Neutral baryonic systems with strangeness

We review the status as regards to the existence of three- and four-body bound states made of neutrons and [Formula: see text] hyperons. For interesting cases, the coupling to neutral baryonic systems made of charged particles of different strangeness has been addressed. There are strong arguments showing that the [Formula: see text] system has no bound states. [Formula: see text] strong stable states are not favored by our current knowledge of the strangeness [Formula: see text] and [Formula: see text] baryon–baryon interactions. However, a possible [Formula: see text] quasibound state decaying to [Formula: see text] might exist in nature. Similarly, there is a broad agreement about the nonexistence of [Formula: see text] bound states. However, the coupling to [Formula: see text] states opens the door to a resonance above the [Formula: see text] threshold.

Quasibound states of the Dirac field in Schwarzschild and Reissner–Nordström black hole backgrounds

In this paper, we study the existence of (quasi)bound states in two spacetime geometries describing Schwarzschild and Reissner–Nordström black holes. For obtaining these types of states, we search for discrete quantum modes of the massive Dirac equation in the two geometries. After imposing the quantization condition, an analytical expression for the energy of the ground states is derived. The energy of higher states is then obtained numerically. For very small values of the black hole mass M, we compare the energy of the Reissner–Nordström black hole quasibound state with the Dirac–Coulomb energy and we have found the two to be in good agreement.

Symmetry of molecular Rydberg states revealed by XUV transient absorption spectroscopy

Transient absorption spectroscopy is utilized extensively for measurements of bound- and quasibound-state dynamics of atoms and molecules. The extension of this technique into the extreme ultraviolet (XUV) region with attosecond pulses has the potential to attain unprecedented time resolution. Here we apply this technique to aligned-in-space molecules. The XUV pulses are much shorter than the time during which the molecules remain aligned, typically $$<$$<100 fs. However, transient absorption is not an instantaneous probe, because long-lived coherences re-emit for picoseconds to nanoseconds. Due to dephasing of the rotational wavepacket, it is not clear if these coherences will be evident in the absorption spectrum, and whether the properties of the initial excitations will be preserved. We studied Rydberg states of N$${}_{2}$$2 and O$${}_{2}$$2 from 12 to 23 eV. We were able to determine the polarization direction of the electronic transitions, and hence identify the symmetry of the final states.

THE γp → K0Σ+ PHOTOPRODUCTION REACTION

The photoproduction reaction γp → K0Σ+ was investigated with the CBELSA/TAPS experiment at the electron accelerator facility ELSA of the University of Bonn. A pronounced structure in the cross section was found at the K* threshold. There are indications that this may be associated with the formation of a K*-hyperon quasibound state below the K* threshold. The very first measurements of the photon beam asymmetry in the studied reaction channel are presented and their impact is discussed.