3,826 research outputs found
Neutrino asymmetry in general relativistic rotating radiative stars
Neutrino asymmetry in general relativistic radiative spacetime exterior to
spinning stars is investigating by making use of Newmann-Penrose (NP) spin
coefficient formalism. It is shown that neutrino current depends on the
direction of rotation of the star. The solution is obtained in test field
approximation where the neutrinos do not generate gravitational fields.Comment: Latex fil
A teleparallel effective geometry for Einstein's unified field theory
Riemannian and teleparallel geometrical approaches to the investigation of
Maxwell electrodynamics shown that a unified field theory of gravitation and
electromagnetism a la Einstein can be obtained from a stationary metric. This
idea contrasts with the recently proposed pre-metric electrodynamics by Hehl
and Obukhov. In the teleparallel case the definition of the electric field is
obtained straightforward from the spacetime metric and the orthonormal basis
frame of teleparallelism. In this case the only nonvanishing component of
Cartan torsion is defined as the effective electric field. In this approach the
gravitational potentials or metric coefficients are expressed in terms of the
effective or analogous electric and magnetic potentials. Thefore the Maxwell
equations in vacuum can be obtained by derivation of this electric field
definition as usual. In the Riemannian case we consider an electrostatic
spacetime where the Einstein equations in vacuum in the approximation of linear
fields. The constraint of Einstein equations in vacuum are shown to lead or to
the Coulomb equation or to a singular behaviour on the metric which would
represent a kind of effective electrodynamic black hole event horizon.Comment: Latex fil
Cosmological Background torsion limits from Lorentz violation
Cosmological limits on Lorentz invariance breaking in Chern-Simons
electrodynamics are used to place limits on torsion.
Birefrigence phenomena is discussed by using extending the propagation equation
to Riemann-Cartan spacetimes instead of treating it in purely Riemannian
spaces. The parameter of Lorentz violation is shown to be proportional to the
axial torsion vector which allows us to place a limit on cosmological
background torsion from the Lorentz violation constraint which is given by where is the axial torsion
vector.Comment: Latex fil
Gravitational torsion kinks and thick domain walls
The dynamics of a gravitational torsion kink as a plane symmetric thick
domain wall solution of Einstein-Cartan (EC) field equation is given. The
spin-torsion energy has to be as high as the gravitational kink potential
otherwise torsion will not contribute as an appreciable effect to domain
wall.Cartan torsion also contributes to the orthonal pressure of the domain
wall.Comment: 5 pages late
Dynamos driven by poloidal flows in untwisted, curved and flat Riemannian diffusive flux tubes
Recently Vishik anti-fast dynamo theorem, has been tested against
non-stretching flux tubes [Phys Plasmas 15 (2008)]. In this paper, another
anti-dynamo theorem, called Cowling's theorem, which states that axisymmetric
magnetic fields cannot support dynamo action, is carefully tested against thick
tubular and curved Riemannian untwisted flows, as well as thin flux tubes in
diffusive and diffusionless media. In the non-diffusive media the Cowling's
theorem is not violated in thin Riemann-flat untwisted flux tubes, where the
Frenet curvature is negative. Nevertheless the diffusion action in the thin
flux tube leads to a a dynamo action driven by poloidal flows as shown by Love
and Gubbins (Geophysical Res.) in the context of geodynamos. Actually it is
shown that a slow dynamo action is obtained. In this case the Frenet and
Riemann curvature still vanishes. In the case of magnetic filaments in
diffusive media dynamo action is obtained when the Frenet scalar curvature is
negative. Since the Riemann curvature tensor can be expressed in terms of the
Frenet curvature of the magnetic flux tube axis, this result can be analogous
to a recent result obtained by Chicone, Latushkin and Smith, which states that
geodesic curvature in compact Riemannian manifolds can drive dynamo action in
the manifold. It is also shown that in absence of diffusion, magnetic energy
does not grow but magnetic toroidal magnetic field can be generated by the
poloidal field, what is called a plasma dynamo
Torsion effects on vortex filaments and Hasimoto soliton transformation in magnetars
The role played by torsion of magnetic vortex line curves or filaments, in
the equilibrium state of magnetars is investigated. When the magnetars
equilibrium equations are written in terms Frenet-Serret frame it is shown that
in regions of the magnetic star where the Frenet torsion is constant it induces
an oscillation in the vortex filaments. By solving the magnetar equilibrium
equation we shown the this behaviour also appears in the magnetic field. The
first derivative of the gravitational potential with respect to the arc lenght
of the vortex filament is shown to coincide with the Hasimoto soliton
transformation of the Schroedinger equation for the constant torsion.Comment: Latex fil
Torsion Strings inside Static Black Holes in Teleparallel Gravity
Cosmic strings inside Schwarzschild black holes in teleparallel gravity are
considered.Torsion flux inside the black hole is compute like a torsion vortex
on a superfluid.Since some components of torsion are singular on Schwarzschild
horizon and others remain finite we compute a torsion invariant to decide
whether the torsion is singular and where torsion singularities located.It is
found out that as in the curvature case of Einstein's black hole the event
horizon is not a mere coordinate singularity for torsion although a true
torsion singularity is found at the center of the teleparallel black
hole.Torsion flux vanishes along the cosmic string itself.It is shown from
Cartan equation in differential forms that the spins inside the black hole are
polarized along the torsion string.Torsion string seems to be confined inside
the black hole.Comment: Latex fil
Spin polarised particles in Goedel world
The motion of classical test spinning particles in Godel universe in the
realm of Einstein's General Relativity (GR) is investigated by making use of
Killing conserved currents. We consider three distinct cases of motion of
spinning particles polarized along the three distinct axes of the anisotropic
metric. It is shown that in the case the spin is polarised along the
y-direction the minimum energy of the motion is attained for only for spinless
particles while the other two directions the minimum energy is obtained for
spinning particles. The continuos energy spectrum is also computed.Comment: Latex fil
Non-Riemannian effective spacetime effects on Hawking radiation in superfluids
Riemannian effective spacetime description of Hawking radiation in
superfluids is extended to non-Riemannian effective spacetime. An example is
given of non-Riemannian effective geometry of the rotational motion of the
superfluid vacuum around the vortex where the effective spacetime Cartan
torsion can be associated to the Hawking giving rise to a physical
interpretation of effective torsion recently introduced in the literature in
the form of an acoustic torsion in superfluid (PRD-70(2004),064004).
Curvature and torsion singularities of this fermionic superfluid are
investigated. This Lense-Thirring effective metric, representing the superfluid
vacuum in rotational motion, is shown not support Hawking radiation when the
isotropic is restored at far distances from the vortex axis. Hawking
radiation can be expressed also in topological solitons (moving domain walls)
in fermionic superfluids in non-Riemannian (teleparallel) dimensional
effective spacetime. A teleparallel solution is proposed where the
quasiparticle speed is determined from the teleparallel geometry.Comment: Latex fil
Spin-Polarised Cylinders and Torsion Balances to test Einstein-Cartan Gravity?
Spin-Polarised cylinders with and without axial magnetic fields are obtained
as particular families of solutions of Einstein-Cartan gravity (EC).The first
solution represents a spin-polarised cylinder in teleparallel gravity.The
second solution is a magnetized solution representing a spin-polarised cylinder
where the magnetic fields and spins are distributed along the infinite axis of
the cylinder.Altough it seems that the first solution is less realist than the
second it could be obtained by shielding the magnetic fields with a
superconductor.The second solution is computed by taking into account the
Ritter et al. experiment with the test spin-polarized mass to test spin
dependent forces.Ritter experiment deals with a test mass with spin
polarized electrons which leads to a spin density of .Comment: latex fil
- …