Light-cone Representation Research Articles

Spin structure of the pion in a light-cone representation

The spin structure of the pion is discussed by transforming the wave function for the pion in the naive quark model into a light-cone representation. It is shown that there are higher helicity (λ 1+λ 2=±1) states in the full light-cone wave function for the pion besides the ordinary helicity (λ 1+λ 2=0) component wave functions as a consequence from the Melosh rotation relating spin states in light-front dynamics and those in instantform dynamics. Some low energy properties of the pion, such as the electromagnetic form factor, the charged mean square radius, and the weak decay constant, could be interrelated in this representation with reasonable parameters.

Light-cone gauge Schwinger model

Nakawaki's Coulomb gauge solution to the Schwinger model is transformed to light-cone gauge. Various options for maintaining the gauge invariance necessary to satisfy the equations of motion are discussed. Satisfactory light-cone gauge solutions are found and are used to study light-cone quantization, the calculation of the dynamical operators and properties of the vacua in the light-cone representation. The solutions found here can be used to justify previous light-cone Tamm-Dancoff calculations performed by others.

The pion form factor in a light-cone representation

The Bethe-Salpeter equation is formulated on the light-cone for the composite quark-antiquark amplitude to study the pion form factor. A unified description of the pion form factor is obtained for all space-like momentum transfers, with a prediction that it will fall rapidly from the present experimental values to the asymptotic values by about 15 (GeV/ c) 2.

Soft-pion theorems and a light-cone quark model.

It is shown that in a light-cone representation of nucleons soft-pion theorems which are violated in instant-form quark models can be recovered with suitable choices of parameters of the model. Instantaneous terms must be included for the soft-pion limit. The proton form factors are fit up to {ital q}{sup 2}=3 (GeV/{ital c}){sup 2} in this model.

Gauge string fields from the light cone

We describe a method for deriving general gauge-invariant field theories from light-cone representations of the Poincaré algebra at x + = 0. By adding 2 commuting and 2 anticommuting dimensions, we obtain an enlarged symmetry group which includes the usual covariantly realized Poincaré group acting on D coordinates. The generators of the Lorentz subgroup which acts on the remaining, unphysical coordinates are used to define the gauge transformations. These generators are the BRST and anti-BRST operators, the SU(1,1) which defines the physical subspace, and generators which gauge away the unphysical coordinates. The free action, which is free of Nakanishi-Lautrup auxiliary fields, is just a δ function in these generators. The unphysical commuting coordinate can describe the string length as a gauge degree of freedom.