568 research outputs found
Existence of Majorana fermions for M-branes wrapped in space and time
We show that it is possible to define Majorana (s)pinor fields on M-branes
which have been identified under the action of the antipodal map on the adS
factor of the throat geometry, or which have been wrapped on two-cycles of
arbitrary genus. This is an important consistency check, since it means that
one may still take the generators of supertranslations in superspace to
transform as Majorana fermions under the adjoint action of , even
though the antipodally identified M2-brane is {\it not} space-orientable. We
point out that similar conclusions hold for any p-branes which have the generic
(adS)(Sphere) throat geometry.Comment: 10 pages REVTe
Hawking and Page on the brane
We show that the Hawking-Page phase transition of a CFT on AdS_{d-1} weakly
coupled to gravity has a dual bulk description in terms of a phase transition
between a black string and a thermal gas on AdS_{d}. At even lower temperatures
the black string develops a Gregory Laflamme instability, which is dual to
black hole evaporation in the boundary theory.Comment: 8 pages, 1 figure; v2: typos in some formulas corrected; v3:
discussion improve
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
Obstructions to Pin Structures on Kleinian Manifolds
We develop various topological notions on four-manifolds of Kleinian
signature . In particular, we extend the concept of `Kleinian metric
homotopy' to non-orientable manifolds. We then derive the topological
obstructions to pin-Klein cobordism, for all of the pin groups. Finally, we
discuss various examples and applications which arise from this work.Comment: 20 pages, Latex, 2 xfigures available from Andrew Chamblin at
[email protected]
Comment on ``Absence of abelian Higgs hair for extremal black holes''
We examine the claim of Chamblin et. al. that extreme black holes cannot
support abelian Higgs hair. We provide evidence that contradicts this claim and
discuss reasons for this discrepancy.Comment: 1 page 2 figures, revised titl
Can black holes and naked singularities be detected in accelerators?
We study the conditions for the existence of black holes that can be produced
in colliders at TeV-scale if the space-time is higher dimensional. On employing
the microcanonical picture, we find that their life-times strongly depend on
the details of the model. If the extra dimensions are compact (ADD model),
microcanonical deviations from thermality are in general significant near the
fundamental TeV mass and tiny black holes decay more slowly than predicted by
the canonical expression, but still fast enough to disappear almost
instantaneously. However, with one warped extra dimension (RS model),
microcanonical corrections are much larger and tiny black holes appear to be
(meta)stable. Further, if the total charge is not zero, we argue that naked
singularities do not occur provided the electromagnetic field is strictly
confined on an infinitely thin brane. However, they might be produced in
colliders if the effective thickness of the brane is of the order of the
fundamental length scale (~1/TeV).Comment: 6 pages, RevTeX 3, 1 figure and 1 table, important changes and
addition
Non-BPS D8-branes and Dynamic Domain Walls in Massive IIA Supergravities
We study the D8-branes of the Romans massive IIA supergravity theory using
the coupled supergravity and worldvolume actions. D8 branes can be regarded as
domain walls with the jump in the extrinsic curvature at the brane given by the
Israel matching conditions. We examine the restrictions that these conditions
place on extreme and non-extreme solutions and find that they rule out some of
the supersymmetric solutions given by Bergshoeff {\em et al}. We consider what
happens when the dilaton varies on the worldvolume of the brane, which implies
that the brane is no longer static. We obtain a family of D8-brane solutions
parametrized by a non-extremality term on each side of the brane and the
asymptotic values of the 10-form field. The non-extremality parameters can be
related to the velocity of the brane. We also study 8-brane solutions of a
massive IIA supergravity theory introduced by Howe, Lambert and West. This
theory also admits a 10-form formulation, but the 10-form is not a R-R sector
field and so these 8-branes are not D-branes.Comment: 23 pages REVTeX, 2 .eps figures. This paper completely replaces and
extends an earlier paper (hep-th/9712112) by Chamblin and Perr
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