One-step model of photoemission for non-local potentials

The one-step model of valence-band photoemission and inverse photoemission from single-crystal surfaces is reformulated for generalized (non-local, complex and energy-dependent) potentials. Thereby, it becomes possible to account for self-energy corrections taken from many-body electronic-structure calculations. The original formulation due to Pendry and co-workers employs the KKR multiple-scattering theory for the calculation of the initial state. This prevents a straightforward generalization of the one-step model to non-local potentials. We therefore consider the Dyson equation which is set up within a muffin-tin-orbitals representation as an alternative to obtain the initial-state Green function. This approach requires a revision of the transition-matrix elements which is carried out in detail. The final state is considered as a time-reversed LEED state as usual. The proposed generalization of the one-step model allows to distinguish between the bare photocurrent reflecting the (quasi-particle) band structure and the secondary effects due to the (dipole) selection rules and due to the wave-vector and energy dependence of the transition-matrix elements.Comment: Revtex, 20 pages, no figures, phys. stat. sol. (b) 203 (in press

Direct URCA Processes in Supernovae and Accretion Disks with Arbitrary Magnetic Field

An effect of a magnetic field of an arbitrary strength on the beta-decay and reactions related with it by the crossing symmetry (the beta-processes) in supernovae and accretion disks around black holes is analyzed. Rates of the beta-processes and the energy and momentum transfered through them to an optically transparent matter are calculated. It is shown that the macroscopic momentum transferred to the medium increases linearly with the magnetic field strength and can substantially affect the dynamics of supernovae and accretion disks especially when a matter inside is degenerate. It is also demonstrated that the rates of the beta-processes and the energy deposition in these reactions for the magnetic field strength $B \lesssim 10^{15}$ G, which is assumed to be typical in supernovae and accretion disks, are lower than in the absence of the field. This suppression is more pronounced for reactions with neutrinos.Comment: 10 pages, 5 figure

Electron-positron pairs in hot plasma of accretion column in bright X-ray pulsars

The luminosity of X-ray pulsars powered by accretion onto magnetized neutron stars covers a wide range over a few orders of magnitude. The brightest X-ray pulsars recently discovered as pulsating ultraluminous X-ray sources reach accretion luminosity above $10^{40}\,{\rm erg\,s^{-1}}$ which exceeds the Eddington value more than by a factor of ten. Most of the energy is released within small regions in the vicinity of magnetic poles of accreting neutron star - in accretion columns. Because of the extreme energy release within a small volume accretion columns of bright X-ray pulsars are ones of the hottest places in the Universe, where the internal temperature can exceed 100 keV. Under these conditions, the processes of creation and annihilation of electron-positron pairs can be influential but have been largely neglected in theoretical models of accretion columns. In this letter, we investigate properties of a gas of electron-positron pairs under physical conditions typical for accretion columns. We argue that the process of pairs creation can crucially influence both the dynamics of the accretion process and internal structure of accretion column limiting its internal temperature, dropping the local Eddington flux and increasing the gas pressure.Comment: 5 pages, 5 figures, accepted for publication in MNRAS Letter