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. http://pirsa.org/podcast/S020 Science 2012 http://blogs.law.harvard.edu/tech/rss en-ca Tue, 22 May 2012 06:41:50 -0400 sbradwell@perimeterinstitute.ca Tue, 22 May 2012 06:41:50 -0400 G 180 sbradwell@perimeterinstitute.ca Steve Bradwell's - Podcast Generator The uncertainty in the equation of state of cold matter above nuclear density is notorious. Despite four decades of neutron-star observations, recent observational estimates of neutron-star radii still range from 8 to 16 km; the pressure above nuclear density is not known to better than a factor of 5; and one cannot yet rule out the possibility that the ground state of cold matter at zero pressure might be strange quark matter -- that the term "neutron star" is a misnomer for strange quark stars. The last few orbits of binary inspiral are sensitive to the stars' distortion, and a major goal of the next generation of gravitational wave detectors is to extract parameters characterizing the high-density equation of state from inspiral waveforms. This talk reports a first study that uses numerical simulations to estimate the accuracy with which the equation of state can be measured. John Friedman http://streamer.perimeterinstitute.ca/mp3/c81c6da5-bc0f-4d38-a4ef-c681fb04943f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c81c6da5-bc0f-4d38-a4ef-c681fb04943f.mp3 Thu, 24 Sep 2009 13:40:00 -0400 With the imminent detection of gravitational waves by ground-based interferometers, such as LIGO, VIRGO and TAMA, pulsar timing observations, and proposed space-borne detectors, such as LISA, we must ask ourselves: how much do we trust general relativity? The confirmation of general relativity through Solar System experiments and binary pulsar observations has proved its validity in the weak-field, where velocities are small and gravity is weak, but no such tests exist in the strong, dynamical regime, precisely the regime of most interest to gravitational wave observations. Unfortunately, because of their inherent feebleness, the extraction of gravitational waves from detector noise relies heavily on the technique of matched filtering, where one constructs waveform filters or templates to clean the data. Currently, all such waveforms are constructed with the implicit assumption that general relativity is correct both in the weak and strong, dynamical regimes. Such an assumption constitutes a fundamental bias that will introduce a systematic error in the detection and parameter estimation of signals, and in turn can lead to a mischaracterization of the universe through incorrect inferences about source event rates and populations. In this talk, I will define this bias, explain its possible consequences and propose a remedy through a new scheme: the parameterized post-Einsteinian framework. In this framework one enhances waveforms via the inclusion of post-Einsteinian parameters that both interpolate between general relativity and well-motivated alternative theories, but also extrapolate to unknown theories, following sound theoretical principles, such as consistency with conservation laws and symmetries. The parametrized post-Einsteinian framework should allow matched filtered data to select a specific set of post-Einsteinian parameters without {emph{a priori}} assuming the validity of the former, thus allowing the data to either verify general relativity or point to possible dynamical strong-field deviations. Nicolas Yunes http://streamer.perimeterinstitute.ca/mp3/6960130a-9891-4c71-b45a-de8702d64a76.mp3 Science http://streamer.perimeterinstitute.ca/mp3/6960130a-9891-4c71-b45a-de8702d64a76.mp3 Thu, 08 Oct 2009 13:40:00 -0400 I present an overview of how inspiral-merger-ringdown (IMR) waveforms are currently being used within LIGO and Virgo search efforts. I'll discuss search strategies from the two major astrophysics working groups within t he LIGO/Virgo collaboration searching for transient gravitational-wave signals - the Compact Binary Coalescence group and the Burst Group. For masses where the inspiral, merger and ring-down phases are prominent in the LIGO/Virgo band both working groups have developed pipelines that are sensitive to these systems and are now trying to work together to make a joint statement about LIGO and Virgo's sensitivity to IMR systems. Chad Hanna http://streamer.perimeterinstitute.ca/mp3/8d21698e-e6b3-4435-a8b0-c5265a56114a.mp3 Science http://streamer.perimeterinstitute.ca/mp3/8d21698e-e6b3-4435-a8b0-c5265a56114a.mp3 Thu, 05 Nov 2009 13:40:00 -0500 TBA Misha Smolkin http://streamer.perimeterinstitute.ca/mp3/8db37e91-db48-436f-af0e-fc52c2332a10.mp3 Science http://streamer.perimeterinstitute.ca/mp3/8db37e91-db48-436f-af0e-fc52c2332a10.mp3 Thu, 26 Nov 2009 13:40:00 -0500 Misha Smolkin http://streamer.perimeterinstitute.ca/mp3/39400350-cdbd-44b1-ac22-a2b4ea9d2ded.mp3 Science http://streamer.perimeterinstitute.ca/mp3/39400350-cdbd-44b1-ac22-a2b4ea9d2ded.mp3 Thu, 03 Dec 2009 15:00:00 -0500 One of the main science objectives for the Laser Interferometer Space Antenna (LISA) is to quantitatively map the strong field regions around compact objects using Extreme-Mass-Ratio Inspirals (EMRIs). This idea has been shown to be possible in principle, however in practice only inspirals in a Kerr spacetime have been studied in detail. A spacetime mapping algorithm for an EMRI inspiral into a generic compact object is formulated using ideas from integrable systems. I discuss several aspects of the theoretical development required to make the problem tractable. Some recent results about particle orbits around "Bumpy Black" holes are highlighted. Jeandrew Brink http://streamer.perimeterinstitute.ca/mp3/25785294-aaeb-42ad-a5cf-4e43cab1a191.mp3 Science http://streamer.perimeterinstitute.ca/mp3/25785294-aaeb-42ad-a5cf-4e43cab1a191.mp3 Fri, 04 Dec 2009 12:00:00 -0500 In quantum field theory it is possible to create negative local energy densities. This would violate the Generalized Second Law (GSL) unless there is some sort of energy condition requiring the negative energy to be counterbalanced by positive energy. TO explore what this energy condition is, I will assume that the GSL holds in semiclassical gravity for all future causal horizons. From CPT symmetry it follows that the time-reverse of the GSL, properly understood, holds for all past causal horizons. These two conditions together then imply that the Averaged Null Energy Condition (ANEC) holds on any null line, i.e. a complete achronal lightlike null geodesic. In curved spacetimes, the ANEC can be violated on general geodesics. But even if the ANEC only holds on null lines, theorems by Sorkin, Penrose and Woolgar, and by Graham and Olum imply that semiclassical gravity should satisfy positivity of energy, topological censorship, and should not admit closed timelike curves. These results can thus be seen as consequences of the GSL. However, these theorems don't apply when gravitational fluctuations are taken into account. In that case, the GSL argument suggests a modification to the ANEC which may make these theorems applicable to perturbative quantum gravity. Aron Wall http://streamer.perimeterinstitute.ca/mp3/a2851fcf-50e4-4438-aa6a-6fe9e8df1dda.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a2851fcf-50e4-4438-aa6a-6fe9e8df1dda.mp3 Thu, 10 Dec 2009 15:00:00 -0500 Einstein’s general theory of relativity is the standard theory of gravity, especially where the modern needs of astronomy, astrophysics, cosmology and fundamental physics are concerned. As such, this theory is used for many practical purposes involving spacecraft navigation, geodesy, time transfer and etc. Series of recent experiments have successfully tested general relativity to a remarkable precision. Various experimental techniques were used to test relativistic gravity in the solar system namely spacecraft Doppler tracking, planetary ranging, lunar laser ranging, dedicated gravity experiments in space and many ground-based efforts. We will discuss the recent progress in the tests of relativistic gravity and motivation for the new generation of high-accuracy gravitational experiments in space. We also discuss the advances in our understanding of fundamental physics that are anticipated in the near future and evaluate the discovery potential of the recently proposed solar system gravitational experiments. Slava Turyshev http://streamer.perimeterinstitute.ca/mp3/b343a109-f347-4595-bed1-2c98d3ca3bd2.mp3 Science http://streamer.perimeterinstitute.ca/mp3/b343a109-f347-4595-bed1-2c98d3ca3bd2.mp3 Thu, 28 Jan 2010 13:00:00 -0500 Binary neutron stars are among the most important sources of gravitational waves which are expected to be detected by the current or next generation of gravitational wave detectors, such as LIGO and Virgo, and they are also thought to be at the origin of very important astrophysical phenomena, such as short gamma-ray bursts. In order to describe the dynamics of these events one needs to solve the full set of general relativistic magnetohydrodynamics equations through the use of parallel numerical codes. I will report on some recent results obtained with the use of the fully general relativistic magnetohydrodynamic code Whisky in simulating binary neutron stars which inspiral and merge forming an hypermassive neutron star which eventually collapses to form a black hole surrounded by a torus. I will in particular describe how mass, equation of state and magnetic fields can affect the dynamics and consequently the gravitational waves emitted by these systems and discuss about their possible connection with the formation of short gamma ray bursts. Bruno Giacomazzo http://streamer.perimeterinstitute.ca/mp3/e82e143e-34b0-4412-aabe-3b353995118a.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e82e143e-34b0-4412-aabe-3b353995118a.mp3 Thu, 25 Feb 2010 13:00:00 -0500 Galaxy mergers, which are a natural consequence of hierarchical assembly of galaxies, are expected to produce binary black holes, which subsequently merge. The detection and analysis of gravitational waves from these sources is the major aim of the next generation gravitational wave detector: LISA, the Laser Interferometric Space Antenna. These gravitational waves encode a tremendous amount of information, but to make the connection with astrophysics and cosmology, it is necessary to identify the galaxies hosting these mergers via the associated electromagnetic counterpart to these mergers. I will describe these mergers events and discuss the various regimes where potential electromagnetic counterparts can be found. I will also describe some recent work, which holds much promise for the prompt identification of these mergers -- an electromagnetic precursor from tidal forcing. Philip Chang http://streamer.perimeterinstitute.ca/mp3/8d8f9581-8fe1-492d-aea5-e05695a43e4e.mp3 Science http://streamer.perimeterinstitute.ca/mp3/8d8f9581-8fe1-492d-aea5-e05695a43e4e.mp3 Thu, 11 Mar 2010 13:00:00 -0500 Gas accretion onto black holes is thought to power some of the most energetic astrophysical phenomena observed. Black hole accretion disks are efficient engines for converting binding energy into light, and for launching relativistic unbound flows (jets) such as in gamma ray bursts, microquasars and radio-loud active galactic nuclei (AGN). Some systems individually exhibit a wide variety of spectral and bolometric states while others remain remarkably predictable. As their brightest emission usually emanates near the black hole's event horizon, they serve as excellent environments for exploring different theories of gravity or for constraining the black hole's geometry. In this talk I will explain how investigators use modern general relativistic magnetohydrodynamic computer simulations to understand accretion observations and probe the strong-field regime of gravity. In particular, I will focus on three topics. First, I will describe how dynamical models of the accretion flow around Sagittarius A*, the supermassive black hole at the center of our galaxy, can help us predict what we will see when observations at the sub-horizon scale are made soon for the first time. Second, I will explain recent developments in simulating cooled thin disks and how their results may affect estimates of black hole spin from the disks' thermal spectra. Last, I will describe how temporal variability analysis of our dynamical simulations can offer insight into the common behavior seen in high-energy emission from black holes with masses of 10 solar masses to a billion solar masses. Scott Noble http://streamer.perimeterinstitute.ca/mp3/30a07dc5-cc22-4e4a-b1ca-8c028ce3a78e.mp3 Science http://streamer.perimeterinstitute.ca/mp3/30a07dc5-cc22-4e4a-b1ca-8c028ce3a78e.mp3 Thu, 25 Mar 2010 13:00:00 -0400 TBA Juan Maldacena http://streamer.perimeterinstitute.ca/mp3/e336c37f-a556-49e0-851d-63a01d44efb7.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e336c37f-a556-49e0-851d-63a01d44efb7.mp3 Thu, 01 Apr 2010 13:00:00 -0400 For the past century, there has been much discussion and debate about the equations of motion satisfied by a classical point charge when the effects of its own electromagnetic field are taken into account. Derivations by Abraham (1903), Lorentz (1904), Dirac (1938) and others suggest that the "self-force" (or "radiation reaction force") on a point charge is given in the non-relativistic limit by a term proportional to the time derivative of the acceleration of the charge. However, the resulting equations of motion then become third order in time, and they admit highly unphysical "runaway" solutions. During the past century, there also has been much discussion and debate about the interpretation of these equations of motion and the conditions that can/should be imposed to eliminate the runaway behavior. We argue that the above difficulties stem from that fact that the usual notion of a point charge is mathematically ill defined. However, a mathematically rigorous notion of a point charge arises in a perturbative description of a body if one considers a limit wherein not only the size of a body but its charge and mass go to zero in an asymptotically self-similar manner. We show how the Abraham-Lorentz-Dirac self-force then arises in a perturbative description of the body's motion, but does not give rise to runaway behavior. As a biproduct of this work, we also rigorously derive dipole forces and resolve some paradoxes of elementary physics, such as how a magnetic dipole placed in a non-uniform magnetic field can gain kinetic energy despite the fact that the magnetic field can "do no work" on the body. Robert Wald http://streamer.perimeterinstitute.ca/mp3/25a1c4a3-d000-4960-8c21-2fb8270a0ba5.mp3 Science http://streamer.perimeterinstitute.ca/mp3/25a1c4a3-d000-4960-8c21-2fb8270a0ba5.mp3 Mon, 05 Apr 2010 16:30:00 -0400 Coincident detections of electromagnetic and gravitational wave signatures from the merger of supermassive binary black holes are the next observational grand challenge. Such detections will provide a wealth of opportunities to study gravitational physics, accretion physics, and cosmology. Understanding the conditions under which coincidences of electromagnetic and gravitational wave signatures arise during supermassive black hole mergers is therefore of paramount importance, requiring multi-scale/physics computational modeling. I will given an overview of these numerical studies and in particular focus on our effort to model the merger of supermassive black hole binaries in the presence of gaseous environments. Pablo Laguna http://streamer.perimeterinstitute.ca/mp3/5ab9d328-02ee-482f-9c88-e1c8ae540c69.mp3 Science http://streamer.perimeterinstitute.ca/mp3/5ab9d328-02ee-482f-9c88-e1c8ae540c69.mp3 Thu, 08 Apr 2010 13:00:00 -0400 TBA Paul McFadden http://streamer.perimeterinstitute.ca/mp3/eeb0f146-4051-4ecc-ad9f-c0632fd024fa.mp3 Science http://streamer.perimeterinstitute.ca/mp3/eeb0f146-4051-4ecc-ad9f-c0632fd024fa.mp3 Thu, 15 Apr 2010 13:00:00 -0400 Over the last decade there has been strong interest in the theory and phenomenology of particle propagation in quantum spacetime. The main results concern possible Planck-scale modifications of the "dispersion" relation between energy and momentum of a particle. I review results establishing that these modifications can be tested using observations of gamma rays from sources at cosmological distances. And I report recent progress in the understanding of the implications of spacetime expansion for such studies. I also discuss recent preliminary results suggesting that the same Planck-scale modifications of the dispersion relation might have an unexpected role in gravitational collapse. Giovanni Amelino-Camelia http://streamer.perimeterinstitute.ca/mp3/2da6eea2-c9ca-4ddc-b68a-919a52fecb3b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/2da6eea2-c9ca-4ddc-b68a-919a52fecb3b.mp3 Thu, 30 Sep 2010 13:00:00 -0400 A remarkable result from heavy ion collisions at the Relativistic Heavy Ion Collider is that shortly after a collision, the medium produced behaves as a nearly ideal liquid. The system is very dynamic and evolves from a state of two colliding nuclei to a liquid in a time roughly equivalent to the time it takes light to cross a proton. Understanding the mechanisms behind the rapid approach to a liquid state is a challenging task. In recent years holography has emerged as a powerful tool to study non-equilibrium phenomena, mapping the (challenging) dynamics of quantum systems onto the dynamics of classical gravitational systems. The creation of a liquid in a quantum theory maps onto the classical process of gravitational collapse and black hole formation. I will describe how one can use holography to study processes which mimic the dynamics of heavy ion collisions. Paul Chesler http://streamer.perimeterinstitute.ca/mp3/5a4b5ba7-a5cb-4b2b-9111-286679c6e0e9.mp3 Science http://streamer.perimeterinstitute.ca/mp3/5a4b5ba7-a5cb-4b2b-9111-286679c6e0e9.mp3 Thu, 07 Oct 2010 13:00:00 -0400 I discuss a model for particle acceleration in the current sheet separating the open and closed field line regions, and crossing the neutral line region, of a pulsar's magnetosphere, which has substantial kinship to the phenomena observed in planetary magnetospheres within the solar system. Possible applications to gamma ray emission from pulsars are also described. Jonathan Arons http://streamer.perimeterinstitute.ca/mp3/56ba41be-4657-4961-96f2-67dee7c1eb98.mp3 Science http://streamer.perimeterinstitute.ca/mp3/56ba41be-4657-4961-96f2-67dee7c1eb98.mp3 Thu, 14 Oct 2010 13:00:00 -0400 I will present the latest results from the searches for gravitational waves from the coalescence of binary systems of neutron stars and black holes in LIGO and Virgo data. We present results on data from the Fifth Science Run LIGO run S5 from Nov 2005 to Oct 2007, which was joint with Virgo's first Science Run VSR1 from May to Oct 2007. We also show how these methods are being applied in the current LIGO S6/ Virgo VSR2 data-taking run started in July 2009, and recently ended in October 2010. Gabriela Gonzalez http://streamer.perimeterinstitute.ca/mp3/777600a7-f7be-4338-82d3-f046fbc20c41.mp3 Science http://streamer.perimeterinstitute.ca/mp3/777600a7-f7be-4338-82d3-f046fbc20c41.mp3 Thu, 28 Oct 2010 13:00:00 -0400 Numerical simulations of binary black holes with spin have revealed some surprising behavior: for antialigned spins in the orbital plane, 1) one sees an up-and-down "bobbing" of the entire orbital plane at the orbital frequency and 2) the merged black hole receives an enormous kick that depends on the phase at merger. Natural questions are: What causes the bobbing? Can the kick be viewed as a post-merger continuation of the bobbing? We show that this type of bobbing is in fact ubiquitous in relativistic mechanics, occurring independently of the type of force holding two spinning bodies in orbit. The cause can be identified as a spin correction to the naive center of mass of a body; the effect is analogous to Thomas precession and is ``purely kinematical'' in the same way. Since a kick requires the release of field momentum, it is instead very dependent on the type of force holding bodies in orbit. In a mechanical analog (spinning balls connected by a string), there is bobbing but can be no kick. In an electromagnetic analog, one should be able to tune the kick independently of the bobbing. In the gravitational case the spin parameter happens to control both bobbing and kick, making separate tuning impossible and giving the appearance of causation to two essentially unrelated phenomena. Our answers are therefore: the bobbing is caused by a purely kinematical effect of spin, and the kick cannot be viewed its post-merger continuation. Sam Gralla http://streamer.perimeterinstitute.ca/mp3/5c8c953d-b086-4fbc-845e-da14876dfe38.mp3 Science http://streamer.perimeterinstitute.ca/mp3/5c8c953d-b086-4fbc-845e-da14876dfe38.mp3 Thu, 11 Nov 2010 13:00:00 -0500 There has been a growing interest in electromagnetic counterparts to gravitational wave signals. Of particular interest here, are counterparts to gravitational wave signals from super-massive black hole mergers. We consider a circumbinary disk, hollowed out by torques from the binary, and provide an analytic solution to its response following merger. There are two changes to the potential which occur during the merger process: an axisymmetric mass-energy loss and asymmetric recoil kick given to the resulting super-massive black hole. With a brief literature search we argue that, for fiducial disk values and for black hole spins aligned and anti-aligned with the orbital angular momentum, throughout the majority of parameter space the mass loss well dominates the effects of the recoil kicks on the circumbinary disk. This, along with assuming vertical hydrodynamic equilibrium, reduces the problem to one dimension. Using a 1D hydrodynamical code we explore the majority of parameter space and describe the different possible flows. In the 1D case, we give analytic approximations for the locations of the first shocks, their strengths, and the final density after the disk has again reached a steady state. This allows one to determine the temperature jump across the shock front and determine the observability, modulo the yet unknown disk mass. Nate Bode http://streamer.perimeterinstitute.ca/mp3/0281068f-1e49-4c64-be2f-bb2b410cf7a5.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0281068f-1e49-4c64-be2f-bb2b410cf7a5.mp3 Thu, 02 Dec 2010 15:00:00 -0500 NANOGrav is a consortium of radio astronomers and gravitational wave physicists whose goal is to detect gravitational waves using an array of millisecond pulsars as clocks. Whereas interferometric gravitational wave experiments use lasers to create the long arms of the detector, NANOGrav uses earth-pulsar pairs. The limits that pulsar timing places on the energy density of gravitational waves in the universe are on the brink of limiting models of galaxy formation and have already placed limits on the tension of cosmic strings. Pulsar timing has traditionally focused on stochastic sources, but most recently I have been investigating the idea of detecting individual gravitational wave bursts wherein there are some interesting advantages. I will also demonstrate how the array can be used to reconstruct the waveform and obtain its direction. Andrea Lommen http://streamer.perimeterinstitute.ca/mp3/6ea15879-95b3-4ec5-afc8-016e2b0cfce6.mp3 Science http://streamer.perimeterinstitute.ca/mp3/6ea15879-95b3-4ec5-afc8-016e2b0cfce6.mp3 Thu, 16 Dec 2010 15:00:00 -0500 Inflation is one of the foundational paradigms of our picture of the Universe. Yet distinguishing between the multitude of different inflationary models presents major observational challenges. In this talk, I will discuss a number of inflationary observables, specifically the tilt and running of the primordial power spectrum, compensated isocurvature modes, and non-Gaussianity, and the extent to which they might be constrained by future galaxy surveys and 21 cm experiments. Jonathan Pritchard http://streamer.perimeterinstitute.ca/mp3/03126e21-4bb7-4c13-8896-7a8b49c4c213.mp3 Science http://streamer.perimeterinstitute.ca/mp3/03126e21-4bb7-4c13-8896-7a8b49c4c213.mp3 Thu, 06 Jan 2011 13:00:00 -0500 The long awaited discovery of the double radio pulsar system, PSR J0737-3039A/B, surpassed most expectations, both theoretical and observational, as a tool to probe general relativity, stellar evolution and pulsar theories. The Double Pulsar provides a unique and the most complete and clean test of theories of gravity in a regime sensitive to possible strong-gravitational self-field effects. All six post-Keplerian parameters have been measured (including the measurement of the relativistic spin precession), some parameters to a precision of 10^{-4}. Maxim Lyutikov http://streamer.perimeterinstitute.ca/mp3/9ae2ba39-ea1b-444d-af6f-84714f685d6d.mp3 Science http://streamer.perimeterinstitute.ca/mp3/9ae2ba39-ea1b-444d-af6f-84714f685d6d.mp3 Fri, 04 Feb 2011 13:00:00 -0500 Assuming exotic matter, several models representing static, spherically symmetric wormhole solutions of Einstein's field equations have been considered in the literature. We examine the dynamical stability of such wormholes in one of the simplest model, in which the matter is described by a massless ghost scalar field, and prove that all solutions are unstable with respect to linear fluctuations and possess precisely one unstable, exponentially in time growing mode. Numerical simulations of the nonlinear field equations suggest that these wormholes either expand or collapse and form a black hole. The stability problem for alternative models including electrically charged wormholes is also discussed. Olivier Sarbach http://streamer.perimeterinstitute.ca/mp3/8eb81bc7-739f-41a7-9e24-cecbc9e069e9.mp3 Science http://streamer.perimeterinstitute.ca/mp3/8eb81bc7-739f-41a7-9e24-cecbc9e069e9.mp3 Thu, 17 Feb 2011 13:00:00 -0500 The upcoming launch of the space-based gravitational wave interferometer detector LISA will yield an unprecedented amount of astrophysical and cosmological science from a variety of gravitational wave sources. Among these, the extreme mass ratio inspirals (EMRIs) of stellar-mass compact objects into supermassive black holes will provide a unique opportunity to test the predictions of General Relativity for strongly gravitating systems since the masses and spins of these sources are expected to be measured with precisions better than about 1 part in 10^4. Such highly precise measurements require modeling the dynamics of EMRIs and their gravitational waves with high accuracy. In this talk, I discuss using methods of effective field theory (EFT) to accomplish this. Since EMRIs lose energy to gravitational waves, I introduce an open systems framework that proves to be a necessary ingredient to correctly describe EMRIs within the EFT formalism. I will discuss my recent derivation of the equations of motion and waveforms through third order in the mass ratio for a class of nonlinear scalar models that are analogous to the perturbative General Relativistic description of EMRIs. Time permitting, I will also discuss new results that are non-perturbative in the mass ratio in this model. Chad Galley http://streamer.perimeterinstitute.ca/mp3/53412f0d-9e1f-4ad7-aba5-60ea3d0e7a80.mp3 Science http://streamer.perimeterinstitute.ca/mp3/53412f0d-9e1f-4ad7-aba5-60ea3d0e7a80.mp3 Thu, 03 Mar 2011 13:00:00 -0500 The local and global properties of the retarded and Feynman Green functions to the wave equation in curved spacetime are crucial for radiation reaction in the classical theory and for renormalisation in the quantum quantum theory. Building on an insight due to Avramidi, we provide a system of transport equations for determining key fundamental geometrical bitensors determining the local Hadamard singularity structure of these Green’s functions. We illustrate their use in a semi-recursive approach showing how to determine covariant expansions to high order, for example, calculating the tail term reflecting backscattering by the curvature of spacetime to 20th order in the geodesic separation in a matter of minutes, and as the basis of numerical calculations. We also present an efficient method to construct covariant expansions of the tail term, without using the formal Hadamard light-cone expansion. Finally we discuss the relationship between the geodesic structure, quasi-normal modes with associated excitation factors and the global behaviour of Green functions in black hole space-times. Adrian Ottewill http://streamer.perimeterinstitute.ca/mp3/23de3cb1-6dc0-43ea-b9fd-3944aacd7b7f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/23de3cb1-6dc0-43ea-b9fd-3944aacd7b7f.mp3 Thu, 17 Mar 2011 13:00:00 -0400 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. Andreas Ross http://streamer.perimeterinstitute.ca/mp3/f0f8acdc-3043-40d3-a6e4-1ff28b86fe89.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f0f8acdc-3043-40d3-a6e4-1ff28b86fe89.mp3 Thu, 31 Mar 2011 13:00:00 -0400 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. We describe recent results on self-similar Lemaitre-Tolman-Bondi spacetime, indicating stability of scalar and odd parity perturbations, and instability of even parity perturbations. Brien Nolan http://streamer.perimeterinstitute.ca/mp3/fc69e4f4-d2d5-475a-9cd9-6bdfba65c1cc.mp3 Science http://streamer.perimeterinstitute.ca/mp3/fc69e4f4-d2d5-475a-9cd9-6bdfba65c1cc.mp3 Thu, 07 Apr 2011 13:00:00 -0400 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. I describe this cross-correlation method and potential applications to search LIGO and Virgo data for periodic GWs from systems with partially-known parameters, such as supernova remnants without an associated known pulsar, the center of the Milky Way Galaxy, and LMXBs John Whelan http://streamer.perimeterinstitute.ca/mp3/0dc6683e-0abe-4fb4-84c2-90053cabb4f5.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0dc6683e-0abe-4fb4-84c2-90053cabb4f5.mp3 Thu, 14 Apr 2011 13:00:00 -0400 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. Elizabeth Winstanley http://streamer.perimeterinstitute.ca/mp3/e82ffee7-bef6-4a1b-bbb9-4ca588719723.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e82ffee7-bef6-4a1b-bbb9-4ca588719723.mp3 Fri, 06 May 2011 10:00:00 -0400 TBA Viktor Toth http://streamer.perimeterinstitute.ca/mp3/a2cc528b-1d36-4a2e-af73-5f81b8b17477.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a2cc528b-1d36-4a2e-af73-5f81b8b17477.mp3 Thu, 26 May 2011 13:00:00 -0400 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. Cosimo Bambi http://streamer.perimeterinstitute.ca/mp3/b9deae60-6a31-4358-9279-ab1cfdfcd150.mp3 Science http://streamer.perimeterinstitute.ca/mp3/b9deae60-6a31-4358-9279-ab1cfdfcd150.mp3 Thu, 21 Jul 2011 13:00:00 -0400 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. Enrico Ramirez http://streamer.perimeterinstitute.ca/mp3/4346a086-fbbc-482b-8589-481993ac0299.mp3 Science http://streamer.perimeterinstitute.ca/mp3/4346a086-fbbc-482b-8589-481993ac0299.mp3 Thu, 28 Jul 2011 13:00:00 -0400 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. Neglecting the presence of the inhomogeneity can in fact introduce a systematic misinterpretation of cosmological data, leading to the distinction between an apparent and true value of the cosmological constant. We establish the theoretical framework to calculate the corrections to the apparent value of the cosmological constant by modeling the local inhomogeneity with a $Lambda LTB$ solution. Our assumption to be at the center of a spherically symmetric inhomogeneous matter distribution correspond to effectively calculate the monopole contribution of the non linear inhomogeneities surrounding us, which we expect to be the dominant one, because of other observations supporting a high level of isotropy of the Universe around us. By performing a local Taylor expansion we analyze the number of independent degrees of freedom which determine the local shape of the inhomogeneity, and consider the issue of central smoothness, showing how the same correction can correspond to different inhomogeneity profiles. Contrary to previous attempts to fit data using large void models our approach is quite general. The correction to the apparent value of the cosmological constant is in fact present for local inhomogeneity of any size, and should always be taken appropriately into account both theoretically and observationally. Antonio Enea Romano http://streamer2.perimeterinstitute.ca/mp3/11090133.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11090133.mp3 Thu, 29 Sep 2011 13:00:00 -0400 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. Richard O'Shaughnessy http://streamer2.perimeterinstitute.ca/mp3/11100049.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11100049.mp3 Thu, 06 Oct 2011 13:00:00 -0400 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. Numerical results for how Bowen-York parameters in the conformally flat initial value problem are related to the physical energy and momentum in systems with single and binary black holes will be presented. James Bardeen http://streamer2.perimeterinstitute.ca/mp3/11100089.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11100089.mp3 Thu, 13 Oct 2011 13:00:00 -0400 Bizon and Rostworowski have recently suggested that anti-de Sitter spacetime might be nonlinearly unstable to transfering energy to smaller and smaller scales and eventually forming a small black hole. We consider pure gravity with a negative cosmological constant and find strong support for this idea. While one can start with a single linearized mode and add higher order corrections to construct a nonlinear geon, this is not possible starting with a linear combination of two or more modes. One is forced to add higher frequency modes with growing amplitude. The implications of this turbulent instability for the dual field theory are discussed. Jorge Santos http://streamer2.perimeterinstitute.ca/mp3/11100053.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11100053.mp3 Thu, 20 Oct 2011 13:00:00 -0400 In inflationary theories, single field models are typically considered subject to slow-roll conditions. In this talk I will present current observational constraints on deviations from slow-roll, e.g. bounds coming from strong coupling considerations, scale-dependent non-Gaussianities and the tensor-to-scalar ratio. These constraints still allow significant violations of slow-roll conditions. Focusing on non-Gaussian signals, I will discuss a variety of intriguing observable signatures that can be found for fast-rolling single fields. Johannes Noller http://streamer2.perimeterinstitute.ca/mp3/11110070.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11110070.mp3 Thu, 10 Nov 2011 13:00:00 -0500 The development of virial mass estimates for the central black hole using one quasar spectrum has allowed a dramatic improvement in our understanding of supermassive black hole evolution. I will describe several new puzzles arising from the combination of virial masses with luminosity and redshift measurements, many of which are inconsistent with our current understanding of quasar evolution. I will also describe a new class of quasars that does not appear to fit easily into current models for quasar accretion. Charles Steinhardt http://streamer2.perimeterinstitute.ca/mp3/11110116.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11110116.mp3 Tue, 22 Nov 2011 14:00:00 -0500 Violation of unitarity in black hole evaporation has been puzzling physicist since the seminal work of Hawking in the seventies. Although there are hopes for a resolution of the problem in a full theory of quantum gravity, it has eluded us so far. Even less ambitious efforts considering only quantum corrections beyond the external field approximation have proven hard to attack in 4 dimensions. All these obstacles directed researchers to investigate the black hole evaporation problem in simpler 2-dimensional models. In this talk, we will present results on a new investigation of one of these models, the 2-dimensional Callan-Giddings-Harvey-Strominger (CGHS) model. Using a combination of analytical and high precision numerical tools, we are able to resolve CGHS black hole evaporation within the mean field approximation all the way to the point where the black hole area vanishes. Our results confirm some of the assumptions of the standard paradigm, and strongly suggest the recovery of unitarity within the full quantum theory. On the other hand, there are several surprising new results, in particular remarkable universal behavior in the evaporation of initially macroscopic black holes. This suggests that information about the collapsing matter that formed the black hole can not be recovered from the evaporation radiation. Though this separation of the questions of information loss and unitarity is peculiar to the 2-dimensional model, insights into the higher dimensional case can still be garnered. Details of the numerical methods used will also be discussed. Fethi Ramazanoglu http://streamer2.perimeterinstitute.ca/mp3/11120048.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11120048.mp3 Thu, 01 Dec 2011 13:00:00 -0500 After overviewing the fundamentals of magnetized relativistic jets production, I present the results of new global 3D general relativistic magnetohydrodynamic simulations of jet formation by black hole (BH) accretion systems. The simulations are designed to transport a large amount of magnetic flux to the center, more than the accreting gas can force into the BH. The excess magnetic flux remains outside the BH, impedes accretion, and leads to a magnetically arrested disc. We find powerful outflows. For a BH with spin parameter a = 0.5, the efficiency with which the accretion system generates outflowing energy in jets and winds is eta ~ 30%. For a = 0.99, we find eta ~ 140%, which means that more energy flows out of the BH than flows in. The only way this can happen is by extracting spin energy from the BH. Thus the a = 0.99 simulation represents an unambiguous demonstration, within an astrophysically plausible scenario, of the extraction of net energy from a spinning BH via the Penrose-Blandford-Znajek mechanism. Alex ander Tchekovskoy http://streamer2.perimeterinstitute.ca/mp3/11120028.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/11120028.mp3 Thu, 08 Dec 2011 13:00:00 -0500 The observational search for non-Gaussian statistics in the initial conditions of the universe is a powerful, Kendrick Smith http://streamer2.perimeterinstitute.ca/mp3/12010127.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/12010127.mp3 Wed, 18 Jan 2012 12:45:00 -0500 Cosmological N-body simulations are now being performed using Newtonian gravity on scales larger than the Hubble radius. It is well known that a uniformly expanding, homogeneous ball of dust in Newtonian gravity satisfies the same equations as arise in relativistic FLRW cosmology, and it also is known that a correspondence between Newtonian and relativistic dust cosmologies continues to hold in linearized perturbation theory in the marginally bound/spatially flat case. Nevertheless, it is far from obvious that Newtonian gravity can provide a good global description of an inhomogeneous cosmology when there is significant nonlinear dynamical behavior at small scales. We investigate this issue in the light of a perturbative framework that we have recently developed, which allows for such nonlinearity at small scales. We propose a relatively straightforward "dictionary"---which is exact at the linearized level---that maps Newtonian dust cosmologies into general relativistic dust cosmologies, and we use our "ordering scheme" to determine the degree to which the resulting metric and matter distribution solve Einstein's equation. We find that Einstein's equation fails to hold at "order 1" at small scales and at "order $epsilon$" at large scales. We then find the additional corrections to the metric and matter distribution needed to satisfy Einstein's equation to these orders. While these corrections are of some interest in their own right, our main purpose in calculating them is that their smallness should provide a criterion for the validity of the original dictionary (as well as simplified versions of this dictionary). We expect that, in realistic Newtonian cosmologies, these additional corrections will be very small; if so, this should provide strong justification for the use of Newtonian simulations to describe relativistic cosmologies, even on scales larger than the Hubble radius. Stephen Green http://streamer2.perimeterinstitute.ca/mp3/12020128.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/12020128.mp3 Thu, 09 Feb 2012 13:00:00 -0500 I review the uses of effective field theory (EFT) techniques, originally developed in particle physics, to study gravitational dynamics. I will focus on the EFT approach to gravitational wave (GW) radiation, aka NRGR, and show how it has succeeded in producing the most accurate description of spinning binary systems to date, opening the door to a new era of precise astrophysical & cosmological measurements and tests of General Relativity via GW interferometry. I will also briefly discuss EFT applications for black hole dissipation/absorption, inflationary dynamics and  high energy gravitational scattering. Rafael Porto http://streamer2.perimeterinstitute.ca/mp3/12030088.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/12030088.mp3 Thu, 01 Mar 2012 13:00:00 -0500 In this talk I will present evidence that accounting for the presence of hierarchies in string compactifications naturally leads to a UV sensitivity of dark matter in contrast to what is usually assumed. In particular, we will see that the existence of cosmological moduli may lead to a non-thermal history for the early universe and modifications in the primordial production of dark matter. If such a history were realized it would not only require probing new regions in dark matter searches, but also imply that a detection of dark matter would provide a direct probe on the early universe and the UV -- contrary to the thermal WIMP case. Regardless of the history of the early universe I will argue that if current string constructions are representative of more general models then all weak-scale dark matter would indeed be UV sensitive and would be a new prediction of string theory - falsifiable by experiment. Thomas Sotiriou http://streamer2.perimeterinstitute.ca/mp3/12030085.mp3 Science http://streamer2.perimeterinstitute.ca/mp3/12030085.mp3 Thu, 22 Mar 2012 13:00:00 -0400