9,753 research outputs found
Interacting Intersections
Intersecting p-branes can be viewed as higher-dimensional interpretations of
multi-charge extremal p-branes, where some of the individual p-branes undergo
diagonal dimensional oxidation, while the others oxidise vertically. Although
the naive vertical oxidation of a single p-brane gives a continuum of p-branes,
a more natural description arises if one considers a periodic array of p-branes
in the higher dimension, implying a dependence on the compactification
coordinates. This still reduces to the single lower-dimensional p-brane when
viewed at distances large compared with the period. Applying the same logic to
the multi-charge solutions, we are led to consider more general classes of
intersecting p-brane solutions, again depending on the compactification
coordinates, which turn out to be described by interacting functions rather
than independent harmonic functions. These new solutions also provide a more
satisfactory interpretation for the lower-dimensional multi-charge p-branes,
which otherwise appear to be nothing more than the improbable coincidence of
charge-centres of individual constituents with zero binding energy.Comment: 20 pages, Latex, references adde
Almost Special Holonomy in Type IIA&M Theory
We consider spaces M_7 and M_8 of G_2 holonomy and Spin(7) holonomy in seven
and eight dimensions, with a U(1) isometry. For metrics where the length of the
associated circle is everywhere finite and non-zero, one can perform a
Kaluza-Klein reduction of supersymmetric M-theory solutions (Minkowksi)_4\times
M_7 or (Minkowksi)_3\times M_8, to give supersymmetric solutions
(Minkowksi)_4\times Y_6 or (Minkowksi)_3\times Y_7 in type IIA string theory
with a non-singular dilaton. We study the associated six-dimensional and
seven-dimensional spaces Y_6 and Y_7 perturbatively in the regime where the
string coupling is weak but still non-zero, for which the metrics remain
Ricci-flat but that they no longer have special holonomy, at the linearised
level. In fact they have ``almost special holonomy,'' which for the case of Y_6
means almost Kahler, together with a further condition. For Y_7 we are led to
introduce the notion of an ``almost G_2 manifold,'' for which the associative
3-form is closed but not co-closed. We obtain explicit classes of non-singular
metrics of almost special holonomy, associated with the near Gromov-Hausdorff
limits of families of complete non-singular G_2 and Spin(7) metrics.Comment: Latex, 26 page
Electrodynamics of Black Holes in STU Supergravity
External magnetic fields can probe the composite structure of black holes in
string theory. With this motivation we study magnetised four-charge black holes
in the STU model, a consistent truncation of maximally supersymmetric
supergravity with four types of electromagnetic fields. We employ solution
generating techniques to obtain Melvin backgrounds, and black holes in these
backgrounds. For an initially electrically charged static black hole immersed
in magnetic fields, we calculate the resultant angular momenta and analyse
their global structure. Examples are given for which the ergoregion does not
extend to infinity. We calculate magnetic moments and gyromagnetic ratios via
Larmor's formula. Our results are consistent with earlier special cases. A
scaling limit and associated subtracted geometry in a single surviving magnetic
field is shown to lift to . Magnetizing magnetically charged
black holes give static solutions with conical singularities representing
strings or struts holding the black holes against magnetic forces. In some
cases it is possible to balance these magnetic forces.Comment: 31 page
Brane Worlds in Collision
We obtain an exact solution of the supergravity equations of motion in which
the four-dimensional observed universe is one of a number of colliding
D3-branes in a Calabi-Yau background. The collision results in the
ten-dimensional spacetime splitting into disconnected regions, bounded by
curvature singularities. However, near the D3-branes the metric remains static
during and after the collision. We also obtain a general class of solutions
representing -brane collisions in arbitrary dimensions, including one in
which the universe ends with the mutual annihilation of a positive-tension and
negative-tension 3-brane.Comment: RevTex, 4 pages, 1 figure, typos and minor errors correcte
On the mass of a Kerr-anti-de Sitter spacetime in D dimensions
We show how to compute the mass of a Kerr-anti-de Sitter spacetime with
respect to the anti-de Sitter background in any dimension, using a
superpotential which has been derived from standard Noether identities. The
calculation takes no account of the source of the curvature and confirms
results obtained for black holes via the first law of thermodynamics.Comment: minor changes; accepted by CQ
Variant N=(1,1) Supergravity and (Minkowski)_4 x S^2 Vacua
We construct the fermionic sector and supersymmetry transformation rules of a
variant N=(1,1) supergravity theory obtained by generalized Kaluza-Klein
reduction from seven dimensions. We show that this model admits both
(Minkowski)_4 x S^2 and (Minkowski)_3 x S^3 vacua. We perform a consistent
Kaluza-Klein reduction on S^2 and obtain D=4, N=2 supergravity coupled to a
vector multiplet, which can be consistently truncated to give rise to D=4, N=1
supergravity with a chiral multiplet.Comment: Latex, 17 pages. Version appearing in Classical and Quantum Gravit
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