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# Strong Gravity

This series consists of talks in areas where gravity is the main driver behind interesting or peculiar phenomena, from astrophysics to gravity in higher dimensions.

## Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

## Numerical Relativity on Constant Mean Curvature Hypersurfaces

Jeudi oct 13, 2011
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Constant mean curvature (uniform K) hypersurfaces extend to future null infinity in asymptotically flat spacetimes. With conformal compactification, the entire hypersurface can be covered by a finite spatial grid, eliminating any need an "outgoing wave" boundary condition or for extrapolation to find gravitational wave amplitudes. I will discuss the asymptotic behavior near future null infinity, how this can be simplified by suitable gauge conditions, and how this determines the physical Bondi energy and momentum of the system.

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## Low Metallicity Star Formation: a Nursery for Compact Binary Mergers?

Jeudi oct 06, 2011

Most predictions for binary compact object formation are normalized to the present-day Milky Way population. In this talk, I suggest the merger rate of black hole binaries could be exceptionally sensitive to the ill-constrained fraction of low-metallicity star formation that ever occurred on our past light cone. I discuss whether and how observations might distinguish binary evolution uncertainties from this strong trend, both in the near future with well-identified electromagnetic counterparts and in the more distant future via third-generation gravitational wave detectors.

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## Corrections to the Apparent Value of the Cosmological Constant Due to Local Inhomogeneities

Jeudi sep 29, 2011
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Supernovae observations strongly support the presence of a cosmological constant, but its value, which we will call apparent, is normally determined assuming that the Universe can be accurately described by a homogeneous model. Even in the presence of a cosmological constant we cannot exclude nevertheless the presence of a small local inhomogeneity which could affect the apparent value of the cosmological constant.

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## Metabolic Pathways for Gamma-Ray Bursts

Jeudi juil 28, 2011
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There is now a consensus that gamma-ray bursts involve
extraordinary power outputs, and highly relativistic dynamics.
The trigger is probably a binary merger or collapse involving
compact objects. The most plausible progenitors, ranging from
NS-NS mergers to various hypernova-like scenarios, eventually
lead to the formation of a black hole with a debris torus around it.
The various modes of energy extraction from such systems are discussed.

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## Testing the Nature of Black Hole Candidates

Jeudi juil 21, 2011
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Today there is robust observational evidence of dark and compact objects in X-ray binary systems with a mass of 5-20 $M_\odot$ and in galactic nuclei with a mass of $10^5 - 10^9$ $M_\odot$. The conjecture is that all these objects are the Kerr black holes predicted by General Relativity, as they cannot be explained otherwise without introducing new physics. However, there are no directs observational evidences. In this talk, I discuss how the Kerr black hole hypothesis can be tested with present and future X-ray data and the current constraints on the nature of this objects.

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## The Pioneer Anomaly: Known and Unknown Unknowns

Jeudi mai 26, 2011
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TBA

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## Modeling the evaporation of mini black holes

Vendredi mai 06, 2011

TeV-scale models of quantum gravity predict the formation of mini black holes at the Large Hadron Collider. If these black holes can be treated, at least for part of their evolution, as semi-classical objects, they will emit Hawking radiation. In this talk we review the modeling of this evaporation process, particularly for the case when the black hole is rotating. A detailed understanding of the Hawking radiation is necessary for accurate simulations of black hole events at the LHC.

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## Cross-Correlation Methods in Continuous Gravitational-Wave Searches

Jeudi avr 14, 2011
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Cross-correlation of gravitational-wave (GW) data streams has been used to search for stochastic backgrounds, and the same technique was applied to look for periodic GWs from the low-mass X-ray binary (LMXB) Sco X-1. Recently a technique was developed which refines the cross-correlation scheme to take full advantage of the signal model for periodic gravitational waves from rotating neutron stars. By varying the time window over which data streams are correlated, the search can "trade off" between parameter sensitivity and computational cost.

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## Cauchy horizon (in)stability in spherically symmetric self-similar gravitational collapse.

Jeudi avr 07, 2011
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Various self-similar spherically symmetric spacetimes admit naked singularities, providing a challenge to the cosmic censorship hypothesis. However, it is not clear if the naked singularities are artefacts of the high degree of symmetry of the spacetimes, or if they are potentially generically present. To address this question, we consider perturbations of (various cases of) these spacetimes, focusing particularly on the behaviour of the perturbations as they impinge on the Cauchy horizon.

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## Gravitational wave phenomenology for LIGO, LISA and co from effective field theories

Jeudi mar 31, 2011
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The effective field theory framework yields a systematic treatment of gravitational bound states such as binary systems. Gravitational waves emitted from compact binaries are one of the prime event candidates at direct detection experiments. Due to the multiple scales involved in the binary problem, an effective field theory treatment yields many advantages in perturbative calculations. My talk will review the setup of the effective field theory framework and report on recent progress in gravitational wave phenomenology.

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## RECENT PUBLIC LECTURE

### Pauline Gagnon: Improbable Feats and Useless Discoveries

Speaker: Pauline Gagnon