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.
Gravitational wave astronomy provides an unprecedented opportunity to test the nature of black holes and search for exotic, compact alternatives. Recent studies have shown that exotic compact objects (ECOs) can ring down in a manner similar to black holes, but can also produce a sequence of distinct pulses resembling the initial ringdown. These “echoes” would provide definite evidence for the existence of ECOs. In this work we study the generation of these echoes in a generic, parameterized model for the ECO, using Green’s functions.
Abstract TBA
Models of gravitational waveforms play a critical role in detecting and characterizing the gravitational waves (GWs) from compact binary coalescences. Waveforms from numerical relativity (NR), while highly accurate, are too computationally expensive to produce to be directly used in parameter estimation. We propose a Gaussian process regression (GPR) method to generate accurate reduced-order-model waveforms based only on existing accurate (e.g. NR) simulations.
The characteristics of black holes smaller than the Planck scale are addressed. These result from a modified metric that reproduces desirable aspects of a variety of disparate models in the sub-Planckian limit, while remaining Schwarzschild in the large mass limit. The self-dual nature of this solution has two interesting features: first, it naturally implies the Generalized Uncertainty Principle. Secondly, this metric exhibits an effective dimensional reduction feature, indicating that the gravitational physics of the sub-Planckian regime is effectively (1+1)-D.
We will discuss how the process of superradiance, combined with
gravitational wave measurements, makes black holes into
nature's laboratories to search for new light bosons. We will present
analytic results for superradiance of light vector (spin-1) particles,
valid in the regime where the vector's Compton wavelength is much
larger than the horizon size of a black hole. If superradiance is
efficient, the occupation number of the vectors in the black hole's
vicinity grows exponentially and the black hole spins down. We will
The modeling of pulsar radio and gamma-ray emission suggests that in order to interpret the observations one needs to understand the field geometry and the plasma state in the emission region. In recent years, significant progress has been achieved in understanding the magnetospheric structure in the limit of abundant plasma supply. However, the very presence of dense plasma everywhere in the magnetosphere is not obvious. Even the region where the observed emission is produced is subject to debate.
The first detections of gravitational waves by LIGO-Virgo initiated the era of Gravitation-Wave Astronomy. Gravitational-waves serve as a new and independent probe of the Universe. In addition, the combination of gravitational-waves with information from other messengers, such as electromagnetic emission from the same source, will lead to a more complete and accurate understanding of cosmology and astrophysics. In this talk, I will discuss some interesting learnings from the Advanced LIGO-Virgo first observing run and several scientific goals we expect to reach in the next few years.
The anti-de Sitter (AdS) space is of great interest in contemporary
theoretical physics due to the AdS/CFT correspondence. However, the
question of stability of AdS space is unanswered till now. After
giving the motivation for studies of asymptotically AdS spaces, I will
review dynamics of such spacetimes in the context of AdS instability
problem. This survey will include: evidence for instability of AdS
space, existence and properties of time-periodic solutions, and
Massive objects orbiting a near-extreme Kerr black hole plunge into the horizon after passing the innermost stable circular orbit, producing a potentially observable signal of gravitational radiation. The near horizon dynamics of such rapidly rotating black holes is governed by a conformal symmetry. In the talk I will show how this symmetry can be exploited to analytically compute the gravitational waves produced by a variety of orbits. I will also discuss an application to gravitational self-force and comment on the holographic interpretation of the process.
Galaxy mergers are a standard aspect of galaxy formation and evolution, and most (likely all) large galaxies contain supermassive black holes. As part of the merging process, the supermassive black holes should in-spiral together and eventually merge, generating a background of gravitational radiation in the nanohertz to microhertz regime. Processes in the early Universe such as relic gravitational waves and cosmic strings may also generate gravitational radiation in the same frequency band.