutkosky model and Feynman triangle diagram). Results with a Galilean boost are also given. Momentum transfers up to $Q^2=100 m^2$ are considered. Emphasis is put on the contribution of the single-particle current, as usually done. It is found that the present point-form calculations of form factors strongly deviate from all the other ones, requiring large contributions from two-body currents. Different implementations of the point-form approach, where the role of these two-body currents would be less important, are sketched.Comment: Version as accepted for publication, added 6 pages of explanatorial materia

The form factor of the pion in "point-form" of relativistic dynamics revisited

The electromagnetic form factor of the pion is calculated in the "point-form" of relativistic quantum mechanics using simple, phenomenological wave functions. It is found that the squared charge radius of the pion is predicted one order of magnitude larger than the experimental value and the asymptotic behavior expected from QCD cannot be reproduced. The origin of these discrepancies is analyzed. The present results confirm previous ones obtained from a theoretical model and call for major improvements in the implementation of the "point-form" approach.Comment: 8 pages, 3 eps figure

More about the comparison of local and non-local NN interaction models

The effect of non-locality in the NN interaction with an off-energy shell character has been studied in the past in relation with the possibility that some models could be approximately phase-shifts equivalent. This work is extended to a non-locality implying terms that involve an anticommutator with the operator p^2. It includes both scalar and tensor components. The most recent ``high accuracy'' models are considered in the analysis. After studying the deuteron wave functions, electromagnetic properties of various models are compared with the idea that these ones differ by their non-locality but are equivalent up to a unitary transformation. It is found that the extra non-local tensor interaction considered in this work tends to re-enforce the role of the term considered in previous works, allowing one to explain almost completely the difference in the deuteron D-state probabilities evidenced by the comparison of the Bonn-QB and Paris models for instance. Conclusions for the effect of the non-local scalar interaction are not so clear. In many cases, it was found that these terms could explain part of the differences that the comparison of predictions for various models evidences but cases where they could not were also found. Some of these last ones have been analyzed in order to pointing out the origin of the failure.Comment: 32 pages, 24 figure

Parity-Violating Interaction Effects in the np System

We investigate parity-violating observables in the np system, including the longitudinal asymmetry and neutron-spin rotation in np elastic scattering, the photon asymmetry in np radiative capture, and the asymmetries in deuteron photo-disintegration d(gamma,n)p in the threshold region and electro-disintegration d(e,e`)np in quasi-elastic kinematics. To have an estimate of the model dependence for the various predictions, a number of different, latest-generation strong-interaction potentials--Argonne v18, Bonn 2000, and Nijmegen I--are used in combination with a weak-interaction potential consisting of pi-, rho-, and omega-meson exchanges--the model known as DDH. The complete bound and scattering problems in the presence of parity-conserving, including electromagnetic, and parity-violating potentials is solved in both configuration and momentum space. The issue of electromagnetic current conservation is examined carefully. We find large cancellations between the asymmetries induced by the parity-violating interactions and those arising from the associated pion-exchange currents. In the np capture, the model dependence is nevertheless quite small, because of constraints arising through the Siegert evaluation of the relevant E1 matrix elements. In quasi-elastic electron scattering these processes are found to be insignificant compared to the asymmetry produced by gamma-Z interference on individual nucleons.Comment: 65 pages, 26 figures, submitted to PR

Dynamic Response of Two-Electrode Distributed Feedback Laser for Stable Signal Mode Operation

The longitudinal spatial hole burning (LSHB) effect has been known to limit the performance of distributed feedback (DFB) semiconductor lasers to achieve a better dynamic signal mode operation (DSMO). So, in order to ensure a stable (DSMO), we propose a novel device design of two electrode DFB lasers with longitudinal variation in the coupling coefficient (distributed coupling coefficient (DCC)), the structure also contains a phase shifted in middle of the cavity. By means of the finite difference time domain (FDTD) numerical method, we analyze dynamic response of our structure and we also compare the results with the conventional two electrode DFB laser (TE-DFB). The numerical simulation shows that, a better dynamic signal mode has been achieved by TE-DCC-DFB lasers in comparison with TE-DFB laser due to its better and high side mode suppression ratio (SMSR). Therefore, the TE-DCC-DFB lasers will be useful to extend the transmission distance in optical fiber communication systems

An Efficient Face Recognition Using SIFT Descriptor in RGB-D Images

Automatic face recognition has known a very important evolution in the last decade, due to its huge usage in the security systems. The most of facial recognition approaches use 2D image, but the problem is that this type of image is very sensible to the illumination and lighting changes. Another approach uses the 3D camera and stereo cameras as well, but it’s rarely used because it requires a relatively long processing duration. A new approach rise in this field, which is based on RGB-D images produced by Kinect, this type of cameras cost less and it can be used in any environment and under any circumstances. In this work we propose a new algorithm that combines the RGB image with Depth map which is less sensible to illumination changes. We got a recognition rate of 96, 63% in rank 2

Cross-ladder effects in Bethe-Salpeter and Light-Front equations

Bethe-Salpeter (BS) equation in Minkowski space for scalar particles is solved for a kernel given by a sum of ladder and cross-ladder exchanges. The solution of corresponding Light-Front (LF) equation, where we add the time-ordered stretched boxes, is also obtained. Cross-ladder contributions are found to be very large and attractive, whereas the influence of stretched boxes is negligible. Both approaches -- BS and LF -- give very close results.Comment: 11 pages, 7 figure