Heavy-quark mesons in the diabatic approach: string breaking and the quarkoniumlike spectrum

The Born-Oppenheimer approximation provides a description of heavy-quark mesons firmly based on lattice QCD, but its validity is limited to the lightest states lying far below the first open-flavour meson-meson threshold. This limitation can be overcome in the diabatic framework, a formalism first introduced in molecular physics, where the dynamics is encoded in a potential matrix whose elements can be derived from unquenched lattice QCD studies of string breaking. The off-diagonal elements of the potential matrix provide interaction between heavy quark-antiquark and meson-meson pairs, from which the mixing of quarkonium states with molecular components and the OZI-allowed strong decay widths are directly calculated. This allows for a QCD-based unified description of conventional quarkonium and unconventional mesons containing quark-antiquark and meson-meson components, what has proved to be successful for charmoniumlike and bottomoniumlike resonances.

Back to the roots: the concepts of force and energy

The concepts of force and energy are analyzed in the context of state and process equations. In chronological order, the application of the cause-effect principle in process equations is studied in mechanics, thermodynamics, special relativity, general relativity, and quantum theory. The differences in the fundamental approaches to nature and the significance of a consistent physical interpretation of formulas and state variables are emphasized. It is shown that the first origins for the crisis of modern theoretical physics are to be found in the concepts of force and energy in mechanics, which partly violate the cause-effect principle. This affects all theories based on mechanics and underlines their historical conditionality. The systematic application of driving forces and the cause-effect principle in process equations suggests a return to causal realistic physics. It meets the wave character of matter, is compatible with the experiment, and allows a unified description of interaction.

Open-source implementation of the discrete-dipole approximation for a scatterer in an absorbing host medium

Theoretical description of light scattering by single particles is a well-developed field, but most of it applies to particles located in vacuum or non-absorbing host medium. Although the case of absorbing host medium has also been discussed in literature, a complete description and unambiguous definition of scattering quantities are still lacking. Similar situation is for simulation methods – some computer codes exist, but their choice is very limited, compared to the case of vacuum. Here we describe the extension of the popular open-source code ADDA to support the absorbing host medium. It is based on the discrete dipole approximation and is, thus, applicable to particles with arbitrary shape and internal structure. We performed test simulations for spheres and compared them with that using the Lorenz-Mie theory. Moreover, we developed a unified description of the energy budget for scattering by a particle in a weakly absorbing host medium, relating all existing local (expressed as volume integrals over scatterer volume) and far-field scattering quantities.