12,250 research outputs found
Necessary conditions for having wormholes in f(R) gravity
For a generic which admits a polynomial expansion of at least third
order (i.e. ) we find the near-throat wormhole
solution. Necessary conditions for the existence of wormholes in such
theories are derived for both zero and non-zero matter sources. A particular
choice of energy-momentum reveals that the wormhole geometry satisfies the weak
energy condition (WEC). For a range of parameters even the strong energy
condition (SEC) is shown to be satisfied.Comment: 7 pages, 1 figur
Cloud of strings as source in -dimensional gravity
We present three parameters exact solutions with possible black holes in dimensional modified gravity coupled minimally
to a cloud of strings. These three parameters are the cloud of string
coupling constant and an integration constant . Although in general
one has to consider each set of parameters separately; for an even integer
greater than one we give a unified picture providing black holes. For
we analyze null / timelike geodesic within the context of particle confinement.Comment: 5 pages, no figures. Revised versio
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.
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