B. D. Keister

Baryon current matrix elements in a light-front framework

Current matrix elements and observables for electro- and photo-excitation of baryons from the nucleon are studied in a light-front framework. Relativistic effects are estimated by comparison to a nonrelativistic model, where the authors use simple basis states to represent the baryon wavefunctions. Sizeable relativistic effects are found for certain transitions, for example, to radial excitations such as that conventionally used to describe to the Roper resonance. A systematic study shows that the violation of rotational covariance of the baryon transition matrix elements stemming from the use of one-body currents is generally small.

Causality in dense matter

The possibility of noncausal signal propagation is examined for various theories of dense matter. This investigation requires a discussion of definitions of causality, together with interpretations of spacetime position. Specific examples are used to illustrate the satisfaction or violation of causality in realistic calculations. \textcopyright{} 1996 The American Physical Society.

Useful Bases for Problems in Nuclear and Particle Physics

A set of exactly computable orthonormal basis functions that are useful in computations involving constituent quarks is presented. These basis functions are distinguished by the property that they fall off algebraically in momentum space and can be exactly Fourier?Bessel transformed. The configuration space functions are associated Laguerre polynomials multiplied by an exponential weight, and their Fourier?Bessel transforms can be expressed in terms of Jacobi polynomials in ?2/(k2+ ?2). A simple model of a meson containing a confined quark-antiquark pair shows that this basis is much better at describing the high-momentum properties of the wave function than the harmonic-oscillator basis.

Relativistic dynamics and the deuteron axial form factor

Matrix elements of the deuteron axial current are calculated in the covariant spectator scheme of Gross, and compared to a corresponding calculation using light-front dynamics. The results confirm the dominant role in both approaches of the deuteron D state in observable effects beyond the nonrelativistic limit. {copyright} {ital 1997} {ital The American Physical Society}

Baryon resonance electroexcitation in a light‐cone model

Baryon resonance photo‐ and electroexcitation current matrix elements and helicity amplitudes are studied in a model based on light‐front Hamiltonian dynamics.