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.
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.
On September 14th and December 26th, 2015, the Advanced LIGO detectors observed two gravitational wave signals, each from the merger of stellar-mass black holes. These two observations have given us the first glimpse in to the population of stellar mass black holes. In this talk I will discuss these first detections of gravitational waves including the non-detection of gravitational waves from the merger of binary neutron star and neutron star black holes systems.
LIGO's first observing run which ended in January 2016 yielded two unambiguous gravitational wave signals (GW150914 and GW151226) from the merger of binary black holes as well as a possible third signal (LVT151012). I will review our current estimates of the parameters of the source systems as well as possible formation scenarios. I will discuss how joint analyses of GW150914 and GW151226 allow us to place bounds on departures from general relativity, infer astrophysical binary black hole formation rates, and constrain the mass distribution of coalescing black hole systems.
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.