687 research outputs found
Taub-NUT/Bolt Black Holes in Gauss-Bonnet-Maxwell Gravity
We present a class of higher dimensional solutions to Gauss-Bonnet-Maxwell
equations in dimensions with a U(1) fibration over a -dimensional
base space . These solutions depend on two extra parameters, other
than the mass and the NUT charge, which are the electric charge and the
electric potential at infinity . We find that the form of metric is
sensitive to geometry of the base space, while the form of electromagnetic
field is independent of . We investigate the existence of
Taub-NUT/bolt solutions and find that in addition to the two conditions of
uncharged NUT solutions, there exist two other conditions. These two extra
conditions come from the regularity of vector potential at and the fact
that the horizon at should be the outer horizon of the black hole. We
find that for all non-extremal NUT solutions of Einstein gravity having no
curvature singularity at , there exist NUT solutions in
Gauss-Bonnet-Maxwell gravity. Indeed, we have non-extreme NUT solutions in
dimensions only when the -dimensional base space is chosen to be
. We also find that the Gauss-Bonnet-Maxwell gravity has
extremal NUT solutions whenever the base space is a product of 2-torii with at
most a 2-dimensional factor space of positive curvature, even though there a
curvature singularity exists at . We also find that one can have bolt
solutions in Gauss-Bonnet-Maxwell gravity with any base space. The only case
for which one does not have black hole solutions is in the absence of a
cosmological term with zero curvature base space.Comment: 23 pages, 3 figures, typos fixed, a few references adde
Thermodynamics of Asymptotically Flat Charged Black Holes in Third Order Lovelock Gravity
We present a new class of asymptotically flat charge static solutions in
third order Lovelock gravity. These solutions present black hole solutions with
two inner and outer event horizons, extreme black holes or naked singularities
provided the parameters of the solutions are chosen suitable. We find that the
uncharged asymptotically flat solutions can present black hole with two inner
and outer horizons. This kind of solution does not exist in Einstein or
Gauss-Bonnet gravity, and it is a special effect in third order Lovelock
gravity. We compute temperature, entropy, charge, electric potential and mass
of the black hole solutions, and find that these quantities satisfy the first
law of thermodynamics. We also perform a stability analysis by computing the
determinant of Hessian matrix of the mass with respect to its thermodynamic
variables in both the canonical and the grand-canonical ensembles, and show
that there exists only an intermediate stable phase.Comment: 16 pages, two figures, a few references, and one sections added. Some
properties of these new solutions which are different from Gauss-Bonnet
gravity have been highlighte
NUT-Charged Black Holes in Gauss-Bonnet Gravity
We investigate the existence of Taub-NUT/bolt solutions in Gauss-Bonnet
gravity and obtain the general form of these solutions in dimensions. We
find that for all non-extremal NUT solutions of Einstein gravity having no
curvature singularity at , there exist NUT solutions in Gauss-Bonnet
gravity that contain these solutions in the limit that the Gauss-Bonnet
parameter goes to zero. Furthermore there are no NUT solutions in
Gauss-Bonnet gravity that yield non-extremal NUT solutions to Einstein gravity
having a curvature singularity at in the limit . Indeed,
we have non-extreme NUT solutions in dimensions with non-trivial
fibration only when the -dimensional base space is chosen to be
. We also find that the Gauss-Bonnet gravity has extremal NUT
solutions whenever the base space is a product of 2-torii with at most a
2-dimensional factor space of positive curvature. Indeed, when the base space
has at most one positively curved two dimensional space as one of its factor
spaces, then Gauss-Bonnet gravity admits extreme NUT solutions, even though
there a curvature singularity exists at . We also find that one can have
bolt solutions in Gauss-Bonnet gravity with any base space with factor spaces
of zero or positive constant curvature. The only case for which one does not
have bolt solutions is in the absence of a cosmological term with zero
curvature base space.Comment: 20 pages, referrence added, a few typos correcte
Topological Black Holes in Lovelock-Born-Infeld Gravity
In this paper, we present topological black holes of third order Lovelock
gravity in the presence of cosmological constant and nonlinear electromagnetic
Born-Infeld field. Depending on the metric parameters, these solutions may be
interpreted as black hole solutions with inner and outer event horizons, an
extreme black hole or naked singularity. We investigate the thermodynamics of
asymptotically flat solutions and show that the thermodynamic and conserved
quantities of these black holes satisfy the first law of thermodynamic. We also
endow the Ricci flat solutions with a global rotation and calculate the finite
action and conserved quantities of these class of solutions by using the
counterterm method. We compute the entropy through the use of the Gibbs-Duhem
relation and find that the entropy obeys the area law. We obtain a Smarr-type
formula for the mass as a function of the entropy, the angular momenta, and the
charge, and compute temperature, angular velocities, and electric potential and
show that these thermodynamic quantities coincide with their values which are
computed through the use of geometry. Finally, we perform a stability analysis
for this class of solutions in both the canonical and the grand-canonical
ensemble and show that the presence of a nonlinear electromagnetic field and
higher curvature terms has no effect on the stability of the black branes, and
they are stable in the whole phase space.Comment: 14 page
D7-Brane Moduli vs. F-Theory Cycles in Elliptically Fibred Threefolds
We study the space of geometric and open string moduli of type IIB
compactifications from the perspective of complex structure deformations of
F-theory. In order to find a correspondence, we work in the weak coupling limit
and for simplicity focus on compactifications to 6 dimensions. Starting from
the topology of D7-branes and O7-planes, we construct the 3-cycles of the
F-theory threefold. We achieve complete agreement between the degrees of
freedom of the Weierstrass model and the complex structure deformations of the
elliptic Calabi-Yau. All relevant quantities are expressed in terms of the
topology of the base space, allowing us to formulate our results for general
base spaces.Comment: 40 pages, 15 figures, references adde
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