摘要:

I discuss several theoretical tools which are useful for analyzing perturbative and non-perturbative problems in quantum chromodynamics, including (a) the light-cone Fock expansion, (b) the effective charge&agr;V,(c) conformal symmetry, and (d) commensurate scale relations. Light-cone Fock-state wavefunctions encode the properties of a hadron in terms of its fundamental quark and gluon degrees of freedom. Given the proton’s light-cone wavefunctions, one can compute not only the quark and gluon distributions measured in deep inelastic lepton-proton scattering, but also the multi-parton correlations which control the distribution of particles in the proton fragmentation region and dynamical higher twist effects. Light-cone wavefunctions also provide a systematic framework for evaluating exclusive hadronic matrix elements, including timelike heavy hadron decay amplitudes and form factors. The&agr;Vcoupling, defined from the QCD heavy quark potential, provides a physical expansion parameter for perturbative QCD with an analytic dependence on the fermion masses which is now known to two-loop order. Conformal symmetry provides a template for QCD predictions, including relations between observables which are present even in a theory which is not scale invariant. Commensurate scale relations are perturbative QCD predictions based on conformal symmetry relating observable to observable at fixed relative scale. Such relations have no renormalization scale or scheme ambiguity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301659

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

I review ideas behind the light-front quantization of lattice gauge theories and give some illustrative results: [I] Transverse Lattice Gauge Theory; [II] Pure Glue; [III] Heavy Sources and Winding Modes; [IV] An Example—Large-NQCD in2+1Dimensions. (Very recent results for3+1-dimensions can be found in the presentation of B. van de Sande in the workshop proceedings.) ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301660

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A brief introduction to light front techniques is presented. This is followed by a review of recent attempts to perform realistic, relativistic nuclear physics with those techniques. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301661

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Light-cone quantization of gauge theories is discussed from two perspectives: as a calculational tool for representing hadrons as QCD bound-states of relativistic quarks and gluons, and as a novel method for simulating quantum field theory on a computer. A general non-perturbative method for numerically solving quantum field theories, ‘discretized light-cone quantization,’ is outlined. Both the bound-state spectrum and the corresponding relativistic wavefunctions can be obtained by matrix diagonalization and related techniques. Emphasis is put on the construction of the light-cone Fock basis and on how to reduce the many-body problem to an effective Hamiltonian. The usual divergences are avoided by cut-offs and subsequently removed by the renormalization group. For the first time, this program is carried out within a Hamiltonian approach, from the beginning to the end. Starting with the QCD-Lagrangian, a regularized effective interaction is derived and renormalized, ending up with an almost solvable integral equation. Its eigenvalues yield the mass spectrum of physical mesons, its eigenfunctions yield their wavefunctions including the higher Fock-space components. An approximate but analytic mass formula is derived for all physical mesons. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301662

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In these lectures we discuss the application of discrete light cone quantization (DLCQ) to supersymmetric field theories. We will see that it is possible to formulate DLCQ so that supersymmetry is exactly preserved in the discrete approximation. We call this formulation of DLCQ, SDLCQ and it combines the power of DLCQ with all of the beauty of supersymmetry. In these lecture we will review the application of SDLCQ to several interesting supersymmetric theories. We will discuss two dimensional theories with (1,1), (2,2) and (8,8) supersymmetry, zero modes, vacuum degeneracy, massless states, mass gaps, theories in higher dimensions, and the Maldacena conjecture among other subjects. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301663

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

It is shown that a consistent treatment of the axial anomaly leads to an explicit cancellation between the the infrared and ultraviolet contributions to the flavor singlet axial charge. This result is a consequence of the simultaneous crossing of the zero point energy and the ultraviolet cut-off by quark levels of defined chirality from the vacuum in the presence of gluon fields. Based on this consideration we give the arguments in favor of a large violation of the Ellis-Jaffe sum rule by predicting the vanishing of the flavor singlet axial chargegA0in a plausible scenario. From this result the value of the gluon polarization is estimated by using the Ku¨hn-Zakharov value for the matrix element of the axial anomaly. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301664

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The role of embedded states in the calculation of current matrix elements in light-front dynamics is discussed. As an example the current of a scalar boson with spin-1/2 constituents is calculated and numerical results are produced. They demonstrate the importance of the non-valence parts. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301665

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In these notes, the transverse (⊥) lattice approach is presented as a means to control thek+→0divergences in light-front QCD. Technical difficulties of both the canonical compact formulation as well as the non-compact formulation of the ⊥ lattice motivate the color-dielectric formulation, where the link fields are linearized. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301666

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We show that the method of “discretized light-cone quantization” (DLCQ) is in conflict with the principle of microcausality. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301667

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Calculations in a(3+1)-dimensional model indicate that Pauli-Villars regularization can be combined with discrete light-cone quantization (DLCQ) to solve at least some field theories nonperturbatively. Discrete momentum states of Pauli-Villars particles are included in the Fock basis to automatically generate needed counterterms; the resultant increase in basis size is found acceptable. The Lanczos algorithm is used to extract the lowest massive eigenstate and eigenvalue of the light-cone Hamiltonian, with basis sizes ranging up to 10.5 million. Each Fock-sector wave function is computed in this way, and from these one can obtain values for various quantities, such as average multiplicities and average momenta of constituents, structure functions, and a form-factor slope. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301668

出版商:AIP    

年代:1999

数据来源: AIP