GRAVITY THEORY SEMINARS 2008
Abstracts:
Thurs., Feb. 14, 4:00pm, Room 1201
Juan Maldacena, Institute for Advanced Study
``AdS/CFT duality: recent developments''
TBA
Thurs., Feb. 28, 2:00pm, Room 4102
Sam Waldman, LIGO Caltech
``Enhancing and Advancing LIGO: 4 years of detector upgrades''
After successfully completing 1 year of coincident data taking at design sensitivity, commissioning has begun on the Enhanced LIGO upgrades to the 4 km detectors. The incremental upgrades, including increased power to 35~W and a new DC readout scheme, are designed to achieve a factor of 2+ improvement in sensitivity while validating key Advanced LIGO technologies. The Advanced LIGO program begins commissioning in 2010, implementing a new optical scheme, higher power, and improved seismic isolation. Together, these improvements will increase the sensitive band to 10 - 1,000~Hz, improve the strain sensitivity to ~< 4 * 10^{-24} Hz^ {-1/2}, and extend the NS/NS inspiral range to 170~Mpc.
Thurs., Mar. 6, 2:00pm, Room 4102
Etienne Racine, University of Maryland
``Gaussianity of LISA's confusion background''
Data analysis for the proposed Laser Interferometer Space Antenna (LISA) will be complicated by the huge number of sources in the LISA band. Throughout much of the band, galactic white dwarf binaries (GWDBs) are sufficiently dense in frequency space that it will be impossible to resolve most of them, and "confusion noise" from the unresolved Galactic binaries will dominate over instrumental noise in determining LISA's sensitivity to other sources in that band. Confusion noise from unresolved extreme-mass-ratio inspirals (EMRIs) could also contribute significantly to LISA's total noise curve. To date, estimates of the effect of LISA's confusion noise on matched-filter searches and their detection thresholds have generally approximated the noise as Gaussian, based on the Central Limit Theorem. However in matched-filter searches, the appropriate detection threshold for a given class of signals may be located rather far out on the tail of the signal-to-noise probability distribution, where a priori it is unclear whether the Gaussian approximation is reliable. Using the Edgeworth expansion and the theory of large deviations, we investigate the probability distribution of the usual matched-filter detection statistic, far out on the tail of the distribution. We apply these tools to four somewhat idealized versions of specific LISA searches.
Thurs., Mar. 13, 4:00pm, Room 1201
Alex Maloney, McGill University
``Phases of Quantum Gravity in Three Dimensions''
Quantum gravity in a world with three dimensions (that is, with two spatial dimensions and one time dimension) provides a fascinating theoretical laboratory where we can test precisely our ideas about quantum general relativity. This theory has the remarkable property that when the cosmological constant is negative Einstein's theory of gravity can -- with a little help from string theory -- be quantized. So we can begin to understand the structure of space-time beyond the classical approximation. Many objects which appear quite mysterious, such as black holes and big bang or big crunch singularities, can be understood precisely at the quantum level. The Lee-Yang theory of phase transitions and the monster group both make appearances in this story.
Fri., Mar. 14, 3:30pm, Room 4102
Alex Maloney, McGill University
``The Sum Over Geometries in Three Dimensions''
We consider pure three-dimensional quantum gravity with a negative cosmological constant. The sum of known contributions to the partition function from classical geometries can be computed exactly, including quantum corrections. However, the result is not physically sensible, and if the model does exist, there are some additional contributions. One possibility is that complex geometries need to be included, leading to a holomorphically factorized partition function. We analyze the subleading corrections to the Bekenstein-Hawking entropy and show that these can be correctly reproduced in such a holomorphically factorized theory. We also consider the Hawking-Page phase transition between a thermal gas and a black hole and show that it is a phase transition of Lee-Yang type, associated with a condensation of zeros in the complex temperature plane. Finally, we analyze pure three-dimensional supergravity, with similar results.
Thurs., Mar. 27, 2:00pm, Room 4102
Dierdre Shoemaker, Pennsylvania State University
``Binary Black Hole Encounters, Bursts and Maximal Spin''
I present results from a series of numerical relativity investigations of binary black hole encounters ranging from almost direct infall to numerous orbits before infall. These encounters exhibit multiple bursts of radiation in the merger process that may be relevant to gravitational wave observations. In addition to these bursts of radiation, we studied the spin of the final black hole, an important parameter in astrophysical processes involving black holes. The final spin in the coalescence of non-spinning black holes is determined by the ``residual'' orbital angular momentum of the binary. This residual momentum consists of the orbital angular momentum that the binary is not able to shed in the process of merging. Our results show that there is a maximum rate of spin per mass of the final black hole and when that maximum occurs in terms of the orbital angular momentum.
Thurs., Apr. 3, 4:00pm, Room 1201
Richard Easther, Yale University
``The Observational Fingerprints of Inflation''
Inflation ensures that the early universe is homogeneous and isotropic, and generates small perturbations whose amplitude is almost independent of their wavelength. However, we know very little about the physical mechanism that drives the inflationary era, and there are many competing proposals. Since inflation renders the early universe almost featureless, the differences between inflationary scenarios are necessarily small, but will be of crucial importance when testing competing models. I will first describe how several key predictions of inflation have been tested and verified by cosmological observations. I will then discuss possible ``fingerprints'' of specific inflationary models, including the detailed form of the primordial perturbation spectrum, gravitational waves (produced both during and immediately after inflation), and primordial fluctuations with non-Gaussian statistics, and the possibility of exploiting these in upcoming and proposed experiments.
Thurs., Apr. 10, 2:00pm, Room 4102
Thomas Sotiriou, University of Maryland
``f(R) Gravity''
Modified gravity theories have received increased attention lately due to combined motivation coming from both high-energy physics and cosmology and astrophysics. Among numerous alternatives to Einstein's theory of gravity, theories which include higher order curvature invariants, and specifically the particular class of f(R) theories, have a long history. In the last 5 years there has been a new stimulus for their study, leading to a number of interesting results. An introduction to f(R) theories of gravity will be given and their consequences and constraints will be discussed.
Thurs., Apr. 17, 2:00pm, Room 4102
Sergei Dubovsky, Harvard University
``Superluminal travel in two dimensions''
TBA
Tues., Apr. 22, 2:00pm, Room 1201
Joseph Samuel, Raman Research Institute
``Surface tension and the cosmological constant''
One of the few predictions from quantum gravity models is Sorkin's observation that the cosmological constant has quantum fluctuations originating in the fundamental discreteness of spacetime at the Planck scale. Here we present a compelling analogy between the cosmological constant of the universe and the surface tension of fluid membranes. The discreteness of spacetime on the Planck scale translates into the discrete molecular structure of a fluid membrane. We propose an analog quantum gravity experiment which realises Sorkin's idea in the laboratory. We also notice that the analogy sheds light on the cosmological constant problem, suggesting a mechanism for dynamically generating a vanishingly small cosmological constant. We emphasize the generality of Sorkin's idea and suggest that similar effects occur generically in quantum gravity models.
Thurs., Apr. 24, 4:00pm, Room 1201
W.G Unruh, University of British Columbia
``Where do the particles come from?''
When Hawking discovered black hole evaporation, the quantum emission of particles by black holes, left open was the origin of the particles. He presented the picture of pair creation, of virtual particle pairs ripped apart by the gravitiational field near the horizon, but no calculation to support this picture. Instead the closest picture was of a horizon splitting at absurdly high energies (trans Plankian problem). Using dumb holes, the acoustic or other analog of black holes, I will argue, both numerically and analytically, that the creation process is a low energy process which happens well outside the horizon.
Thurs., May 8, 2:00pm, Room 4102
Eric Poisson, University of Guelph
``The gravitational self-force''
The gravitational self-force describes the effects of a particle's own field on its motion. While the motion is geodesic in the test-mass limit, for a finite-mass body the gravitational perturbation created by the body produces an acceleration, and the object is said to move under the influence of its own self-force. I will first describe the astrophysical context of the work now being done to compute the gravitational self-force. Next I will review the foundations of the self-force, and describe how to obtain the equations of motion for a small black hole moving in an external universe. This calculation produces a prescription that can be applied to the case of point particles, and I will explain how an infinite retarded field can be unambiguously decomposed into a singular piece that exerts no force, and a smooth remainder that is responsible for the acceleration. I will describe the recent effort, by a number of workers, to compute the self-force in the case of a small mass moving in the field of a much more massive black hole. And finally, I will discuss open issues and future work.
Mon., May 19, 2:00pm, Room 4102
James Overduin, University of Waterloo / Stanford University
``From Gravity Probe B to STEP: Testing Einstein in Space''
TBA
| Home People Ph.D. Program Seminars Available Positions Related Links |
|---|
|
Back to the UM Physics
Department Home Page
 |
Back to the University
of Maryland Home Page
 |