147 research outputs found

### Classical instability of Kerr-AdS black holes and the issue of final state

It is now established that small Kerr-Anti-de Sitter (Kerr-AdS) black holes
are unstable against scalar perturbations, via superradiant amplification
mechanism. We show that small Kerr-AdS black holes are also unstable against
gravitational perturbations and we compute the features of this instability. We
also describe with great detail the evolution of this instability. In
particular, we identify its endpoint state. It corresponds to a Kerr-AdS black
hole whose boundary is an Einstein universe rotating with the light velocity.
This black hole is expected to be slightly oblate and to co-exist in
equilibrium with a certain amount of outside radiation.Comment: 11 pages, RevTex4. v2: small typos corrected. Version to appear in
Phys. Rev.

### Quasinormal modes of black holes in anti-de Sitter space: a numerical study of the eikonal limit

Using series solutions and time-domain evolutions, we probe the eikonal limit
of the gravitational and scalar-field quasinormal modes of large black holes
and black branes in anti-de Sitter backgrounds. These results are particularly
relevant for the AdS/CFT correspondence, since the eikonal regime is
characterized by the existence of long-lived modes which (presumably) dominate
the decay timescale of the perturbations. We confirm all the main qualitative
features of these slowly-damped modes as predicted by Festuccia and Liu
(arXiv:0811.1033) for the scalar-field (tensor-type gravitational)
fluctuations. However, quantitatively we find dimensional-dependent correction
factors. We also investigate the dependence of the QNM frequencies on the
horizon radius of the black hole (brane) and the angular momentum (wavenumber)
of vector- and scalar-type gravitational perturbations.Comment: 5 pages, RevTex4. v2: References added and minor typos corrected.
Published versio

### Cross section, final spin and zoom-whirl behavior in high-energy black hole collisions

We study the collision of two highly boosted equal mass, nonrotating black
holes with generic impact parameter. We find such systems to exhibit zoom-whirl
behavior when fine tuning the impact parameter. Near the threshold of immediate
merger the remnant black hole Kerr parameter can be near maximal (a/M about
0.95) and the radiated energy can be as large as 35% of the center-of-mass
energy.Comment: Rearranged results section; accepted for publication in Phys. Rev.
Let

### On gravitational-wave spectroscopy of massive black holes with the space interferometer LISA

Newly formed black holes are expected to emit characteristic radiation in the
form of quasi-normal modes, called ringdown waves, with discrete frequencies.
LISA should be able to detect the ringdown waves emitted by oscillating
supermassive black holes throughout the observable Universe. We develop a
multi-mode formalism, applicable to any interferometric detectors, for
detecting ringdown signals, for estimating black hole parameters from those
signals, and for testing the no-hair theorem of general relativity. Focusing on
LISA, we use current models of its sensitivity to compute the expected
signal-to-noise ratio for ringdown events, the relative parameter estimation
accuracy, and the resolvability of different modes. We also discuss the extent
to which uncertainties on physical parameters, such as the black hole spin and
the energy emitted in each mode, will affect our ability to do black hole
spectroscopy.Comment: 44 pages, 21 figures, 10 tables. Minor changes to match version in
press in Phys. Rev.

### A note on the resonant frequencies of rapidly rotating black holes

I discuss the range of validity of Detweiler's formula for the resonant
frequencies of rapidly rotating Kerr black holes. While his formula is correct
for extremal black holes, it has also been commonly accepted that it describes
very well the resonant frequencies of near extremal black holes, and that
therefore there is a large number of modes clustering on the real axis as the
black hole becomes extremal. I will show that this last statement is not only
incorrect, but that it also does not follow from Detweiler's formula, provided
it is handled with due care. It turns out that only the first n <<
-log{(r_+-r_-)/r_+} modes are well described by that formula, which translates,
for any astrophysical black hole, into one or two modes only. All existing
numerical data gives further support to this claim. I also discuss some
implications of this result for recent investigations on the late-time dynamics
of rapidly rotating black holes.Comment: 5 pages, ReVTeX

### Black hole collision with a scalar particle in four, five and seven dimensional anti-de Sitter spacetimes: ringing and radiation

In this work we compute the spectra, waveforms and total scalar energy
radiated during the radial infall of a small test particle coupled to a scalar
field into a $d$-dimensional Schwarzschild-anti-de Sitter black hole. We focus
on $d=4, 5$ and 7, extending the analysis we have done for $d=3$. For small
black holes, the spectra peaks strongly at a frequency $\omega \sim d-1$, which
is the lowest pure anti-de Sitter (AdS) mode. The waveform vanishes
exponentially as $t \to \infty$, and this exponential decay is governed
entirely by the lowest quasinormal frequency. This collision process is
interesting from the point of view of the dynamics itself in relation to the
possibility of manufacturing black holes at LHC within the brane world
scenario, and from the point of view of the AdS/CFT conjecture, since the
scalar field can represent the string theory dilaton, and 4, 5, 7 are
dimensions of interest for the AdS/CFT correspondence.Comment: 16 pages, 13 figures. Published versio

### Inspiral, merger and ringdown of unequal mass black hole binaries: a multipolar analysis

We study the inspiral, merger and ringdown of unequal mass black hole
binaries by analyzing a catalogue of numerical simulations for seven different
values of the mass ratio (from q=M2/M1=1 to q=4). We compare numerical and
Post-Newtonian results by projecting the waveforms onto spin-weighted spherical
harmonics, characterized by angular indices (l,m). We find that the
Post-Newtonian equations predict remarkably well the relation between the wave
amplitude and the orbital frequency for each (l,m), and that the convergence of
the Post-Newtonian series to the numerical results is non-monotonic. To leading
order the total energy emitted in the merger phase scales like eta^2 and the
spin of the final black hole scales like eta, where eta=q/(1+q)^2 is the
symmetric mass ratio. We study the multipolar distribution of the radiation,
finding that odd-l multipoles are suppressed in the equal mass limit. Higher
multipoles carry a larger fraction of the total energy as q increases. We
introduce and compare three different definitions for the ringdown starting
time. Applying linear estimation methods (the so-called Prony methods) to the
ringdown phase, we find resolution-dependent time variations in the fitted
parameters of the final black hole. By cross-correlating information from
different multipoles we show that ringdown fits can be used to obtain precise
estimates of the mass and spin of the final black hole, which are in remarkable
agreement with energy and angular momentum balance calculations.Comment: 51 pages, 28 figures, 16 tables. Many improvements throughout the
text in response to the referee report. The calculation of multipolar
components in Appendix A now uses slightly different conventions. Matches
version in press in PR

### In-situ and laboratory airtightness tests of structural insulated panels (SIPs) assemblies

One of the main factors influencing building airtightness is the construction typology. As building environmental performance requirements raise so does the prevalence of less conventional envelope construction systems as modular structural insulated panels (SIPs) buildings.
In this paper, the airtightness performance of a constructive solution based on SIPs was evaluated. Airtightness tests were performed on the laboratory according to the EN 12114-2000 methodology. One complete exterior wall assembly and another one with the inclusion of a window were tested to determine their performance as an effective air barrier. The impact of the window framing in the overall resistance to air leakage was also determined. Additionally, the airtightness of a dwelling using these SIPs was measured during the construction phase and after commissioning. The objective was not only the assessment of the ACH50 difference between the two stages, but also the comparison with previously tested conventional envelopes on the same climate.
Laboratory and field test data resulted in mismatching values. Workmanship and unforeseen leakage paths were found to be the main contributors to these findings. Moreover, the case study displayed a superior airtightness performance when compared to heavy type construction solutions, common amongst the Portuguese building stock. Additional work is needed to identify and quantify envelope airpaths in order to properly design lightweight buildings solutions. FCT-Fundação para a Ciência e a
Tecnologia, the funding of the Doctoral Grant PD/BD/135162/2017, through the Doctoral
Programme EcoCoRe.
This paper is a result of the project “H0ME ZERO”, with the reference POCI
-01-0247-FEDER-017840, co-funded by the European Regional Development Fund (ERDF), through
the Operational Programme for Competitiveness and Internationalization (COMPETE 2020),
under the PORTUGAL 2020 Partnership Agreement HOME
This work was financially supported by : Project POCI-01-0145-FEDER-007457
-CONSTRUCT -Institute of R&D In Structures and Construction funded by FEDER funds through COMPETE 2020 -Programa Operacional Competitividade e Internacionalização
POCI – and by national funds through -
Fundação para a Ciência e a
Tecnologiainfo:eu-repo/semantics/publishedVersio

### Quasinormal ringing of Kerr black holes: The excitation factors

Distorted black holes radiate gravitational waves. In the so-called ringdown
phase radiation is emitted in a discrete set of complex quasinormal
frequencies, whose values depend only on the black hole's mass and angular
momentum. Ringdown radiation could be detectable with large signal-to-noise
ratio by the Laser Interferometer Space Antenna LISA. If more than one mode is
detected, tests of the black hole nature of the source become possible. The
detectability of different modes depends on their relative excitation, which in
turn depends on the cause of the perturbation (i.e. on the initial data). A
``universal'', initial data-independent measure of the relative mode excitation
is encoded in the poles of the Green's function that propagates small
perturbations of the geometry (``excitation factors''). We compute for the
first time the excitation factors for general-spin perturbations of Kerr black
holes. We find that for corotating modes with $l=m$ the excitation factors tend
to zero in the extremal limit, and that the contribution of the overtones
should be more significant when the black hole is fast rotating. We also
present the first analytical calculation of the large-damping asymptotics of
the excitation factors for static black holes, including the Schwarzschild and
Reissner-Nordstrom metrics. This is an important step to determine the
convergence properties of the quasinormal mode expansion.Comment: 33 pages, 9 figures, 7 tables, RevTeX4. v2: Two new figures and minor
changes in the presentation. Matches version in press in Phys. Rev.

### Reliability of quantitative and qualitative assessment of air leakage paths through reductive sealing

A full characterization of a building air leakage is labour intensive. As results of laboratory and mock-up experimentation rarely portray in situ conditions, the assessment of real case studies bring added value. Still, the results of experimentation of the latter face more challenges than the former. In this work a full quantitative and qualitative assessment of air leakage paths is performed, using a light steel framing (LSP) modular building with structural insulated panels (Sips) as case study. Blower-door measurements undergo for a sealing campaign of eleven steps, a technique often described as reductive sealing. Additionally, smoke tracer measurements were carried out to visually identify the air leakage locations. The application of three regression methods resulted in different uncertainty estimates. Less than 7% of the total air leakage was not attributed to one of the considered types of air leakage paths. Assessing less impacting leakage paths first and placing similar types of air leakage paths in a consecutive sealing order seems to be the most correct strategy when using the reductive sealing technique. On average, at a reference pressure difference of 4 Pa, the sealing step uncertainty averaged, 9.9%, 18.8%, and 27.5%, depending on the method used for regression of the blower door test results. Despite the highest calculated uncertainty, literature shows that the application of the method leading to it, Weighted Line of Organic Correlation (WLOC), provides the results in closer agreement with the observed uncertainty of measurements.- This work was financially supported by: Base Funding - UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT-Instituto de 1&0 em Estruturas e Construcoes - funded by national funds through the FCT/MCTES (PIDDAC). The author would like to acknowledge the support of FCT - Fundacao para a Ciencia e a Tecnologia, the funding of the Doctoral Grant PD/BDIl35162/2017, through the Doctoral Programme EcoCoRe

- …