273 research outputs found
Symplectic and Killing Symmetries of AdS Gravity: Holographic vs Boundary Gravitons
The set of solutions to the AdS Einstein gravity with Brown-Henneaux
boundary conditions is known to be a family of metrics labeled by two arbitrary
periodic functions, respectively left and right-moving. It turns out that there
exists an appropriate presymplectic form which vanishes on-shell. This promotes
this set of metrics to a phase space in which the Brown-Henneaux asymptotic
symmetries become symplectic symmetries in the bulk of spacetime. Moreover, any
element in the phase space admits two global Killing vectors. We show that the
conserved charges associated with these Killing vectors commute with the
Virasoro symplectic symmetry algebra, extending the Virasoro symmetry algebra
with two generators. We discuss that any element in the phase space
falls into the coadjoint orbits of the Virasoro algebras and that each orbit is
labeled by the Killing charges. Upon setting the right-moving function
to zero and restricting the choice of orbits, one can take a near-horizon
decoupling limit which preserves a chiral half of the symplectic symmetries.
Here we show two distinct but equivalent ways in which the chiral Virasoro
symplectic symmetries in the near-horizon geometry can be obtained as a limit
of the bulk symplectic symmetries.Comment: 39 pages, v2: a reference added, the version to appear in JHE
Solitons in Five Dimensional Minimal Supergravity: Local Charge, Exotic Ergoregions, and Violations of the BPS Bound
We describe a number of striking features of a class of smooth solitons in
gauged and ungauged minimal supergravity in five dimensions. The solitons are
globally asymptotically flat or asymptotically AdS without any Kaluza-Klein
directions but contain a minimal sphere formed when a cycle pinches off in the
interior of the spacetime. The solutions carry a local magnetic charge and many
have rather unusual ergosurfaces. Perhaps most strikingly, many of the solitons
have more electric charge or, in the asymptotically AdS case, more electric
charge and angular momentum than is allowed by the usual BPS bound. We comment
on, but do not resolve, the new puzzle this raises for AdS/CFT.Comment: 60 pages, 12 figures, 3 table
<i>Cocconeis molesta</i> KĂĽtz., <i>C. diaphana</i> W.Sm. and <i>C. dirupta</i> W.Greg. (Bacillariophyta): type material, ambiguities and possible synonymies
F.T. Kützing introduced Cocconeis molesta with only an uninformative description and a poor illustration: C. molesta has small, oblong valves and is an epiphyte. Another species, Cocconeis diaphana, described by William Smith, is said to have larger valves than C. molesta, with frustules that are relatively oblong. Smith described two forms: one with a distinct fascia on its raphe valve (var. β), the other without this feature. A third species, Cocconeis dirupta was described by Gregory, who expressed doubts that it differed from C. diaphana. Finally, Cocconeis molesta var. crucifera Grunow was first introduced in Van Heurck’s Atlas but was subsequently treated by Van Heurck as a synonym of C. molesta. No previous account has examined the type material of these species. In this paper, we undertake that task and examine type slides and raw material in order to discriminate these different taxa. We conclude by recognizing three species: Cocconeis molesta Kütz., C. diaphana W.Sm. and C. dirupta W.Greg. Cocconeis diaphana var. β is considered to be a synonym of C. dirupta and C. molesta var. crucifera is considered to be a synonym of C. molesta. Lectotypes are designated for C. diaphana and C. dirupta
Classical central extension for asymptotic symmetries at null infinity in three spacetime dimensions
The symmetry algebra of asymptotically flat spacetimes at null infinity in
three dimensions is the semi-direct sum of the infinitesimal diffeomorphisms on
the circle with an abelian ideal of supertranslations. The associated charge
algebra is shown to admit a non trivial classical central extension of Virasoro
type closely related to that of the anti-de Sitter case.Comment: 4 sign mistakes due to a change of conventions are corrected in
section 2, none of the conclusions are affected, takes precedence over
published version, including corrigendu
Relaxing the Parity Conditions of Asymptotically Flat Gravity
Four-dimensional asymptotically flat spacetimes at spatial infinity are
defined from first principles without imposing parity conditions or
restrictions on the Weyl tensor. The Einstein-Hilbert action is shown to be a
correct variational principle when it is supplemented by an anomalous
counter-term which breaks asymptotic translation, supertranslation and
logarithmic translation invariance. Poincar\'e transformations as well as
supertranslations and logarithmic translations are associated with finite and
conserved charges which represent the asymptotic symmetry group. Lorentz
charges as well as logarithmic translations transform anomalously under a
change of regulator. Lorentz charges are generally non-linear functionals of
the asymptotic fields but reduce to well-known linear expressions when parity
conditions hold. We also define a covariant phase space of asymptotically flat
spacetimes with parity conditions but without restrictions on the Weyl tensor.
In this phase space, the anomaly plays classically no dynamical role.
Supertranslations are pure gauge and the asymptotic symmetry group is the
expected Poincar\'e group.Comment: Four equations corrected. Two references adde
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