9092550
Scalar and vector interactions of a composite spin-1/2 system.
Scalar and vector interactions, with the scalar interaction coupled to a composite spin-1/2 system so as to cause a shift of its mass, are shown to obey a low-energy theorem which guarantees that the second order interaction is the same as for a point Dirac particle, in which case the second-order interaction comes from z graphs. Off-shell and contact interactions appropriate to the composite system cancel and this is verified in a model of a composite fermion. The low-energy theorem and its generalizations provide a justification for the use of the Dirac equation as it has been used in relativistic nuclear scattering and mean field theories.
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 A recent unpublished best fit to NN scattering using 13 OBE parameters gives x{sup 2}=2.25 and a triton binding energy of {minus}8.491 MeV.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.
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
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.
40501364
Nonperturbative two-dimensional quantum gravity.
We propose a nonperturbative definition of two-dimensional quantum gravity, based on a double-scaling limit of the random-matrix model. We derive an exact differential equation for the partition function of two-dimensional gravity coupled to conformal matter as a function of the string coupling constant that governs the genus expansion of two-dimensional surfaces, and discuss its properties and consequences. We also construct and discuss the correlation functions of an infinite set of local operators for spherical topology.
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.
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.