We study the motion of magnetized particles near a rotating black hole. The main result is that the spacetime curvature and electromagnetic field conspire to allow for the existence, inside the ergosphere, of stable circular orbits occupied by particles with negative total energy and angular momentum. Since these particles would never populate stable orbits were they not magnetized, a large binding energy is required to let them exist. A simple model of a magnetized belt in the ergosphere of a massive black hole with a strong magnetic field, shows that it can store a binding energy as high as 10 54 erg, an amount comparable with the energy detected in gamma ray bursts. Besides the above astrophysical considerations, this paper contains a formal deduction, from an appropriate Hamiltonian, of the equations of motion of a neutral and magnetized fluid made of spinless dust particles interacting with a magnetic field. This analysis does not appear to have been done before.

We propose a new approach to the study of spin-flip probability for massive Dirac neutrinos orbiting around a Schwarzschild black hole, recently considered by Dvornikov (2006 Int. J. Mod. Phys. 15 1017. Inspired by the paper by Papini and Lambiase (2002 Phys. Lett. A 294 175), we employ a reference frame comoving with the particle in the curved spacetime background. Using a suitable tetrad adapted to a comoving observer, we discuss the gravito-inertial effects (curvature plus spin rotation or Mashhoon effect) on the massive neutrino spin-flip probability. At variance with some recent claims, we find non-null results, in very good agreement with those obtained in [19], although through quite a different approach. Such results suggest a sort of competition between gravity and inertia. Taking into account the possible anomalous magnetic moment µ ν of a massive Dirac neutrino, we also briefly consider the interplay between gravito-inertial and magnetic effects, in the presence of some external strong magnetic field in the Schwarzschild geometry (which is believed to be a typical scenario in the case of Active Galactic Nuclei (AGN) or neutron stars). We find some evidence that the actual poor knowledge about the bounds on µ ν cannot rule out the possibility of some relevant competition between the two effects.

The nucleus 31 P has been studied in the 24 Mg( 16 O,2αp) reaction with a 70-MeV 16 O beam. A complex level scheme extended up to spins 17/2 + and 15/2 − , on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Two shell-model calculations have been performed to describe the experimental data, one by using the code ANTOINE in a valence space restricted to the sd shell, and the other by applying the Monte Carlo shell model in a valence space including the sd-fp shells. The latter calculation indicates that intruder excitations, involving the promotion of a T = 0 proton-neutron pair to the fp shell, play a dominant role in the structure of the positive-parity high-spin states of 31 P.