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.
121273546
A Mechanism for Quark Confinement
I shall describe in this lecture a new approach to the dynamics of quarks. It is widely believed that the strong interactions are described by QCD, a nonabelian (SU(3)) gauge theory of colored quarks and gluons, permanently confined in color singlet hadronic bound states. Our knowledge of the nature of the constituents of hadrons derives from their observed symmetries, the success of various phenomenological models such as the quark model and most important from the observed short distance behavior of hadronic currents. It is this free-field theory behavior at large momentum (asymptotic freedom) that singles out nonabelian gauge interactions as the source of the strong interactions, allows us to directly observe the quantum numbers of the quarks and to derive quantative predictions that can test the validity of the theory.
36890636
The Triumph and limitations of quantum field theory
Talk presented at the conference ``Historical and Philosophical Reflections on the Foundations of Quantum Field Theory,'' at Boston University, March 1996. It will be published in the proceedings of this conference.
124543277
Are instantons found
It is argued that the recent prediction of the a dependence of the coupling, g (a), of an effective lattice gauge theory for quarkless qauntum chromodynamics is confirmed by a recent numerical evaluation of g (a) for a latticized SU(2) gauge theory, thus providing strong evidence for the dynamical role of instantons. Additional predictions, testing the validity of the quantum chromodynamics bag model, are presented.
120775506
Density of states in the presence of a strong magnetic field and random impurities
Abstract A supersymmetric formalism is used to rederive a recent beautiful result of Wegner concerning the density of state of an electron gas in the presence of a strong magnetic field and impurities. The derivation is simple and applicable to any (local) distribution of scatterers. Explicit formulae are given in two dimensions. A Poisson distribution of scatterers leads to an interesting condensation phenomenon when the magnetic field is increased.
170218458
The discovery of asymptotic freedom and the emergence of QCD
T he progress of science is much more muddled than is depicted in most history books. This is especially true of theoretical physics, partly because history is written by the victorious. Consequently, historians of science often ignore the many alternate paths that people wandered down, the many false clues they followed, the many misconceptions they had. These alternate points of view are less clearly developed than the final theories, harder to understand and easier to forget, especially as these are viewed years later, when it all really does make sense. Thus, reading history one rarely gets the feeling of the true nature of scientific development, in which the element of farce is as great as the element of triumph.

The emergence of QCD is a wonderful example of the evolution from farce to triumph. During a very short period, a transition occurred from experimental discovery and theoretical confusion to theoretical triumph and experimental confirmation. In this Nobel lecture, I shall describe the turn of events that led to the discovery of asymptotic freedom, which in turn led to the formulation of QCD, the final element of the remarkably comprehensive theory of elementary particle physics—the Standard Model. I shall then briefly describe the experimental tests of the theory and the implications of asymptotic freedom.

The early 1960s, when I started my graduate studies at UC Berkeley, were a period of experimental supremacy and theoretical impotence. The construction and utilization of major accelerators were proceeding at full steam. Experimental discoveries and surprises appeared every few months. There was hardly any theory to speak of. The emphasis was on phenomenology, and there were only small islands of theoretical advances here and there. Field theory was in disgrace; S-Matrix theory was in full bloom. Symmetries were all of the rage. Of the four forces …
9012138
Two-pion-exchange potential and the pi N amplitude.
The authors discuss the two-pion exchange potential which emerges from a box diagram with one nucleon (the spectator) restricted to its mass shell, and the other nucleon line replaced by a subtracted, covariant {pi}N scattering amplitude which includes {Delta}, Roper, and D{sub 13} isobars, as well as contact terms and off-shell (non-pole) dressed nucleon terms. The {pi}N amplitude satisfies chiral symmetry constraints and fits {pi}N data below {approximately} 700 MeV pion energy. They find that this TPE potential can be well approximated by the exchange of an effective sigma and delta meson, with parameters close to the ones used in one-boson-exchange models that fit NN data below the pion production threshold.
12359775
Covariant, chirally symmetric, confining model of mesons.
We introduce a new model of mesons as quark-antiquark bound states. The model is covariant, confining, and chirally symmetric. Our equations give an analytic solution for a zero-mass pseudoscalar bound state in the case of exact chiral symmetry, and also reduce to the familiar, highly successful nonrelativistic linear potential models in the limit of heavy-quark mass and lightly bound systems. In this fashion we are constructing a unified description of all the mesons from the {pi} through the {Upsilon}. Numerical solutions for other cases are also presented.
39922025
Pseudoscalar pi N coupling and relativistic proton-nucleus scattering.
Relativistic p-/sup 40/Ca elastic scattering observables are calculated using relativistic NN amplitudes obtained from the solution of a two-body relativistic equation in which one particle is kept on its mass-shell. Results at 200 MeV are presented for two sets of NN amplitudes, one with pure pseudo-vector coupling for the pion and another with a 25% admixture of pseudo-scalar coupling. Both give a very good fit to the positive energy on-shell NN data. Differences between the predictions of these two models (which are shown to be due only to the differences in their corresponding negative energy amplitudes) provide a measure of the uncertainty in constructing Dirac optical potentials from NN amplitudes. 12 refs., 2 figs.
26437398
Isoscalar meson exchange currents and the deuteron form factors.
The electromagnetic form factors for the RhoPiGamma and wSigmaGamma vertices are calculated from quark loop diagrams which take the qq structure of the Pi, Sigma, Rho, w mesons into account.The resulting form factors decrease with increasing Q 2 (the square of the four-momentum of the off-shell photon) considerably more rapidly than the monopole form factors obtained from vector meson dominance.The implications of this behavior, which has a significant effect on the elastic electromagnetic form factors of deuteron, is discussed.
1424369
Current conservation and interaction currents with relativistic separable interactions.
A method of minimal substitution is used to obtain the electromagnetic two-body interaction current operator associated with a relativistic separable interaction. The result is shown to satisfy a general restriction obtained from current conservation using the Ward-Takahashi identity within the Bethe-Salpeter formalism. It is shown that this two-body relativistic current operator can be reduced to an effective one-body form. Applications of this method to nuclear few-body systems, relativistic quark systems, and hadronic resonance processes are discussed. The numerical size of the interaction current for the pion charge form factor is estimated.