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.
We reconsider a gauge theory of gravity in which the gauge group is the conformal group SO(4,2), and the action is of the Yang-Mills form, quadratic in the curvature. The vacuum sector of the resulting gravitational theory exhibits local conformal symmetry. We allow for conventional matter coupled to the spacetime metric as well as matter coupled to the field that gauges special conformal transformations. When the theory is linearized about flat space, we find there is a long range gravitational force in addition to Newton’s inverse square law.
Aretakis' discovery of a horizon instability of extremal black holes came as something of a surprise given earlier proofs that individual frequency modes are bounded. Is this kind of instability invisible to frequency-domain analysis? The answer is no: We show that the horizon instability can be recovered in a mode analysis as a branch point at the horizon frequency. We use the approach to generalize to nonaxisymmetric gravitational perturbations and reveal that certain Weyl scalars are unbounded in time on the horizon.
Improving the broadband quantum sensitivity of an advanced gravitational wave detector is one of the key steps for future updating of gravitational wave detectors. Reduction of the broadband quantum noise needs squeezed light with frequency dependent squeezing angle. Current designs for generating frequency dependent squeezed light are based on an ultra-high finesse filter cavity, therefore optical loss will serious contaminate the squeezed light.
Questions of nonlinear stability in global AdS space have recently received a significant amount of attention, both as an interesting problem in mathematical general relativity and nonlinear dynamics, and in relation to thermalization studies within the AdS/CFT paradigm. Working with nonlinear perturbation theory (the main technique available for analytic studies in this area) requires a thorough understanding of the properties of linearized AdS fields'
Current observations provide precise but limited information about inflation and reheating. Theoretical considerations, however, suggest that the early universe might be filled with a large number of interacting fields with unknown interactions. How can we quantitatively understand the dynamics of perturbations during inflation and reheating in such scenarios and when only limited
constraints are available from observations? Based on a precise
Inspired by recent progress into recasting dissipative fluid dynamics within an effective action formalism,
I will show how to embed this problem in holography, where such effective actions can be computed explicitly for the class of relativistic conformal fluids. In particular I will identify the geometric counterpart of certain Goldstone bosons, the light degrees of freedom responsible for the low energy excitations in hydrodynamics. Moreover I will show how the underlying UV Schwinger-Keldysh structure arises at the level of the effective action.
The Advanced LIGO observatories have successfully completed their first science run. Data were collected from September 2015 to January 2016, with a sensitivity a few times better than initial instruments in the hundreds of Hertz band. In this talk I will describe the searches for gravitational-wave transients performed during the first few weeks of the science run. Furthermore, I will describe the methods devised to characterize transient gravitational-wave sources and their applications in the advanced gravitational-wave detector era.
Generation of accurate mock observations tailored specifically to upcoming surveys such as Advanced ACT, CHIME, and LSST is a key technical challenge in cosmology. Traditional approaches involving N-body simulation are fraught with difficulties due to increasingly large survey volumes and depths. Typically, statistical ensembles can only be realized for a few carefully-chosen parameters, limiting exploration to a significantly restricted cosmological model space.
In the coming years, astrophysical observations of strongly gravitating systems will provide us with exciting new data to study extremely compact objects and Einstein’s theory of general relativity. In particular, gravitational wave observatories will soon reach the sensitivity required to detect merging black holes and neutron stars, while the Event Horizon Telescope is about to observe accretion flows around two supermassive black holes with sub-horizon resolution.
The mergers of black hole-neutron star and neutron star-neutron star binaries are one of the primary targets for Advanced LIGO and other gravitational wave detectors now coming online. In addition, these events may source a number of electromagnetic counterparts, including short gamma-ray bursts and ejecta powered transients. Particularly in the case of binaries that are dynamically-assembled in dense stellar regions like globular clusters, these mergers may involve neutron stars with non-negligible spin.