Light-cone Physics Research Articles

Pion wave function from lattice QCD vs. chiral quark models

We analyze the equal-time Bethe–Salpeter quark wave function of the pion obtained from a quenched lattice QCD calculation with delocalized quark interpolators. We find that the result agrees remarkably well with the predictions of the Nambu–Jona-Lasinio model in all channels. We choose the quenched lattice QCD since it is closer to the large- N c limit of Nambu–Jona-Lasinio model. We also show how transversity information, relevant for the light-cone physics, can be obtained from our equal-time rest-frame lattice calculations.

Physics at the light-front

The light-front representation of quantum chromodynamics provides a frame-independent, quantum-mechanical representation of hadrons at the amplitude level, capable of encoding their multi-quark, hidden-color and gluon momentum, helicity, and flavor correlations in the form of universal process-independent hadron wavefunctions. The universality and frame-independence of the LCWF's thus allow a profound connection between diffractive dissociation, hard scattering exclusive processes such as elastic form factors, two-photon reactions, and heavy hadron decays. In this concluding talk of the ECT* International Conference On Light-Cone Physics: Particles And Strings (Trento 2001), I review recent calculations and new applications of light-front wavefunctions in QCD and other theories. I also review the distinction between the structure functions measured in deep inelastic lepton scattering and the quark distributions determined from light-front wavefunctions.

Matrices on a point as the theory of everything

It is shown that the world line can be eliminated in the matrix quantum mechanics conjectured by Banks, Fischler, Shenker, and Susskind to describe the light-cone physics of M theory. The resulting matrix model has a form that suggests origins in the reduction to a point of a Yang-Mills theory. The reduction of the Nishino-Sezgin (10+2)-dimensional supersymmetric Yang-Mills theory to a point gives a matrix model with the appropriate features: Lorentz invariance in $9+1$ dimensions, supersymmetry, and the correct number of physical degrees of freedom.

Kindergarten parton model

Theory of Lepton-Hadron Processes at High Energies: Partons, Scale Invariance, and Light-Cone Physics. (Oxford Studies in Physics.) By Roy Probir. Pp. x + 172. (Clarendon: Oxford; Oxford University Press: London; February 1975.) £6.

Light-cone physics, current algebra and PCAC

It is shown that the light-cone operator expansion of the product of two SU(3) ⊗ SU(3) currents or divergences, the requirement of maximal analyticity of the second kind, and the mathematical method of analytic continuation can be used to shed light on the validity and meaning of the Ward-Takahashi identities, of the Bjorken-Johnson-Low limit and in general of sum rules derived from current algebra either at equal time or on the light cone. In particular we give a definite content to the PCAC hypothesis in terms of the ‘dimension’ of the axial divergence and suggest some specific values for this ‘dimension’. It is also shown that the requirement of maximal analyticity of the second kind and gauge invariance impose a non-trivial condition on the Cornwall-Corrigan-Norton sum rule.

Theory of Lepton–Hadron Processes at High Energies: Partons, Scale Invariance, and Light Cone Physics

Probir Roy London: Oxford University Press 1975 pp x + 172 price £6 This book is divided into three sections, one on each of the topics in the subtitle which are treated at an introductory level suitable for a graduate student. Although better coverage of much of the material at a deeper level can be found in the literature (eg in Feynman's book and the lectures by Coleman and by Ellis and Jaffe, all referred to in the bibliography), the best sources are often hard to find and, in any case, I know of no unified treatment of these topics.

Conformal invariance, singular bilocal operators and scaling in some deep inelastic-scattering and annihilation processes

Since the beginning of light-cone physics, there has been a wide search for a concrete machinery to explore the potentiality of such a scheme. One of the most handy and mathematically sound is the idea of eonformal invarianee, the other available methods being the l ight-cone per turbat ion theory, the algebra of bilocM opel'ators and so on. For some inherent sol idi tar i ty of the extended Poincar6 algebra i t is possible to search for some ye t unknown clues observed in recent experimental findings of SLAC-DESY accelerators. One of the most confusing problems is the proper character of the bilocal operators measured in such deep inelastic processes. Such questions have a l ready been dealt wi th by JAc~:IW and WALTZ (1) and by SNITZ]~R (2), with the help of per turbat ion theory on r light-cone in the quark-gluon model. In this note we have analysed such problem with the machinery of conformal invariance utilizing the techniques of F ] ~ A ~ A et al. (a). In the following we will discuss two different inelastic lepr processes, e + e ~ = + a n y t h i n g (as a pro to type of annihilation process) and e -p -> e = + a n y t h i n g , serving as a case of deep inelastic-scatter . ing process. Two different characters of the biloeal operators (occurring as the coefficients of leading singularities on the light-cone) are exhibited. To begin with, we consider the LSZ form of the ampli tude for e§ = + a n y t h i n g which reads

Errata and Addenda: Light-Cone Analysis of Virtual Processes

Errors in a recent paper by the authors are corrected. Previously omitted terms which contribute to an effective Lagrangian are evaluated. The role of divergence conditions in light-cone physics is emphasized.

Light-cone physics. Problems and perspectives

I have tried to give a concise summary of the various directions in which research has proceeded in the field of LC physics. For space reasons no details have been given of the several applications mentioned in Sect. 3 and 4. However this can be easily filled in by resorting to the rich existing literature, which testifies the widespread interest in present-day theoretical physics for the approach described in this talk.

Light-cone physics and duality

In this paper we make an attempt to grasp some features of hadron physics in terms of light-cone properties. Hadrons are considered, in the light-cone asymptotism, as aggregates of free massless quarks, aligned on the same direction (collinearity). The hadron states are classified by a representation of anO 2.1 algebra, constructed from the generators of the conformal group. Deep inelastic structure functions are evaluated and discussed. Analogies between duality and light-cone physics are stressed.