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GRAVITY THEORY SEMINARS SPRING 2011
The seminars take place every Wednesday at 3:15 pm in Room 4102 unless
otherwise stated below. For more information about GRT group seminars contact Manuel Tiglio (Physics 4205E and CSIC 4129).
For information concerning the Elementary
Particle Theory group seminars see the EPT seminar page, the Theoretical Quarks, Hadrons, Nuclei
group seminars see the TQHN seminar page,
and scheduled seminars in the UMD Physics Department see the Department seminar pages.
Seminars from previous semesters can be found here: spring 2002, fall 2002, spring 2003, fall 2003, spring 2004, fall 2004, spring 2005, fall 2005, spring 2006, fall 2006, spring 2007, fall 2007, spring 2008, fall 2008, spring 2009, fall 2009, 2010.
DATE, TIME, PLACE 
SPEAKER, AFFILIATION, TITLE 
MCFP Colloquium 
Neal Weiner, New York University 
Wednesday, Feb. 2 
Aron
Wall, University of Maryland Title:
A Quantum Singularity Theorem Abstract:
In classical general relativity, the Penrose singularity theorem tells us
that black holes must have singularities inside of them. However, the
result does not apply to quantum spacetimes, which can have negative energy
densities. I will describe how the generalized second law (GSL) can be
used to prove a singularity theorem even for quantum black holes. Depending
on the interests of the audience, I may also discuss how the GSL applies to
the big bang singularity, baby universes, traversable wormholes, warp drives,
time machines, and negative mass objects. This is intended to be an informal, interactive blackboard talk explaining arXiv:1010.5513. 
JSI Seminar 
Jonathan
McKinney, Stanford University Title:
Observing Black Holes Abstract:
Black hole accretion systems are among the most powerful phenomena in the
Universe and are excellent laboratories for probing and testing general
relativity. I discuss how such systems work, and I show how black hole spins
can be measured using photon spectra from black hole xray binaries. Such
measurements are then shown to be reliable by using threedimensional general
relativistic magnetohydrodynamical simulations. I also use black hole
accretion simulations to reveal how relativistic jets are launched and remain
stable despite wellknown magnetic kink instabilities. Such jet simulations
show how observations of jets from active galactic nuclei implicate the
cosmological evolution of black hole spin. 
MCFP Colloquium 
Neal Weiner, New York University 
JSI Seminar 
Neal
Dalal, CITA, University of Toronto 
JSI Seminar 
Stefano
Profumo, University of California, Santa Cruz Abstract:
New physics at the electroweak scale might unlock the mysteries of the
generation of the (baryonic) matterantimatter asymmetry and of the particle
nature of dark matter. I will review recent progress on understanding
baryogenesis at the electroweak phase transition, and the multitude of
experimental tests that this scenario offers, including collider, gravity
waves and electric dipole moment searches. I will argue that this scenario is
firmly falsifiable, with a timeline of only a few years. I will then discuss
searches for weakscale particle dark matter in astrophysical data, including
an updated review of controversial signals in cosmicray and gammaray data.
I will address the question of whether it is feasible to learn about New
Physics "from the Sky", and outline theoretical and observational
strategies for a roadmap towards the discovery of the nature of dark matter. 
JSI Minisymposium 
“Millisecond
Pulsars” Talks: Overview
of millisecond pulsars  Alice Harding Observations
of accreting Xray MSPs  Tod Strohmayer Using
millisecond pulsars to detect 10^{9} to 10^{7} Hz gravitational waves (and
why we care)  Cole Miller MSPs
masquerading as something more interesting  Kevork Abazajian The MSP future with NICER  Zavan Arzoumanian 
JSI Seminar 
Avery Broderick (CITA, University of Toronto) Abstract:
The Event Horizon Telescope, an Earthsized array of mm and submm
telescopes, provides the novel ability to probe a handful of nearby
supermassive black holes on subhorizon spatial scales. Already this has
provided the best evidence to date for the existence of an event horizon and
begun to probe the nature of the accretion flow onto the black hole at the
center of the Milky Way. In the near future, similar observations of the supermassive
black hole at the center of M87 will begin to reveal how ultrarelativistic
jets are formed. I will describe how these observations are performed, what
we have learned already, and how we will use future observations to constrain
the gastrophysics and environment of black holes, and even the nature of
gravity within their vicinity. 
JSI Seminar 
Louis
Strigari (Stanford University) 
Spring Break (March 2027) 

MCFP Colloquium 
Michael Levin, University
of Maryland Topological
order and quantum entanglement Abstract: Topological
quantum field theories (TQFTs) were first discovered in the 1980s in the
context of string theory. Surprisingly, TQFTs also describe the low energy
physics of certain quantum condensed matter systems. These systems are said
to contain "topological order." But what exactly is topological
order? In my talk, I will show that topological order is fundamentally a kind
of nonlocal quantum entanglement in the
ground state wave function. I will introduce a quantity  called
"topological entropy"  that measures precisely this nonlocal
entanglement. 
Ph D dissertation defense 
Aron Wall, University of Maryland. 
Wednesday, April 6 
Jonah Kanner (University of Maryland) Honey,
LIGO's on the phone! Abstract: During
2009 and 2010, the kilometer scale interferometers known as LIGO and Virgo
simultaneously observed the skies for transient gravitational
wave signals. Nearly realtime software analyzed data from this global network to estimate
the source positions of gravitational wave triggers with only a few minutes
of latency. To search for potential optical afterglows of candidate
gravitational wave sources, an oncall team of experts inspected each
gravitational wave trigger to decide if robotic telescopes should be used to
observe the estimated source position of the candidate. This
talk will discuss the motivation and methodology of the search,the ability of
gravitational wave detectors to localize events on the
sky, and the joys and challenges of working with an experiment that sometimes
calls in the middle of the night. 
JSI MiniSymposium 
“Emerging from the Dark Ages” Talks: The First
Stars and Galaxies from Redshift 20 to Reionization – Massimo Stiavelli Coming into
the Light: Galaxy Clusters and the End of Cosmic Structure Formation – Adam
Mantz Formation
and Likely EM and GW Signatures of the First Black Holes – Peter Shawhan Learning About
the Dim Ages Using Fossil Galaxies – Massimo Ricotti Expected
Information from Future Instruments – Jeremy Schnittman

Wednesday, April 13 
Enrico Barausse,
University of Maryland Title:
Test bodies and naked singularities: is the selfforce the cosmic censor? Abstract:
Jacobson and Sotiriou showed that rotating black holes could be spunup past
the extremal limit by the capture of nonspinning test bodies, if one
neglects radiative and selfforce effects. This would represent a violation
of the Cosmic Censorship Conjecture in fourdimensional, asymptotically flat
spacetimes. We show that for some of the trajectories giving rise to naked
singularities, radiative effects can be neglected. However, for these orbits
the conservative selfforce is important, and seems to have the right sign to
prevent the formation of naked singularities. 
Ph D dissertation defense 
Darian Boggs, University of Maryland and NASA Goddard. 
Wednesday, April 20 
Sarah Caudill, Louisiana State University Title: Status of the Search for Gravitational Wave Ringdowns from
Perturbed Black Holes Abstract: I will report on the status of the search for gravitational
wave ringdowns from perturbed black holes with masses between 25100 M_sun in
LIGO's fifth science run. This mass range is the first regime explored as
part of the ringdown search's participation in the InspiralMergerRingdown
(IMR) project, a joint effort between LIGO's Burst group and Compact Binary
Coalescence group to study the efficiency with which we will detect high mass
binary black holes with masses between 25500 M_sun. I will also review the
recent changes made to the ringdown analysis pipeline for LIGO's fifth
science run. These changes include the implementation of a new 3D coincidence
test to compute the distance between pipeline triggers in frequency, quality,
and time space as well as a number of improvements to increase efficiency and
automation in the pipeline. 
MCFP Colloquium 
Matias Zaldarriaga, Institute for Advanced
Study, Princeton. Abstract: We now know that the seeds necessary to form
structure in our Universe were in place at the start of the hot big bang
phase of our Universe. Thus detailed measurements of the statistical
properties of these seeds might shed light on what came before the hot big
bang. I will discuss the current state of the subject and recent theoretical
results on how best to describe the properties of the initial seeds and what
different measurements can teach us about what produced those seeds. 
Wednesday, May 4 
Cole Miller, University of Maryland
Abstract: Stellar mass (~few to tens of solar masses) and
supermassive (millions to billions of solar masses) black holes are well
established, but there is still doubt about ones of intermediate mass
(hundreds to thousands of solar masses). If intermediatemass black
holes do exist, they have many implications as unique gravitational wave
sources, with ties to many frontier topics in astrophysics including the
first stars, the dynamics of dense stellar clusters, and the formation and
evolution of supermassive black holes. After giving a brief overview of
the evidence that they exist and proposed scenarios for their birth and
growth, I will focus most of my talk on the binaries they likely form and
their potential, as gravitational radiation sources, to provide remarkably
precise tests of the predictions of general relativity in strong gravity. 
Wednesday, May 11 
Luc Blanchet, Institut d’Astrophysique de Paris Title: Does an atom interferometer test the gravitational
redshift? Abstract: In a recent paper, H. Mueller, A. Peters and S.
Chu claimed that atom interferometry experiments provide a very accurate test
of the gravitational redshift (or Einstein effect). In this seminar we
analyze this claim in the framework of general relativity and of different
alternative theories. We show that the phase difference of the matter wave
between the two paths of the interferometer is zero in most theoretical
frameworks used to interpret the equivalence principle. We thus conclude that
atom interferometers do not test the redshift. We also show that frameworks
which would permit this test pose serious problems such as the violation of
fundamental principles of quantum mechanics.

JSI Seminar 
Ilya Mandel, MIT Title: GW astrophysics with compact binaries Abstract: The groundbased gravitationalwave
telescopes LIGO and Virgo approach the era of first detections. In this
talk, I will review the current knowledge of the coalescence rates and
parameter distributions of merging neutronstar and blackhole binaries. I
emphasize the bidirectional connection between gravitationalwave astronomy
and conventional astrophysics. Astrophysical input will make possible
informed decisions about optimal detector configurations and search
techniques. Meanwhile, rate upper limits, detected merger rates, and the
distribution of masses and spins measured by gravitationalwave searches will
constrain astrophysical parameters through comparisons with astrophysical
models. I report on ongoing efforts to develop a framework for converting
gravitationalwave observations into improved constraints on astrophysical
parameters and discuss future developments necessary to the success of
gravitationalwave astronomy. 
Wednesday, May 18 
Jennifer
Seiler, Goddard Space Flight Center, NASA. Abstract:
I will present an analysis of the properties of binary black hole inspirals
obtainable from the spherical harmonic modes of the emitted gravitational
waveforms. Using wellknow methods we extract the final spins, kicks, and
mass of the merged black holes. By the energy loss from
the waves we can estimate the rate of inspiral, and from the asymmetric
spherical harmonic modes we can obtain the orbital frequency. Then,
using Wigner rotation to find the angles that minimize the asymmetric
spherical harmonic modes we can obtain the angles of the precession
of the system. Effectively we are finding rotation angles that would make the
line from the observer to the system always line up with
the orbital angular momentum. Thus we show that most of the astrophysical
qualities and dynamics from precessing binary black hole systems can be reconstructed from observed waveforms. 


Send comments to: tiglio AT umd.edu