10889898
Unitary, gauge invariant, relativistic resonance model for pion photoproduction.
Pion photoproduction up to 770 MeV photon laboratory energy is described by a manifestly covariant wave equation, which includes a treatment of the final state {pi}N interactions consistent with the covariant, unitary, resonance model of pi-N scattering previously developed. The kernel of the equation includes nucleon (N), Roper (N*), Delta, and D{sub 13} poles and their crossed poles, as well as {pi}, {mu}, and w exchange terms. The Kroll-Ruderman term and other interaction currents insure that the model is exactly gauge invariant to all orders in the strong coupling, g{sub {pi}NN}, and that the low energy theorem is satisfied. Unitarity is maintained up to first order in the charge e (Watson theorem). The complete development of this model, which gives a good fit to all the data up to 770 MeV, is presented.
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
125810230
Complete measurements of scalar and pseudoscalar electroproduction
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.
125805875
HADRONIC DECAYS OF LOW LYING GLUEBALLS
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.
32193057
High-energy symmetries of string theory.
By means of a recent analysis of the high-energy limit of string scattering, linear relations between string scattering amplitudes are derived. These are shown to hold order by order in perturbation theory. If one assumes that they hold for the full theory, they suggest the existence of an enormous string-broken symmetry which is restored at high energies. Some speculations as to the nature of this symmetry are presented.
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
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.