15,591 research outputs found
Axisymmetric Stationary Solutions as Harmonic Maps
We present a method for generating exact solutions of Einstein equations in
vacuum using harmonic maps, when the spacetime possesses two commutating
Killing vectors. This method consists in writing the axisymmetric stationry
Einstein equations in vacuum as a harmonic map which belongs to the group
SL(2,R), and decomposing it in its harmonic "submaps". This method provides a
natural classification of the solutions in classes (Weil's class, Lewis' class
etc).Comment: 17 TeX pages, one table,( CINVESTAV- preprint 12/93
Scalar Field Dark Matter mass model and evolution of rotation curves for Lsb galaxies
We study the evolution of gas rotation curves within the scalar field dark
matter (SFDM) model. In this model the galactic haloes are astronomical
Bose-Einstein Condensate drops of scalar field. These haloes are characterized
by a constant-density core and are consistent with observed rotation curves of
dark matter dominated galaxies, a missing feature in CDM haloes resulting from
DM-only simulations. We add the baryonic component to the SFDM haloes and
simulate the evolution of the dark matter tracer in a set of grid-based
hydrodynamic simulations aimed to analyse the evolution of the rotation curves
and the gas density distribution in the case of dark matter dominated galaxies.
Previous works had found that when considering an exact analytic solution for a
static SF configuration, the free parameters of the model allows for good fits
to the rotation curves, we confirm that in our simulations but now taking into
account the evolution of the baryonic component in a static dark matter and
stellar disk potential. Including live gas is a step forward from the previous
work using SFDM, as for example, the rotation velocity of the gas is not always
exactly equal to the circular velocity of a test particle on a circular orbit.
Contrasting with the data the cored mass model presented here is preferred
instead of a cuspy one.Comment: 8 pages, 8 figures. Accepted for publication in MNRA
Pseudospin excitations in coaxial nanotubes
In a 2DEG confined to two coaxial tubes the `tube degree of freedom' can be
described in terms of pseudospin-1/2 dynamics. The presence of tunneling
between the two tubes leads to a collective oscillation known as pseudospin
resonance. We employ perturbation theory to examine the dependence of the
frequency of this mode with respect to a coaxial magnetic field for the case of
small intertube distances. Coulomb interaction leads to a shift of the
resonance frequency and to a finite lifetime of the pseudospin excitations. The
presence of the coaxial magnetic field gives rise to pronounced peaks in the
shift of the resonance frequency. For large magnetic fields this shift vanishes
due to the effects of Zeeman splitting. Finally, an expression for the
linewidth of the resonance is derived. Numerical analysis of this expression
suggests that the linewidth strongly depends on the coaxial magnetic field,
which leads to several peaks of the linewidth as well as regions where damping
is almost completely suppressed.Comment: 11 pages, 7 figure
Solutions in Self-Dual Gravity Constructed Via Chiral Equations
The chiral model for self-dual gravity given by Husain in the context of the
chiral equations approach is discussed. A Lie algebra corresponding to a finite
dimensional subgroup of the group of symplectic diffeomorphisms is found, and
then use for expanding the Lie algebra valued connections associated with the
chiral model. The self-dual metric can be explicitly given in terms of harmonic
maps and in terms of a basis of this subalgebra.Comment: Plain Latex, 13 Pages, major revisions of style in the above proof,
several Comments added. Version to appear in Physical Review
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