8,627 research outputs found
Model for an optically thick torus in local thermodynamic equilibrium around a black hole
We propose a simple model for an optically thick radiative torus in local
thermodynamic equilibrium around a Kerr black hole. The hydrodynamics
structure, which is not affected by the radiation field, is the same as for the
so--called polish doughnuts. Under the assumption of isentropic fluid and
polytropic equation of state, a simple stationary and axisymmetric solution to
the relativistic radiation hydrodynamics equations is possible, for which the
temperature of the torus scales like the specific enthalpy. The astrophysical
relevance of the model is briefly discussed.Comment: With updated bibliographyc informatio
Systematic uncertainties in the precise determination of the strangeness magnetic moment of the nucleon
Systematic uncertainties in the recent precise determination of the
strangeness magnetic moment of the nucleon are identified and quantified. In
summary, G_M^s = -0.046 \pm 0.019 \mu_N.Comment: Invited presentation at PAVI '04, International Workshop on Parity
Violation and Hadronic Structure, Laboratoire de Physique Subatomique et de
Cosmologie, Grenoble, France, June 8-11, 2004. 7 pages, 16 figure
Very High Order \PNM Schemes on Unstructured Meshes for the Resistive Relativistic MHD Equations
In this paper we propose the first better than second order accurate method
in space and time for the numerical solution of the resistive relativistic
magnetohydrodynamics (RRMHD) equations on unstructured meshes in multiple space
dimensions. The nonlinear system under consideration is purely hyperbolic and
contains a source term, the one for the evolution of the electric field, that
becomes stiff for low values of the resistivity. For the spatial discretization
we propose to use high order \PNM schemes as introduced in \cite{Dumbser2008}
for hyperbolic conservation laws and a high order accurate unsplit time
discretization is achieved using the element-local space-time discontinuous
Galerkin approach proposed in \cite{DumbserEnauxToro} for one-dimensional
balance laws with stiff source terms. The divergence free character of the
magnetic field is accounted for through the divergence cleaning procedure of
Dedner et al. \cite{Dedneretal}. To validate our high order method we first
solve some numerical test cases for which exact analytical reference solutions
are known and we also show numerical convergence studies in the stiff limit of
the RRMHD equations using \PNM schemes from third to fifth order of accuracy
in space and time. We also present some applications with shock waves such as a
classical shock tube problem with different values for the conductivity as well
as a relativistic MHD rotor problem and the relativistic equivalent of the
Orszag-Tang vortex problem. We have verified that the proposed method can
handle equally well the resistive regime and the stiff limit of ideal
relativistic MHD. For these reasons it provides a powerful tool for
relativistic astrophysical simulations involving the appearance of magnetic
reconnection.Comment: 24 pages, 6 figures, submitted to JC
Quasi-optimal nonconforming methods for symmetric elliptic problems. I -- Abstract theory
We consider nonconforming methods for symmetric elliptic problems and
characterize their quasi-optimality in terms of suitable notions of stability
and consistency. The quasi-optimality constant is determined and the possible
impact of nonconformity on its size is quantified by means of two alternative
consistency measures. Identifying the structure of quasi-optimal methods, we
show that their construction reduces to the choice of suitable linear operators
mapping discrete functions to conforming ones. Such smoothing operators are
devised in the forthcoming parts of this work for various finite element
spaces
Hybrid Meson Spectrum from the FLIC action
The spectral properties of hybrid meson interpolating fields are
investigated. The quantum numbers of the meson are carried by smeared-source
fermion operators and highly-improved chromo-electric and -magnetic field
operators composed with APE-smeared links. The effective masses of standard and
hybrid operators indicate that the ground state meson is effectively isolated
using both standard and hybrid interpolating fields. Focus is placed on
interpolating fields in which the large spinor components of the quark and
antiquark fields are merged. In particular, the effective mass of the exotic
meson is reported. Further, we report some values for excited mesonic
states using a variational process.Comment: Talk given by A.G Williams at Workshop on Lattice Hadron Physics,
Cairns, Queensland, Australia, July 200
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