GR Seminars Spring 2013

The standard seminar time and place is Wednesday, 1:30pm, Room 4102. Fall 2013 Seminars coming soon.
Non-standard times and/or places are indicated in red type.

DATE	SPEAKER	AFFILIATION	TITLE
Jan. 23	Jonathan McKinney	UMD	Black Hole Event Horizon Phenomena: Observations Confront Theory
Jan. 30	Donghui Jeong	Johns Hopkins	New Ways of Searching for the Primordial Gravitational Wave from Large Scale Structure
Feb. 6	Jeremy Schnittman	NASA Goddard	Finding Stellar-Mass Black Holes with Gravitational Lensing
Feb. 13	Francois Foucart	CITA	The Outcome of Black Hole-Neutron Star Mergers: Predictions from Numerical Relativity
Feb. 20	Rob Owen	Oberlin	Spacetime Vorticity, Tendicity, and the Near-Field Structure of Dynamical Black Holes
Feb. 27 (2pm,1201) MCFP Colloquium	James Lattimer	Stonybrook	A Convergence on an Understanding of the Dense Matter Equation of State
Mar. 6	Lam Hui	Columbia	Testing Gravity with Pulsars, Black Holes and the CMB CANCELLED
Mar. 13	Scott Field	UMD	Fast Evaluation of Asymptotic Waveforms from Gravitational Perturbations
Mar. 27	B. Sathyaprakash	Cardiff	Shedding Light on Black Holes
Apr. 3	Sam Gralla	UMD	Thermodynamics of a Black Hole with Moon
Apr. 10 (2pm,1201) MCFP Colloquium	Dam Son	Chicago	Newton-Cartan Geometry and the Effective Field Theory of the Quantum Hall States
Apr. 17	Claudia de Rham	Case Western	Pulsar Tests of Modified Gravity
Apr. 18 (3:30pm) Joint with EPT	Ira Rothstein	Carnegie Mellon	Generating Solutions to Einsteins Equations from the Yang-Mills Action
Apr. 24			NO SEMINAR
May 1	Lam Hui	Columbia	Testing Gravity with Pulsars, Black Holes and the CMB
May 8	Frans Pretorius	Princeton	Eccentric Compact Object Mergers

For more information about GRT group seminars contact Sam Gralla or Alexandre Le Tiec. 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 calendar. The webpages of the UMD-NASA Goddard Joint Space-Science Institute
and the Maryland Center for Fundamental Physics also hold regular events of interest to the group.

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, spring 2011, fall 2011, fall 2012.


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ABSTRACTS
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Jonathan McKinney, UMD
Black Hole Event Horizon Phenomena: Observations Confront Theory

The black holes in M87 and SgrA* have event horizons with the largest
angular size on the sky among all black holes in the Universe. Such
event horizon scales are now accessible to Earth-wide radio arrays,
so these systems potentially offer the best chance to probe and even
test Einstein's general relativity theory. I discuss the latest observations,
rough interpretations, theories, and simulations that attempt to make
sense of what goes on near black hole event horizons.

===============================================

Donghui Jeong, Johns Hopkins
New Ways of Searching for the Primordial Gravitational Wave from
Large Scale Structure

Primordial gravitational wave (PGW) is a valuable probe of the physics
of the early universe as the amplitude of it is directly related to the energy
scale of inflation. Most popular method of detecting PGW is using a parity
odd (B-mode) polarization pattern of the cosmic microwave background
radiation. Then, do we have any signature from the large scale structure?

In this talk, we shall discuss two possible ways that PGW affect the large
scale structure: 1) through light deflection and 2) through intrinsic
correlation. We shall show that one can probe these two effects from the
B-mode of weak gravitational lensing and the off-diagonal correlation of
galaxies. For both cases, the intrinsic correlation dominates over the light
deflection in standard cosmologies as PGW amplitude decays once the
mode comes inside of the horizon.

reference:
Jeong & Kamionkowski [arXiv:1203.0302]
Schmidt & Jeong [arXiv:1204.3625]
Jeong & Schmidt [arXiv:1205.1512]
Schmidt & Jeong [arXiv:1205.1514]

===============================================

Jeremy Schnittman, NASA Goddard
Finding Stellar-Mass Black Holes with Gravitational Lensing

Over the past two decades, ground-based optical surveys of millions of
stars in the galactic bulge have produced thousands of microlensing
events. Due to a fundamental mass-distance-velocity degeneracy in
the microlensing light curve, it has been very difficult to determine
accurate lens masses for most of these events. Here we discuss two
promising techniques for breaking this degeneracy: high-precision
astrometry, and additional timing features present in binary
systems. We show that the current observational data is of sufficient
quality to detect the first known binary black holes. With these
detections, we will be able to learn important information about the
evolution of massive stars and binary systems.

===============================================

Francois Foucart, CITA
The Outcome of Black Hole-Neutron Star Mergers: Predictions from
Numerical Relativity

The gravitational wave signal emitted by the merger of a black hole and
a neutron star will be observable by the next generation of gravitational
wave detectors. Such mergers can also be accompanied by detectable
electromagnetic signals: short gamma-ray bursts and their afterglow,
optical transients from the radioactive decay of neutron-rich material
ejected during merger, and radio emission as that ejecta decelerates in
the interstellar medium. The existence of these counterparts and the
characteristics of the gravitational wave signal are however sensitive
to the parameters of the binary (masses, spins, eccentricity), and to the
unknown equation of state of the neutron star material. In this talk, I will
discuss what numerical simulations have told us about the outcome of
black hole-neutron star mergers, and about their gravitational wave
emission. I will focus in particular on the few general relativistic
simulations performed in the range of black hole masses currently favored
by both population synthesis models and the observation of stellar mass
black holes, and on their strong differences with respect to previous
results obtained for lower black hole masses.

===============================================

Rob Owen, Oberlin
Spacetime Vorticity, Tendicity, and the Near-Field Structure of
Dynamical Black Holes

Numerical relativity is an invaluable tool for exploring the strongly
nonlinear dynamics of curved spacetime. However one of the first
steps in numerical simulation -- fixing a coordinate system in which
to express the partial differential equations -- breaks the fundamental
physical symmetry of the true problem. A good intuitive understanding
of black hole collisions would require tools that reduce, or at least
clarify, the effects of their own inherent coordinate ambiguity. I will
report one such effort that I've been pursuing along with a number of
colleagues, involving the stretching and twisting of fleets of inertial
observers, and will also comment on the relationship between this
formalism and some (more mainstream) constructions that define
quasilocal quantities such as black-hole spin and multipole moments.

===============================================

James Lattimer, Stonybrook
A Convergence on an Understanding of the Dense Matter Equation
of State

Determining the equation of state of neutron star matter has been a
long-sought goal. Recently, there has been a remarkable convergence
in our understanding of dense matter from several directions: multiple
nuclear experiments, theoretical neutron matter studies, pulsar mass
determinations, and estimates of neutron star masses and radii from
X-ray sources. The key parameters are related to the symmetry energy
of matter near the nuclear saturation density, which is closely related
to the neutron star mass-radius relation. Observations indicate that
the maximum neutron star mass is in excess of 2 solar masses, and,
together with nuclear experimental and theoretical studies, restrict
the radii of neutron stars with approximately 1.4 - 1.5 solar masses to
lie in the range 11 to 12.5 km. In addition, the rapid cooling recently
found for the neutron star in the Cassiopeia supernova remnant indicates
that both neutron superfluidity and proton superconductivity exist in its
interior, and tightly constrain their respective critical temperatures.

===============================================

Lam Hui, Columbia
Testing Gravity with Pulsars, Black Holes and the CMB

We will discuss three different topics all connected with the nature
of gravity: 1. a way to measure gravitational waves using scattering
with binary systems; 2. a way to test generic scalar-tensor theories by
looking for off-centered supermassive black holes; 3. a way to probe
fluctuations on superhorizon scales using the microwave background.

===============================================

Scott Field, UMD
Fast Evaluation of Asymptotic Waveforms from Gravitational
Perturbations

In the context of blackhole perturbation theory, I describe evaluation
of an asymptotic waveform from data (Regge-Wheeler-Zerilli master
functions given as a time-series) recorded at a fixed radial location.
The asymptotic waveform is represented as a convolution of the data
with a time-domain kernel comprised of a few damped exponentials.
In turn, each exponentials' strength and damping rate arises from a
sum-of-poles approximation of a Laplace frequency domain kernel.
I will motivate the origin of the frequency domain kernel as well as
the numerical techniques needed for its sum-of-poles approximation.
The method is used to study late-time decay tails at null-infinity,
"teleportation" of a signal between two finite radial values, and
luminosities from extreme-mass-ratio binaries. Through numerical
simulations with data recorded as close as r = 30M, I compute
asymptotic waveforms with late-time -4 decay (for l = 2 perturbations),
and also luminosities from circular and eccentric orbits that match
frequency domain results to relative errors of better than 10^{-9}.
These results are achieved without a compactification scheme,
extrapolation procedure or solving a PDE.

===============================================

B. Sathyaprakash, Cardiff
Shedding Light on Black Holes

Observation of black holes in the gravitational window will impact
many areas in astrophysics, cosmology and fundamental physics: Black
hole mass functions and their spins could tell us about astrophysics
of their formation and evolution; their redshift distribution and
demographics might reveal the origin of galaxies and if seed black
holes were small or large; accurate measurement of distances to black
hole coalescences could be useful for cosmography; accurate phasing of
the signals could help test general relativity and explore black hole
spacetimes. In this talk I will discuss the prospects for deploying
black holes for observational astronomy and cosmology as well as what
we could learn about black holes from gravitational wave observations.

===============================================

Sam Gralla, UMD
Thermodynamics of a Black Hole with Moon

Much of black hole thermodynamics is limited to systems with a high
degree of symmetry. In this talk I will discuss a non-stationary, non-
axisymmetric black hole spacetime that nevertheless admits a standard
thermodynamics: a black hole corotating with an orbiting moon. More
precisely, we consider a Kerr black hole perturbed by a particle on the
circular orbit whose frequency matches that of the event horizon. The
key point is that the spacetime has a "helical" Killing vector that generates
the event horizon, allowing the surface gravity to be defined in the
standard way. The surface gravity is uniform on the horizon and should
correspond to the Hawking temperature of the black hole. We calculate
the change in surface gravity/temperature, finding it negative: the moon
has a cooling effect on the black hole. We also calculate the area/entropy
of the perturbed black hole, finding no change from the background Kerr
value. Generalizations to alternative theories, higher dimensions, and
alternative asymptotics (e.g., ads) should be possible, allowing one to
probe the behavior of an interacting black hole in a variety of settings.
This work is in collaboration with Alexandre Le Tiec.

===============================================

Dam Son, Chicago
Newton-Cartan Geometry and the Effective Field Theory of the
Quantum Hall States

A nonrelativistic system in an external metric exhibits a gauge version
of Galilean invariance. This symmetry put constraints on the effective
field theory of quantum Hall states. We describe how the effective field
theory satisfying these constraints can be constructed using the formalism
of the Newton-Cartan geometry. Physical consequences for electromagnetic
response at nonzero wavenumbers are derived.

===============================================

Claudia de Rham, Case Western
Pulsar Tests of Modified Gravity

Modifications of Gravity usually come hand in hand with new polarizations
that can be probed on astrophysical and cosmological scales. In specific
models such as Massive Gravity, the force mediated by these extra
polarizations are screened via the Vainshtein mechanism. After reviewing
the theoretical framework behind this mechanism, I will show how it
affects the gravitational radiation emitted by binary pulsar systems.
In the simplest model, the mechanism successfully screens the effect
from scalar fields conformally coupled to matter, although gravitational
radiation is less suppressed relative to its general relativity predictions
than static fifth forces effects within pulsar systems. I will then discuss
extension of the mechanism to more general Galileon theories.

===============================================

Ira Rothstein, Carnegie Mellon
Generating Solutions to Einsteins Equations from the Yang-Mills Action

In this talk I will show how to generate solutions to Einsteins equations
without any reference to the Einstein-Hilbert action starting from the
Yang-Mills action by utilizing on-shell unitarity techniques in conjunction
with BCFW (Britto, Cachazo, Feng, Witten) recursion relations.

===============================================

Frans Pretorius, Princeton
Eccentric Compact Object Mergers

Binary compact object mergers are among the primary gravitational wave
sources expected to be observed by the next generation of ground-based
gravitational wave detectors. Mergers where one or both compact objects
are neutron stars will further produce electromagnetic emission, and
coincident observation of this together with gravitational wave emission
could teach us much about the progenitor systems, test general relativity
in the dynamical strong field regime, and help elucidate the nature of
matter at nuclear density. I will discuss some ongoing work modeling
such mergers within the context of general relativity coupled to ideal
hydrodynamics, focusing on black hole-neutron star and binary neutron
systems merging with sizeable eccentricity. Large eccentricity is expected
for mergers that occur following dynamical capture in dense cluster
environments, and though they may be rarer than the traditional quasi-
circular inspiral, they could exhibit strikingly different behavior, including
zoom-whirl orbital dynamics and large amounts of unbound material for
cases where the neutron star is tidally disrupted.