L.J. van den Horn

Refraction in a pulsar magnetosphere - the effect of a variable emission height on pulse morphology

The Petrova (2000) model to calculate pulse profiles is extended to a variable emission height model to make it physically self-consistent. In this context variable means that the emission height is no longer considered to be the same for dierent magnetic field lines. The pulse profiles calculated using this new model seem to be less realistic due to a focusing e ect and cannot be used to fit (typical) multifrequency pulsar observations. Apart from the focusing eect the general morphology of pulse profiles is not greatly aected by introducing a variable emission height. Additional extensions of the model will be needed to be able to fit observations, and several suggestions are made.

Maximum entropy eddington factors in flux-limited neutrino diffusion

Abstract A neutrino transport scheme for use in dense stellar environments and collapsing stars is constructed. The maximum entropy principle is used to establish the general form of the angular neutrino distribution function. The two Lagrange multipliers introduced by this procedure are determined by using the flux-limited diffusion theory (FDT) of Levermore and Pomraning. In contrast to standard practice in radiation (photon) transport, the anisotropic scattering contribution is taken into account. Its inclusion leads to a modification of the Levermore-Pomraning approach. The transition from a multigroup to an energy-integrated transport scheme for FDT is investigated. In particular, the link to the two-fluid model of Cooperstein et al is made.

Neutrino diffusion in stellar collapse

We consider the diffusion flows of neutrinos in stellar collapse. The neutrino energy and number fluxes are driven by the gradients of temperature and chemical potential, and are characterized by four Rosseland mean free paths. We derive exact expressions for these Rosseland means, taking scattering and stimulated absorption of the neutrinos into account separately as well as in combination. The Rosseland means for the combined opacities constitute new analytical results. These exact expressions represent an improvement over previously published prescriptions.

Transport coefficients for the cosmological fluid during the lepton era

Abstract The coefficients of heat conductivity, diffusion, thermal diffusion, shear and bulk viscosity are evaluated for a non-degenerate (eν e ) mixture in which the particles interact in accordance with Weinberg-Salam model.

On gauge freedom in flux-limited diffusion theory

Abstract The approximation made in the derivation of the Levermore and Pomraning flux-limited diffusion theory (FDT) is investigated and resulting inconsistencies are noted. A gauge freedom in the central assumption is established. Modifications of the standard assumption are proposed and their consequences discussed. Incorporation of these modifications is shown to enhance the self-consistency of the LP method.

Relativistic kinetic theory of quantum systems: VII. Transport coefficients for (eve) and (evμ) mixtures

Abstract For (e v e ) and (e v μ ) binary mixtures the transport coefficients are evaluated as functions of the temperature and composition of the system. The particles are assumed to interact according to the Weinberg-Salam model. Results for the two mixtures are compared, and are contrasted to corresponding results obtained on the basis of a mean free path model.

Bulk viscosity of degenerate neutrinos

An expression for the bulk viscosity due to beta absorption in a system of neutrinos, neutrons, protons, and electrons is given. It generalizes a number of previously published results which are discussed and compared. It is stressed that the derivation is based on the condition of local beta equilibrium.

Transport properties of degenerate neutrinos and photons

Abstract Transport coefficients are presented for a mixture of neutrinos and nuclei, and for a photon-electron system. The expression are valid for arbitrary degeneracy of the massless component, and include generalizations of Weinbergs results for radiative heat conduction and viscosity.

Bulk viscosity of a reactive (νenpe−) system

Abstract The bulk viscosity arising from neutrino absorption by neutrons, and electron capture by protons, is calculated for arbitrary degeneracy of the leptons. These reactions are the primary processes determining the bulk viscosity of collapsing stellar cores. In this context the value found is of the order of 1024 g cm−1s−1.

Effects of neutrino degeneracy on the transport properties of presupernovae

Abstract Degeneracy of neutrinos undergoing coherent scattering by atomic nuclei inhibits their diffusion and enhances their thermal conduction and viscosity. For great degeneracy diffusion vanishes, while viscosity becomes independent of the temperature; the heat conductivity becomes independent of the neutrino chemical potential after attaining a maximum in the regime of intermediate degeneracy.