1,081 research outputs found
Black Holes and Naked Singularities in Low Energy Limit of String Gravity with Modulus Field
We show that the black hole solutions of the effective string theory action,
where one-loop effects that couple the moduli to gravity via a Gauss-Bonnet
term are taken into account, admit primary scalar hair. The requirement of
absence of naked singularities imposes an upper bound on the scalar charges.Comment: more details are added and some misprint are correcte
Black Holes of a Minimal Size in String Gravity
A lower limit for a neutral black hole size is obtained in the frames of the
string gravity model with the second order curvature correction. It is shown
that this effect remains when the third order curvature correction is also
taken into account and argued that such restriction does exist in all
perturbative orders of curvature expansions.Comment: 6 LaTeX pages, 1 PostScript figure (epsfig.sty), minor changes in the
text and references, submitted to Int.J.Mod.Phy
Internal structure of a Maxwell-Gauss-Bonnet black hole
The influence of the Maxwell field on a static, asymptotically flat and
spherically-symmetric Gauss-Bonnet black hole is considered. Numerical
computations suggest that if the charge increases beyond a critical value, the
inner determinant singularity is replaced by an inner singular horizon.Comment: 5 pages, 5 figures, published version with minor change
Wormholes and Naked Singularities in Brans-Dicke cosmology
We perform analytical and numerical study of static spherically symmetric
solutions in the context of Brans-Dicke-like cosmological model by Elizalde et
al. with an exponential potential. In this model the phantom regime arises
without the appearance of any ghost degree of freedom due to the specific form
of coupling. For the certain parameter ranges the model contains a regular
solution which we interpret as a wormhole in an otherwise dS Universe. We put
several bounds on the parameter values: . The numerical
solution could mimic the Schwarzschild one, so the original model is consistent
with astrophysical and cosmological observational data. However differences
between our solution and the Schwarzschild one can be quite large, so black
hole candidate observations could probably place further limits on the
value.Comment: 20 pages, 6 figures, typos & errors correcte
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