arXiv subjects

Ulrich D. Jentschura

Publications and source records attributed to Ulrich D. Jentschura.

60 records · Page 4Linked to original sources

arXiv2003

Extrapolation of the Zalpha-Expansion and Two--Loop Bound--State Energy Shifts

Quantum electrodynamic (QED) effects that shift the binding energies of hydrogenic energy levels have been expressed in terms of a semi-analytic expansion in powers of Zalpha and ln[(Zalpha)^{-2}], where Z is the nuclear charge number and alpha is the fine-structure constant. For many QED effects, numerical data are available in the domain of high Z where the Zalpha expansion fails. In this Letter, we demonstrate that it is possible, within certain limits of accuracy, to extrapolate the Zalpha-expansion from the low-Z to the high-Z domain. We also review two-loop self-energy effects and provide an estimate for the problematic nonlogarithmic coefficient B_60.

hep-ph↗

arXiv2003

Radiative energy shifts induced by local potentials

We study a specific correction to the Bethe logarithm induced by potentials which are proportional to a Dirac-delta function in coordinate space ("local potentials"). Corrections of this type occur naturally in the calculation of various self-energy corrections to the energy of bound states. Examples include logarithmic higher-order binding corrections to the two-loop self-energy, vacuum-polarization induced corrections to the self-energy and radiative corrections induced by the finite size of the nucleus. We obtain results for excited S and P states and find that the dependence of the corrections on the principal quantum number is remarkable. For the ground state, we find a small modification as compared to previously reported results. Our results are based on mathematical techniques for the treatment of quantum electrodynamic bound states discussed previously in [J. Phys. A 35 (2002) 1927, hep-ph/0111084].

hep-ph↗

arXiv2003

Asymptotic properties of self-energy coefficients

We investigate the asymptotic properties of higher-order binding corrections to the one-loop self-energy of excited states in atomic hydrogen. We evaluate the historically problematic A60 coefficient for all P states with principal quantum numbers n <= 7 and D states with n <= 8 and find that a satisfactory representation of the n-dependence of the coefficients requires a three-parameter fit. For the high-energy contribution to A60, we find exact formulas. The results obtained are relevant for the interpretation of high-precision laser spectrocopic measurements.

physics.atom-ph↗

arXiv2002

Nonresonant effects in one- and two-photon transitions

We investigate nonresonant contributions to resonant Rayleigh scattering cross sections of atoms. The problematic nonresonant contributions set a limit to the accuracy to which atomic spectra determine energy levels. We discuss the off-resonance effects in one-photon transitions. We also show that off-resonance contributions for the 1S-2S two-photon transition in atomic hydrogen are negligible at current and projected levels of experimental accuracy. The possibility of a differential measurement for the detection of off-resonance effects in one-photon transitions in atomic hydrogen is discussed.

physics.atom-ph↗

arXiv2002

Two-Loop Self-Energy Corrections to the Fine-Structure

We investigate two-loop higher-order binding corrections to the fine structure, which contribute to the spin-dependent part of the Lamb shift. Our calculation focuses on the so-called ``two-loop self-energy'' involving two virtual closed photon loops. For bound states, this correction has proven to be notoriously difficult to evaluate. The calculation of the binding corrections to the bound-state two-loop self-energy is simplified by a separate treatment of hard and soft virtual photons. The two photon-energy scales are matched at the end of the calculation. We explain the significance of the mathematical methods employed in the calculation in a more general context, and present results for the fine-structure difference of the two-loop self-energy through the order of $α^8$.

hep-ph↗

arXiv2001

QED Effective Action Revisited

The derivation of a convergent series representation for the quantum electrodynamic effective action obtained by two of us (S.R.V. and D.R.L.) in [Can. J. Phys. vol. 71, p. 389 (1993)] is reexamined. We present more details of our original derivation. Moreover, we discuss the relation of the electric-magnetic duality to the integral representation for the effective action, and we consider the application of nonlinear convergence acceleration techniques which permit the efficient and reliable numerical evaluation of the quantum correction to the Maxwell Lagrangian.

hep-th↗