177 research outputs found
Black holes and the classical model of a particle in Einstein non-linear electrodynamics theory
Modified by a logarithmic term, the non-linear electrodynamics (NED) model of
the Born-Infeld (BI) action is reconsidered. Unlike the standard BI action,
this choice provides interesting integrals of the Einstein-NED equations. It is
found that the spherical matching process for a regular black hole entails
indispensable surface stresses that vanish only for a specific value of the BI
parameter. This solution represents a classical model of an elementary particle
whose radius coincides with the horizon. In flat space time, a charged particle
becomes a conducting shell with a radius proportional to the BI parameter.Comment: 11 pages, no figure, To appear in Phys. Lett.
2+1-dimensional traversable wormholes supported by positive energy
We revisit the shapes of the throats of wormholes, including thin-shell
wormholes (TSWs) in dimensions. In particular, in the case of TSWs this
is done in a flat dimensional bulk spacetime by using the standard method
of cut-and-paste. Upon departing from a pure time-dependent circular shape
i.e., for the throat, we employ a dependent
closed loop of the form and in terms of we find the surface energy density on the throat.
For the specific convex shapes we find that the total energy which supports the
wormhole is positive and finite. In addition to that we analyze the general
wormhole's throat. By considering a specific equation of instead of and upon certain choices of functions
for we find the total energy of the wormhole to be
positive.Comment: 8 pages, 9 figures, final version to appear in EPJ
Screening of the Reissner-Nordstr\"om charge by a thin-shell of dust matter
A concentric charged thin-shell encircling a Reissner-Nordstr\"{o}m black
hole screens the clectric / magnetic charge completely to match with an
external Schwarzschild black hole. The negative mass thin-shell is shown to be
stable against radial perturbations. It is shown further that by reversing the
roles of inside Reissner-Nordstr\"{o}m and outside Schwarzschild geometries the
mass of the appropriate shell becomes positive.Comment: 5 pages, one figure, final version published in EPJ
Absence of Buckling in Nerve Fiber
In this study we give a geometrical model which employs the smoothness of
nerve fibers as differentiable curves. We show that a nerve fiber may encounter
large curvature due to the possible helicial bending and hence it could cause
the fiber to buckle. However, its membrane structure provides a mechanism,
entirely geometrical to avoid it. To overcome the challenge of emerging helix
we project it into a plane.Comment: 7 pages no figure. Final version presented at The 10th International
Physics Conference of the Balkan Physical Union (BPU10), 26-30 August 2018.
To be published in AIP Conference Proceeding
A topological metric in 2+1-dimensions
Real-valued triplet of scalar fields as source gives rise to a metric which
tilts the scalar, not the light cone, in 2+1-dimensions. The topological metric
is static, regular and it is characterized by an integer . The problem is formulated as a harmonic map of Riemannian manifolds in
which the integer equals to the degree of the map.Comment: 4 pages no figure, final version accepted for publication in EPJ
Black holes from multiplets of scalar fields in 2+1- and 3+1-dimensions
We obtain classes of black hole solutions constructed from multiplets of
scalar fields in 2+1 / 3+1 dimensions. The multi-component scalars don't
undergo a symmetry breaking so that only the isotropic modulus is effective.
The Lagrangian is supplemented by a self-interacting potential which plays
significant role in obtaining the exact solutions. In 2+1 / 3+1 dimensions
doublet / triplet of scalars is effective which enriches the available black
hole spacetimes and creates useful Liouville weighted field theoretic models.Comment: 10 pages, 10 figures, final version accepted for publication in EPJ
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