16,733 research outputs found
Boundary Conditions for Kerr-AdS Perturbations
The Teukolsky master equation and its associated spin-weighted spheroidal
harmonic decomposition simplify considerably the study of linear gravitational
perturbations of the Kerr(-AdS) black hole. However, the formulation of the
problem is not complete before we assign the physically relevant boundary
conditions. We find a set of two Robin boundary conditions (BCs) that must be
imposed on the Teukolsky master variables to get perturbations that are
asymptotically global AdS, i.e. that asymptotes to the Einstein Static
Universe. In the context of the AdS/CFT correspondence, these BCs allow a
non-zero expectation value for the CFT stress-energy tensor while keeping fixed
the boundary metric. When the rotation vanishes, we also find the gauge
invariant differential map between the Teukolsky and the Kodama-Ishisbashi
(Regge-Wheeler-Zerilli) formalisms. One of our Robin BCs maps to the scalar
sector and the other to the vector sector of the Kodama-Ishisbashi
decomposition. The Robin BCs on the Teukolsky variables will allow for a
quantitative study of instability timescales and quasinormal mode spectrum of
the Kerr-AdS black hole. As a warm-up for this programme, we use the Teukolsky
formalism to recover the quasinormal mode spectrum of global AdS-Schwarzschild,
complementing previous analysis in the literature.Comment: 33 pages, 6 figure
AdS nonlinear instability: moving beyond spherical symmetry
Anti-de Sitter (AdS) is conjectured to be nonlinear unstable to a weakly
turbulent mechanism that develops a cascade towards high frequencies, leading
to black hole formation [1,2]. We give evidence that the gravitational sector
of perturbations behaves differently from the scalar one studied in [2]. In
contrast with [2], we find that not all gravitational normal modes of AdS can
be nonlinearly extended into periodic horizonless smooth solutions of the
Einstein equation. In particular, we show that even seeds with a single normal
mode can develop secular resonances, unlike the spherically symmetric scalar
field collapse studied in [2]. Moreover, if the seed has two normal modes, more
than one resonance can be generated at third order, unlike the spherical
collapse of [2]. We also show that weak turbulent perturbative theory predicts
the existence of direct and inverse cascades, with the former dominating the
latter for equal energy two-mode seeds.Comment: 7 pages, no figures, 2 table
Bridge over troubled gas: clusters and associations under the SMC and LMC tidal stresses
We obtained SOAR telescope B and V photometry of 14 star clusters and 2
associations in the Bridge tidal structure connecting the LMC and SMC. These
objects are used to study the formation and evolution of star clusters and
associations under tidal stresses from the Clouds. Typical star clusters in the
Bridge are not richly populated and have in general relatively large diameters
(~30-35 pc), being larger than Galactic counterparts of similar age. Ages and
other fundamental parameters are determined with field-star decontaminated
photometry. A self-consistent approach is used to derive parameters for the
most-populated sample cluster NGC 796 and two young CMD templates built with
the remaining Bridge clusters. We find that the clusters are not coeval in the
Bridge. They range from approximately a few Myr (still related to optical HII
regions and WISE and Spitzer dust emission measurements) to about 100-200 Myr.
The derived distance moduli for the Bridge objects suggests that the Bridge is
a structure connecting the LMC far-side in the East to the foreground of the
SMC to the West. Most of the present clusters are part of the tidal dwarf
candidate D 1, which is associated with an H I overdensity. We find further
evidence that the studied part of the Bridge is evolving into a tidal dwarf
galaxy, decoupling from the Bridge.Comment: 15 pages, 15 figures, MNRAS, Accepted 2015 July 2
Localised Black Holes
We numerically construct asymptotically global black holes that are localised on the . These are
solutions to type IIB supergravity with horizon topology that
dominate the theory in the microcanonical ensemble at small energies. At higher
energies, there is a first-order phase transition to
-Schwarzschild. By the AdS/CFT
correspondence, this transition is dual to spontaneously breaking the
R-symmetry of super Yang-Mills down to . We extrapolate
the location of this phase transition and compute the expectation value of the
resulting scalar operators in the low energy phase.Comment: 11 pages, 6 figure
Lumpy AdS S Black Holes and Black Belts
Sufficiently small Schwarzschild black holes in global AdSS are
Gregory-Laflamme unstable. We construct new families of black hole solutions
that bifurcate from the onset of this instability and break the full SO
symmetry group of the S down to SO. These new "lumpy" solutions are
labelled by the harmonics . We find evidence that the branch
never dominates the microcanonical/canonical ensembles and connects through a
topology-changing merger to a localised black hole solution with S
topology. We argue that these S black holes should become the dominant
phase in the microcanonical ensemble for small enough energies, and that the
transition to Schwarzschild black holes is first order. Furthermore, we find
two branches of solutions with . We expect one of these branches to
connect to a solution containing two localised black holes, while the other
branch connects to a black hole solution with horizon topology which we call a "black belt".Comment: 20 pages (plus 17 pages for Appendix on Kaluza-Klein Holography), 14
figure
Scaling limit for a drainage network model
We consider the two dimensional version of a drainage network model
introduced by Gangopadhyay, Roy and Sarkar, and show that the appropriately
rescaled family of its paths converges in distribution to the Brownian web. We
do so by verifying the convergence criteria proposed by Fontes, Isopi, Newman
and Ravishankar.Comment: 15 page
Quasinormal modes of asymptotically flat rotating black holes
We study the main properties of general linear perturbations of rotating
black holes in asymptotically flat higher-dimensional spacetimes. In
particular, we determine the quasinormal mode (QNM) spectrum of singly spinning
and equal angular momenta Myers-Perry black holes (MP BHs). Emphasis is also
given to the timescale of the ultraspinning and bar-mode instabilities in these
two families of MP BHs. For the bar-mode instabilities in the singly spinning
MP BH, we find excellent agreement with our linear analysis and the non-linear
time evolution of Shibata and Yoshino for d=6,7 spacetime dimensions. We find
that d=5 singly spinning BHs are linearly stable. In the context of studying
general relativity in the large dimension limit, we obtain the QNM spectrum of
Schwarzschild BHs and rotating MP BHs for large dimensions. We identify two
classes of modes. For large dimensions, we find that in the limit of zero
rotation, unstable modes of the MP BHs connect to a class of Schwarzschild QNMs
that saturate to finite values.Comment: 52 pages. 25 figure
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