Continuum Amplitudes Research Articles

Two-photon-exchange continuum contribution to elastic lepton-hadron scattering amplitudes.

We calculate the constant piece of the two-photon-exchange continuum contribution to the elastic lepton-hadron scattering amplitudes, which is dominant in a low-momentum-transfer expansion. We work it out on the basis of unitary, analyticity, Lorentz covariance, and gauge invariance. This constant piece coincides with the forward two-photon-exchange continuum amplitude. Its calculation opens a way to evaluate the asymmetry for positive- and negative-lepton--nucleus scattering at low-momentum transfer. The results are given in terms of the hadronic photoabsorption cross section, which is an experimental input in our calculation. Predictions of the amplitudes for leptons scattered by $^{4}\mathrm{He}$ and $^{12}\mathrm{C}$ are given.

Periodic amplitude variations in Jovian continuum radiation

An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both 5 and 10 hours. Contrary to a plausible initial idea, the continuum amplitudes are not organized by the position of the observer relative to the dense plasma sheet. Instead, there seem to be preferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clocklike modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude‐solar wind alignment to the amplitude of the continuum radiation implies that the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.

Locally complex distortions of the energy spectrum in the calculation of scattering amplitudes and photoionization cross sections.

We demonstrate that the array of techniques employing complex basis functions, which have been broadly applied in the calculation of resonance positions and lifetimes, can also be used, with appropriate modification, in the practical computation of photoionization cross sections and nonresonant scattering amplitudes. We illustrate a procedure with which controlled complex distortions over a localized region of the energy spectrum can be realized in a finite basis-set calculation. This technique is used to directly obtain scattering amplitudes for potentials which are not exponentially bounded at large distances, in contrast to complex scaling techniques which have been shown to be divergent in such cases. Four numerical examples are presented to exhibit the utility of the local complex distortion approach in calculations of photoionization cross sections and scattering amplitudes. We also discuss this approach in the context of variational principles for continuum amplitudes and in the context of applications to many-electron systems.