6742150
Gauge invariance and Compton scattering from relativistic composite systems.
Using the Ward-Takahashi (WT) identity and the Bethe-Salpeter wave equation, we investigate the dynamical requirements imposed by electromagnetic gauge invariance on Compton scattering from relativistic composite systems. The importance of off-shell rescattering in intermediate states, which is equivalent to final state interactions in inclusive processes, is clarified in the context of current conservation. It is shown that, if the nuclear force is nonlocal, there will be both two-photon interaction currents and rescattering contributions to terms involving one-photon interaction currents. We derive the two-body WT identity for the two-photon interaction currents, and obtain explicit forms for the interaction current operators for three illustrative models of nuclear forces: (a) two-pion exchange forces with baryon resonances, (b) covariant separable forces, and (c) charged one-pion exchange.
118704383
Nucleon and N‐Delta Electromagnetic Transition Form Factors
We consider the baryons as three constituent valence quark systems. Their dynamics is described by the covariant Spectator formalism [1,2] for a quark-diquark system, where the diquark is always on its mass-shell. The electromagnetic interaction is considered in the relativistic impulse interaction (RIA) where the photon couples with the quark through the current j M = j\y^ + 72 l°2mV (m *s ^ e n u c l e o n mass). The two form factors j'l and 72 account for all QCD mechanisms (qq pairs, pion cloud and gluon sea effects). Only the 71 form factor includes pion cloud effects in its isovector part. The nucleon wave function consists of spin-0 (isospin-0) and spin-1 (isospin-l) components written in terms of the diquark polarization vectors and the nucleon Dirac spinor [1]. Furthermore, it verifies the Dirac equation and generates the correct structure for its non-relativistic limit. Current conservation is also satisfied. The Jlab polarization data of the electromagnetic nucleon elastic form factors are described [3,4] when one assumes an S-state for the quark-diquark system [1], which means that the data does not signal any angular dependence in the wave function. The results show that spherical charge and matter distributions aremore » compatible with the data, even when we consider Spin Direction Dependent density definitions [5]. The explicit consideration of the pion cloud effects definitively improves the description of the nucleon form factors [1]. We also calculated the N-Delta transition form factors. Preliminary results considering the Delta wave function as a mixture of a S and a D state explain the magnetic dipole G*M and the electric quadrupole G*E data [6]. Improvements are underway in order to describe also the Coulomb quadrupole form factor G£« less
119626591
Relativistic effects in few nucleon systems
Abstract The discussion session on relativistic effects was moderated by Professor Walter Glockle, of the Universitat Bochum. This report is divided into two main sections on (1) relativistic few body equations and (2) relativistic calculations of matrix elements. In some places the discussion is incorporated into the text, but a number of issues pertaining to the first topic are summarized separately in part 1.3.
125805875
HADRONIC DECAYS OF LOW LYING GLUEBALLS
118254960
Relativistic theory of few body systems and their electromagnetic interactions
Recent results obtained from the manifestly covariant spectator theory are summarized. A recent unpublished best fit to NN scattering using 13 OBE parameters gives x{sup 2}=2.25 and a triton binding energy of {minus}8.491 MeV. This agreement is possible because of the existence of off-shell coupling of the phenomenological, intermediate range effective scalar exchanges (both isoscalar and isovector). The previously published results for the deuteron form factors are reviewed, and new, preliminary results for electrodisintegration of the deuteron are presented.
125810230
Complete measurements of scalar and pseudoscalar electroproduction
44953286
String perturbation theory diverges.
We prove that perturbation theory for the bosonic string diverges for arbitrary values of the coupling constant and is not Borel summable. This divergence is independent of the existence of the infinities that occur in the theory due to the presence of tachyons and dilaton tadpoles. We discuss the physical implications of such a divergence.
35211494
Nonperturbative solution of the Ising model on a random surface.
The two-matrix-model representation of the Ising model on a random surface is solved exactly to all orders in the genus expansion. The partition function obeys a fourth-order nonlinear differential equation as a function of the string coupling constant. This equation differs from that derived for the k=3 multicritical one-matrix model, thus disproving that this model describes the Ising model. A similar equation is derived for the Yang-Lee edge singularity on a random surface, and is shown to agree with the k=3 multicritical one-matrix model.
26869196
Mean-field theory of the Potts glass.
Etude du gel de spins de Potts, a l'etat p et avec interaction aleatoire, en une phase verre de Potts, ou la symetrie de Potts n'est pas brisee en moyenne. Differences avec les verres de spin: les deux phases verre de Potts se distinguent par la nature des correlations entre les divers etats fondamentaux degeneres du systeme