1,338 research outputs found
On the Eleven-Dimensional Origins of Polarized D0-branes
The worldvolume theory of a D0-brane contains a multiplet of fermions which
can couple to background spacetime fields. This coupling implies that a
D0-brane may possess multipole moments with respect to the various type IIA
supergravity fields. Different such polarization states of the D0-brane will
thus generate different long-range supergravity fields, and the corresponding
semi-classical supergravity solutions will have different geometries. In this
paper, we reconsider such solutions from an eleven-dimensional perspective. We
thus begin by deriving the ``superpartners'' of the eleven-dimensional
graviton. These superpartners are obtained by acting on the purely bosonic
solution with broken supersymmetries and, in theory, one can obtain the full
BPS supermultiplet of states. When we dimensionally reduce a polarized
supergraviton along its direction of motion, we recover a metric which
describes a polarized D0-brane. On the other hand, if we compactify along the
retarded null direction we obtain the short distance, or ``near-horizon'',
geometry of a polarized D0-brane, which is related to finite Matrix theory.
The various dipole moments in this case can only be defined once the
eleven-dimensional metric is ``regularized'' and, even then, they are formally
infinite. We argue, however, that this is to be expected in such a
non-asymptotically flat spacetime. Moreover, we find that the superpartners of
the D0-brane, in this r \ra 0 limit, possess neither spin nor D2-brane dipole
moments.Comment: 20 pages, LaTeX. More references added, and a correction made to the
supercharge. Version to be published in JHE
BPS States of the Non-Abelian Born-Infeld Action
We argue that the trace structure of the non-abelian Born-Infeld action can
be fixed by demanding that the action be linearised by certain
energy-minimising BPS-like configurations. It is shown how instantons in
D4-branes, SU(2) monopoles and dyons in D3-branes, and vortices in D2-branes
are all BPS states of the action recently proposed by Tseytlin. The T-dual
worldvolume theories of D-strings and D0-branes are also considered. All such
configurations can be dealt with exactly within the context of non-abelian
Born-Infeld theory since, given the relevant BPS-like condition, the action
reduces to that of Yang-Mills theory. The worldvolume energy of such
configurations is an absolute minimum. It would seem, moreover, that such an
analysis holds for the symmetrised trace structure of Tseytlin's proposal only.Comment: 11 pages, LaTeX. Much condensed version to appear in Phys. Lett.
On the covariance of the Dirac-Born-Infeld-Myers action
A covariant version of the non-abelian Dirac-Born-Infeld-Myers action is
presented. The non-abelian degrees of freedom are incorporated by adjoining to
the (bosonic) worldvolume of the brane a number of anticommuting fermionic
directions corresponding to boundary fermions in the string picture. The
proposed action treats these variables as classical but can be given a matrix
interpretation if a suitable quantisation prescription is adopted. After
gauge-fixing and quantisation of the fermions, the action is shown to be in
agreement with the Myers action derived from T-duality. It is also shown that
the requirement of covariance in the above sense leads to a modified WZ term
which also agrees with the one proposed by Myers.Comment: 18 pages. Minor alterations to the text; references adde
Ricci-Flat Branes
Up to overall harmonic factors, the D8-brane solution of the massive type IIA
supergravity theory is the product of nine-dimensional Minkowski space (the
worldvolume) with the real line (the transverse space). We show that the
equations of motion allow for the worldvolume metric to be generalised to an
arbitrary Ricci-flat one. If this nine-dimensional Ricci-flat manifold admits
Killing spinors, then the resulting solutions are supersymmetric and satisfy
the usual Bogomol'nyi bound, although they preserve fewer than the usual one
half of the supersymmetries. We describe the possible choices of such
manifolds, elaborating on the connection between the existence of Killing
spinors and the self-duality condition on the curvature two-form. Since the
D8-brane is a domain wall in ten dimensions, we are led to consider the general
case: domain walls in any supergravity theory. Similar considerations hold here
also. Moreover, it is shown that the worldvolume of any magnetic brane --- of
which the domain walls are a specific example --- can be generalised in
precisely the same way. The general class of supersymmetric solutions have
gravitational instantons as their spatial sections. Some mention is made of the
worldvolume solitons of such branes.Comment: 26 pages, LaTe
Decay Modes of Intersecting Fluxbranes
Just as the single fluxbrane is quantum mechanically unstable to the
nucleation of a locally charged spherical brane, so intersecting fluxbranes are
unstable to various decay modes. Each individual element of the intersection
can decay via the nucleation of a spherical brane, but uncharged spheres can
also be nucleated in the region of intersection. For special values of the
fluxes, however, intersecting fluxbranes are supersymmetric, and so are
expected to be stable. We explicitly consider the instanton describing the
decay modes of the two--element intersection (an F5-brane in the string theory
context), and show that in dimensions greater than four the action for the
decay mode of the supersymmetric intersection diverges. This observation allows
us to show that stable intersecting fluxbranes should also exist in type 0A
string theory.Comment: 19 pages, 6 figures. References adde
Boundary States for Supertubes in Flat Spacetime and Godel Universe
We construct boundary states for supertubes in the flat spacetime. The T-dual
objects of supertubes are moving spiral D1-branes (D-helices). Since we can
obtain these D-helices from the usual D1-branes via null deformation, we can
construct the boundary states for these moving D-helices in the covariant
formalism. Using these boundary states, we calculate the vacuum amplitude
between two supertubes in the closed string channel and read the open string
spectrum via the open closed duality. We find there are critical values of the
energy for on-shell open strings on the supertubes due to the non-trivial
stringy correction. We also consider supertubes in the type IIA Godel universe
in order to use them as probes of closed timelike curves. This universe is the
T-dual of the maximally supersymmetric type IIB PP-wave background. Since the
null deformations of D-branes are also allowed in this PP-wave, we can
construct the boundary states for supertubes in the type IIA Godel universe in
the same way. We obtain the open string spectrum on the supertube from the
vacuum amplitude between supertubes. As a consequence, we find that the
tachyonic instability of open strings on the supertube, which is the signal of
closed time like curves, disappears due to the stringy correction.Comment: 26 pages, 3 figures, v2: explanations added, references added, v3:
explanations adde
Closed Geodesics on Godel-type Backgrounds
We consider radial oscillations of supertube probes in the Godel-type
background which is U-dual to the compactified pp-wave obtained from the
Penrose limit of the NS five-brane near horizon geometry. The supertube probe
computation can be carried over directly to a string probe calculation on the
U-dual background. The classical equations of motion are solved explicitly. In
general, the probe is not restricted to travel unidirectionally through any
global time coordinate. In particular, we find geodesics that close.Comment: latex, 15 pages, 1 figure. v3: reference added, clarifications added
and some discussions expande
Supertube domain-walls and elimination of closed time-like curves in string theory
We show that some novel physics of supertubes removes closed time-like curves
from many supersymmetric spaces which naively suffer from this problem. The
main claim is that supertubes naturally form domain-walls, so while analytical
continuation of the metric would lead to closed time-like curves, across the
domain-wall the metric is non-differentiable, and the closed time-like curves
are eliminated. In the examples we study the metric inside the domain-wall is
always of the G\"odel type, while outside the shell it looks like a localized
rotating object, often a rotating black hole. Thus this mechanism prevents the
appearance of closed time-like curves behind the horizons of certain rotating
black holes.Comment: 22 pages, JHEP3 class. V2: Some corrections and clariffications,
references added. V3: more corrections to formulas, results unchanged. V4:
minor typos, as published in PR
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