Construction of Consistent Meson Exchange Currents by Laplace Transform

We propose a new method for the construction of a consistent meson exchange current in $r$-space for the spin-isospin dependent central and tensor part of phenomenological nucleon-nucleon potentials by using a Laplace transformation, which allows the representation by a finite number of Yukawa functions. This method is applied to the Paris and the recent Argonne $V_{18}$ potentials. Results are presented for electrodisintegration of the deuteron near threshold.Comment: 13 pages Revtex including 9 figures, final version accepted for publication in EPJA (one figure and discussion added

The two-nucleon system in the Δ\Delta region including full meson retardation

A model is developed for the hadronic and electromagnetic interaction in the two-nucleon system above pion threshold in the framework of meson, nucleon and $\Delta$ degrees of freedom. It is based on time-ordered perturbation theory and includes full meson retardation in potentials and exchange currents as well as loop contributions to the nucleonic one-body current. Results for $NN$ scattering and deuteron photodisintegration are presented.Comment: 4 pages Revtex including 2 figures, contribution to "Mesons and Light Nuclei 2001", Prague, July 2-6, 200

New inversion methods for the Lorentz Integral Transform

The Lorentz Integral Transform approach allows microscopic calculations of electromagnetic reaction cross sections without explicit knowledge of final state wave functions. The necessary inversion of the transform has to be treated with great care, since it constitutes a so-called ill-posed problem. In this work new inversion techniques for the Lorentz Integral Transform are introduced. It is shown that they all contain a regularization scheme, which is necessary to overcome the ill-posed problem. In addition it is illustrated that the new techniques have a much broader range of application than the present standard inversion method of the Lorentz Integral Transform.Comment: 12 pages. 12 figures, revtex4. submitted to Eur.Phys.J.

The Luminosity Function of the Hot and Cold Kuiper belt Populations

Abridged. We have performed an ecliptic survey of the Kuiper belt, with an areal coverage of 8.9 square degrees to a 50% limiting magnitude of r'=24.7, and have detected 88 Kuiper belt objects, roughly half of which received follow-up one to two months after detection. Using this survey data alone, we have measured the luminosity function of the Kuiper belt, thus avoiding any biases that might come from the inclusion of other observations. We have found that the Cold population defined as having inclinations less than 5 degrees has a luminosity function slope alpha=0.82+-0.23, and is different from the Hot population, which has inclinations greater than 5 degrees and a luminosity function slope alpha=0.35+-0.21. As well, we have found that those objects closer than 38 AU have virtually the same luminosity function slope as the Hot population. This result, along with similar findings of past surveys demonstrates that the dynamically cold Kuiper belt objects likely have a steep size distribution, and are unique from all of the excited populations which have much shallower distributions. This suggests that the dynamically excited population underwent a different accretion history and achieved a more evolved state of accretion than the cold population. As well, we discuss the similarities of the Cold and Hot populations with the size distributions of other planetesimal populations. We find that while the Jupiter family comets and the scattered disk exhibit similar size distributions, a power-law extrapolation to small sizes for the scattered disk cannot account for the observed influx of comets. As well, we have found that the Jupiter Trojan and Hot populations cannot have originated from the same parent popuation, a result that is difficult to reconcile with scattering models similar to the NICE model.Comment: Accepted for publication in Icarus. 27 pages, 10 figures, 4 table

Spin Asymmetry and Gerasimov-Drell-Hearn Sum Rule for the Deuteron

An explicit evaluation of the spin asymmetry of the deuteron and the associated GDH sum rule is presented which includes photodisintegration, single and double pion and eta production as well. Photodisintegration is treated with a realistic retarded potential and a corresponding meson exchange current. For single pion and eta production the elementary operator from MAID is employed whereas for double pion production an effective Lagrangean approach is used. A large cancellation between the disintegration and the meson production channels yields for the explicit GDH integral a value of 27.31 $\mu$b to be compared to the sum rule value 0.65 $\mu$b.Comment: 4 pages, 5 figures, revtex

Offshell effects in electromagnetic reactions on the deuteron

Offshell contributions to the electromagnetic nuclear current are evaluated within a nonrelativistic approach by incorporation one-pion loop contributions in time-ordered perturbation theory. By construction, the correct experimental onshell properties of the nucleon current are ensured so that only the genuine offshell effects appear as model dependent. For a qualitative assessment of such offshell effects, this model is applied to photodisintegration of the deuteron for photon energies up to 500 MeV. While at low energies offshell contributions are small, above 300 MeV they lead to sizeable effects in observables up to about 30 percent pointing to the necessity of incorporating such effects if one aims at theoretical predictions of high precision.Comment: 22 pages revtex including 17 figure

The Role of Meson Retardation in the NN Interaction above Pion Threshold

A model is developed for the hadronic interaction in the two-nucleon system above pion threshold which is based on meson, nucleon and $\Delta$ degrees of freedom and which includes full meson retardation in the exchange operators. For technical reasons, the model allows maximal one meson to be present explicitly. Thus the Hilbert space contains besides $NN$ and $N\Delta$ also configurations consisting of two nucleons and one meson. For this reason, only two- and three-body unitarity is obeyed, and the model is suited for reactions in the two nucleon sector only, where one pion is produced or absorbed. Starting from a realistic pure nucleonic retarded potential, which had to be renormalized because of the additional $\pi$ and $\Delta$ degrees of freedom, a reasonable fit to experimental $NN$-scattering data could be achieved.Comment: 30 pages revtex including 17 figures, outline of model and discussion shortened, typos correcte

The Small Numbers of Large Kuiper Belt Objects

We explore the brightness distribution of the largest and brightest (m(R) 5°) from the very brightest to m(R) = 23. We find for m(R) ≾ 23, a single slope appears to describe the luminosity function. We estimate that ~12 KBOs brighter than m(R) ~ 19.5 are present in the Kuiper Belt today. With nine bodies already discovered this suggests that the inventory of bright KBOs is nearly complete

NN korelacije i međudjelovanja u konačnom stanju u (e,e′NN) reakcijama

After a brief overview of relevant studies on one-nucleon knockout, showing the importance of quantitatively understanding the origin of the quenched spectroscopic factors extracted from data, attention is focussed on two-nucleon emission as a suitable tool to investigate nucleon-nucleon correlations inside complex nuclei. In particular, direct (e,e′pp) and (e,e′pn) reactions are discussed, and the role of final-state interactions is studied. The influence of the mutual interaction between the two outgoing nucleons is shown to depend on the kinematics and on the type of the considered reaction.Nakon kratkog pregleda istraživanja izbacivanja jednog nukleona, koji ukazuje na važnost kvantitativnog razumijevanja uzroka malih spektroskopskih faktora dobivenih iz mjernih podataka, pažnja se usmjerava na dvonukleonsku emisiju koja je pogodan proces za istraživanje korelacija nukleon-nukleon u kompleksnim jezgrama. Posebno se raspravljaju izravne (e,e′pp) i (e,e′pn) reakcije i proučava uloga međudjelovanja u konačnom stanju. Pokazuje se da uzajamno djelovanje među izlaznim nukleonima ovisi o kinematici i vrsti ispitivane reakcije