105 research outputs found
D2-branes with magnetic flux in the presence of RR fields
D2-branes are studied in the context of Born-Infeld theory as a source of the
3-form RR gauge potential. Considering the static case with only a radial
magnetic field it is shown that a locally stable hemispherical deformation of
the brane exists which minimises the energy locally. Since the D2-brane carries
also the charge of D0-branes, and the RR spacetime potential is unbounded from
below, these can tunnel to condense on the D2-brane. The corresponding
instanton-like configuration and the tunneling rate are derived and discussed.Comment: 24 pages, 1 figure included, version to appear in NP
Supersphere
The spherical D2-brane solution is obtained without RR external background.
The solution is shown to preserve supersymmetries. The configurations
obtained depend on the integration constant . For the shape
of the solution is a deformed sphere. When, however, , the D2-brane
system seems to exhibit a brane-anti-brane configuration.Comment: 11 pages, 2 figure
General Criterion for the existence of Supertube and BIon in Curved Target Space
The supertube and BIon spike solutions are examined in a general curved
target space. The criteria for the existence of these solutions are explicitly
derived. Also the equation which the general BIon solution should satisfy is
derived.Comment: 12 pages, no figur
Fate of the Black String Instability
Gregory and Laflamme showed that certain nonextremal black strings (and
p-branes) are unstable to linearized perturbations. It is widely believed that
this instability will cause the black string horizon to classically pinch off
and then quantum mechanically separate, resulting in higher dimensional black
holes. We argue that this cannot happen. Under very mild assumptions, classical
event horizons cannot pinch off. Instead, they settle down to new static black
string solutions which are not translationally invariant along the string.Comment: 11 pages, v2: few clarifications and references adde
Fuzzy Sphere Dynamics and Non-Abelian DBI in Curved Backgrounds
We consider the non-Abelian action for the dynamics of -branes in the
background of -branes, which parameterises a fuzzy sphere using the SU(2)
algebra. We find that the curved background leads to collapsing solutions for
the fuzzy sphere except when we have branes in the background, which
is a realisation of the gravitational Myers effect. Furthermore we find the
equations of motion in the Abelian and non-Abelian theories are identical in
the large limit. By picking a specific ansatz we find that we can
incorporate angular momentum into the action, although this imposes restriction
upon the dimensionality of the background solutions. We also consider the case
of non-Abelian non-BPS branes, and examine the resultant dynamics using
world-volume symmetry transformations. We find that the fuzzy sphere always
collapses but the solutions are sensitive to the combination of the two
conserved charges and we can find expanding solutions with turning points. We
go on to consider the coincident 5-brane background, and again construct
the non-Abelian theory for both BPS and non-BPS branes. In the latter case we
must use symmetry arguments to find additional conserved charges on the
world-volumes to solve the equations of motion. We find that in the Non-BPS
case there is a turning solution for specific regions of the tachyon and radion
fields. Finally we investigate the more general dynamics of fuzzy
in the -brane background, and find collapsing solutions
in all cases.Comment: 49 pages, 3 figures, Latex; Version to appear in JHE
Anomalies and O-plane charges in orientifolded brane tilings
We investigate orientifold of brane tilings. We clarify how the cancellations
of gauge anomaly and Witten's anomaly are guaranteed by the conservation of the
D5-brane charge. We also discuss the relation between brane tilings and the
dual Calabi-Yau cones realized as the moduli spaces of gauge theories. Two
types of flavor D5-branes in brane tilings and corresponding superpotentials of
fundamental quark fields are proposed, and it is shown that the massless loci
of these quarks in the moduli space correctly reproduce the worldvolume of
flavor D7-branes in the Calabi-Yau cone dual to the fivebrane system.Comment: 46 pages, 19 figure
Aspects of higher curvature terms and U-duality
We discuss various aspects of dimensional reduction of gravity with the
Einstein-Hilbert action supplemented by a lowest order deformation formed as
the Riemann tensor raised to powers two, three or four. In the case of R^2 we
give an explicit expression, and discuss the possibility of extended coset
symmetries, especially SL(n+1,Z) for reduction on an n-torus to three
dimensions. Then we start an investigation of the dimensional reduction of R^3
and R^4 by calculating some terms relevant for the coset formulation, aiming in
particular towards E_8(8)/(Spin(16)/Z_2) in three dimensions and an
investigation of the derivative structure. We emphasise some issues concerning
the need for the introduction of non-scalar automorphic forms in order to
realise certain expected enhanced symmetries.Comment: 26 pp., 15 figs., plain te
The Exchange of Orientifold Two-Planes in M-theory
We propose an M-theory lift picture of the exchange among type IIA
orientifold two-planes. This consists in wrapping a M5-brane on a three-cycle
in the transverse space of the M-theory orientifold plane OM2. A flux
quantization condition for the three-form self-dual field strength, on the
worldvolume of the M5-brane is computed. This condition establishes the value
which explains the relative charge between two different OM2-planes. Also, we
find that the exchange of the four types of orientifold two-planes in string
theory, has a common picture in M-theory. Moreover, we find that the assignment
of the extra charge is fixed by cohomology and by the flux quantization of the
field strength G in M-theory. We conclude that cohomology is sufficient to
describe some orientifold properties in M-theory, that at string theory level,
only K-theory is able to explain.Comment: 23+1 pages, 6 figures. v2: typos corrected, references adde
Noncommutativity and Tachyon Condensation
We study the fuzzy or noncommutative Dp-branes in terms of infinitely many
unstable D0-branes, from which we can construct any Dp-branes. We show that the
tachyon condensation of the unstable D0-branes induces the noncommutativity. In
the infinite tachyon condensation limit, most of the unstable D0-branes
disappear and remaining D0-branes are actually the BPS D0-branes with the
correct noncommutative coordinates. For the fuzzy S^2 case, we explicitly show
only the D0-branes corresponding to the lowest Landau level survive in the
limit. We also show that a boundary state for a Dp-brane satisfying the
Dirichlet boundary condition on a curved submanifold embedded in the flat space
is not localized on the submanifold. This implies that the Dp-brane on it is
ambiguous at the string scale and solves the problem for a spherical D2-brane
with a unit flux on the world volume which should be equivalent to one
D0-brane. We also discuss the diffeomorphism in the D0-brane picture.Comment: 30 pages, references added, minor corrections and clarifications,
version to appear in JHE
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