Magnetic dominance of axion electrodynamics: photon capture effect and anisotropy of Coulomb potential

For magnetic fields larger than the characteristic scale linked to axion-electrodynamics, quantum vacuum fluctuations due to axion-like fields can dominate over those associated with the electron-positron fields. This conjecture is explored by investigating both the axion-modified photon capture by a strong magnetic field and the Coulomb potential of a static pointlike charge. We show that in magnetic fields characteristic of neutron stars $$\sim 10^{13}$$ ∼ 10 13 –$$10^{15}\;\mathrm{G}$$ 10 15 G , the capture of gamma photons prior to the production of a pair can prevent the existence of an electron-positron plasma, essential for explaining the pulsar radiation mechanism. This incompatibility is used to limit the axion parameter space. Our bounds improve existing outcomes in the region of mass $$m\sim 10^{-10}$$ m ∼ 10 - 10 –$$10^{-5}\;{\mathrm{eV}}$$ 10 - 5 eV . The effect of capture, known in QED as relating to gamma-quanta, is extended in axion electrodynamics to include X-ray photons with the result that a specially polarized part of the heat radiation from the surface is canalized along the magnetic field. Besides, we find that in the regime in which the dominance takes place, the running QED coupling depends on the field strength and the modified Coulomb potential is of Yukawa-type in the direction perpendicular to the magnetic field at distances much smaller than the axion Compton wavelength, while along the field it follows approximately the Coulomb law at any length scale. Despite the Coulomb singularity manifested in the latter case, we argue that the ground-state energy of a non-relativistic hydrogen atom placed in a strong magnetic field turns out to be bounded due to the nonrenormalizable feature of axion-electrodynamics.

Peculiarities of Matrix-Element Calculations with Few Coulomb Functions for Particles’ Scattering Processes

Specific features of the matrix-element calculations in the momentum-space representation are discussed for the single ionization of the He atom by fast proton impact in the case when the Coulomb interactions of all three charged fragments in the final state are taken into account. It is shown that a “soft” smoothing of the Coulomb singularity does not affect the accuracy of the calculations in a certain region of the smoothing parameter values.

Singularity avoidance, lattices, and quantum gravity

An ingredient in recent discussions of curvature singularity avoidance in quantum gravity is the “inverse scale factor” operator in quantum cosmology, and its generalizations to field theoretic models such as scalar-field collapse in spherical symmetry. I describe a general lattice origin of this idea, and show how it applies to the Coulomb singularity in quantum mechanics. The example demonstrates that a discretized Schrodinger equation is computationally equivalent to the so-called polymer quantization derived loop quantum gravity. This applies also to lattice discretized forms of the Wheeler–deWitt equation.PACS Nos.: 04.60.–m, 04.60.Ds, 04.70.Dy