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Date, time and place
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Speaker, affiliation, title and abstract
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JSI
mini-symposium
Friday Sep. 16,
2:00-6:00pm.
Room 2400 Computer
and Space Sciences Building
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"JSI Scientists Overview"
Bernard Kelly (NASA
Goddard): "Gravitational-wave data analysis with
spinning merger-ringdown waveforms"
Yi Pan (UMD):
"Expanding effective-one-body models in binary
black hole parameter space"
Scott Field (UMD): "A reduced basis
representation for chirp and ringdown
gravitational wave templates"
Tyson Littenberg (NASA Goddard and UMD):
"White dwarf binary science in the post-LISA
era"
Tamara Bogdanovic (UMD): "Electromagnetic
Signatures of Supermassive Black Hole Mergers"
Margaret Trippe (UMD): "Our Spin on Supermassive
Black Holes"
Simona Giacintucci (UMD): "Diffuse radio
emission from the intracluster medium - the low
frequency viewpoint"
David B. Fisher (UMD): "Bulges in the Nearby
Universe"
Alexandre Le Tiec (UMD): "Periastron Advance in
Black Hole Binaries"
Sam Gralla (UMD): "Gravitational Self-Force in
Extreme Mass-Ratio Inspiral"
James Van Meter (NASA Goddard): "Invariant
computation of spin and other properties of
numerically simulated black holes"
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Astro
Theory Lunch
Monday, Sep. 26
11:30am
1255 (Library
room) CSS (Computer and Space Sciences)
Building
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Umberto Cannella
Department of
Physics, University of Maryland
"Testing gravity
with gravitational waves: a field-theoretical
perspective"
Abstract: So far
experiments of relativistic gravity have probed
dynamical regimes only up to order "(v/c)^5" in
the post-Newtonian expansion, which corresponds
to the very first term of the radiative sector
in General Relativity. In contrast, by means of
gravitational-wave astronomy, one aims at
testing gravity up to (v/c)^(12)! It is then
relevant to envisage testing frameworks which
are appropriate to this strong-field/radiative
regime.
Using a field
theory approach, gravitational interactions are
described by Feynman diagrams in which classical
gravitons interact with matter sources and among
themselves. Tagging the self-interaction
vertices of gravitons with parameters it is
possible, for example, to translate the measure
of the period decay of Hulse-Taylor pulsar into
a constraint on the three-graviton vertex at the
0.1% level. With future observations of
gravitational waves, higher order graviton
vertices can in principle be constrained through
a Fisher matrix analysis.
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Monday, Sep. 26
1:30pm
Room 4102
Physics
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Bruno Giacomazzo
Department of
Astronomy, University of Maryland, and NASA
Goddard
"Magnetized
binary neutron stars"
Abstract:
Binary neutron stars are among the most
powerful sources of gravitational waves
that will be detected by ground-based
interferometers, such as advanced Virgo
and LIGO, and they are also thought to be
behind the central engine of short
gamma-ray bursts. I will report on the
work I have done in the last two years by
using my fully general relativistic
magnetohydrodynamic code Whisky in
simulating binary neutron star systems
during the last stages of inspiral, merger
and eventual collapse to a black hole
surrounded by an hot and magnetized torus.
I will in particular describe the
gravitational wave signal emitted by these
sources and their possible role in
powering short gamma-ray bursts.
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EPT
Seminar
Monday, Sep. 26
3:00pm
Room 4102
Physics
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Yasunori Nomura
University of
California, Berkeley
"Physical
Predictions in the Quantum Multiverse"
Abstract: I
describe how quantum mechanics plays a crucial
role in defining probabilities (the "measure")
in the multiverse. The resulting picture leads
to a dramatic change of our view on spacetime
and gravity, and provides complete unification
of the eternally inflating multiverse and many
worlds in quantum mechanics. The latest result
on the distribution of the cosmological constant
is also presented. The talk is based mainly on
arXiv:1104.2324 (but also on arXiv:1107.3556).
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MCFP
Colloquium
Thursday, Sep. 29
4:00pm
Room 1201
Physics
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Sergei Dubovsky
New York University
"Exploring the
String Axiverse with Astrophysical Black
Holes?"
Abstract: Combining
the QCD axion as a solution to the strong CP
problem with the properties of axions in string
theory suggests the simultaneous presence of
many ultralight axions with masses homogeneously
distributed over the log scale---the "Axiverse".
These axions give rise to a number of
distinctive observational signatures, including
the rotation of the CMB polarizations at the
level within the reach of the Planck satellite,
and steps in the dark matter power spectrum. A
surprising evidence for the axions with masses
in the range 10^(-22) to 10^(-10) eV may come
from observations of astrophysical black holes
through the Penrose superradiance process. When
the axion Compton wavelength is of order of the
black hole size, the axions develop
"superradiant" atomic bound states around the
black hole "nucleus". Their occupation number
grows exponentially by extracting rotational
energy from the ergosphere, culminating in a
rotating Bose-Einstein axion condensate emitting
gravitational waves. This mechanism creates mass
gaps in the spectrum of rapidly rotating black
holes and gives rise to a distinctive gravity
wave signal. In particular, the QCD axion with
the decay constant of order the GUT scale
affects the dynamics of stellar mass black
holes. This opens a possibility for a discovery
of the QCD axions through ongoing measurements
of black hole spins. The corresponding gravity
wave signal may be within the reach of the
Advanced LIGO.
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Astro Theory
Lunch
Monday, Oct. 3
11:30am
1255 (Library
room) CSS (Computer and Space Sciences)
Building
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Laura Blecha,
Harvard University
"Signatures of
Supermassive Black Hole Mergers: Before and
After"
Abstract: Because
central supermassive black holes (SMBHs) are
ubiquitous in local galaxies, SMBH pairs are
expected to form in major galaxy mergers. Until
recently, however, few observational constraints
existed on the population of SMBH pairs. Even
less is known empirically about their subsequent
evolution to a possible merger and
gravitational-wave recoil kick. I will review
the remarkable recent progress in finding
candidate SMBH pairs, as well as recent
identifications of candidate recoiling SMBHs. I
will then describe our efforts to interpret
these findings and make predictions for future
observations using hydrodynamic simulations of
galaxy mergers that include SMBHs. Specifically,
I will focus on 1) kpc-scale SMBH pairs and 2)
recoiling SMBHs. Because many candidate SMBH
pairs have been identified as double-peaked
narrow-line (NL) AGN, we have made a first
attempt to model the NL region in galaxy merger
simulations. In general, we find that
double-peaked NL AGN occur as a short-lived but
generic phase of gaseous major mergers, and that
they originate from a varied combination of SMBH
motion and gas kinematics. I will discuss the
implications of our findings for follow-up
confirmation of candidate SMBH pairs.
Additionally, I will summarize the results of
our large study of recoiling SMBHs in galaxy
merger simulations. I will describe the dynamics
of recoil in gas-rich versus gas-poor mergers,
as well as the possible effects of recoil on
star formation and the black hole - bulge
relations. Recoiling SMBHs may be observed as
kinematically- or spatially-offset AGN with
lifetimes of up to tens of Myr; I will conclude
by describing efforts to model a candidate
recoiling SMBH that displays both types of
offset.
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Monday, Oct. 3
Joint
seminar with Particle Theory
3:00pm
Room 4102 Physics
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Alejandro Satz
Department of Physics, University of Maryland
"Nonlocalities in the Quantum Gravity effective
action renormalization flow"
Abstract: The renormalization group flow of the
effective average action has been intensively
studied in quantum gravity with the hope of
exhibiting a non-Gaussian fixed point that renders
the theory asymptotically safe. To make concrete
calculations possible, most research has focused
upon truncations of the effective action
restricting it to local terms. In this talk I
present some preliminary results concerning the RG
flow of nonlocal terms, within a one-loop
approximation and in a weak field expansion. The
flowing nonlocal effective action reduces to the
standard effective action of low-energy
perturbative quantum gravity in the appropiate
limit, and can be used to compute quantum
corrections to the Newtonian potential, which will
be described and discussed.
(based
on http://arxiv.org/abs/1006.3808)
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Monday, Oct. 3
Ph D
thesis defense
4:00pm
Place: 4316 Physics
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Jonah Kanner
Department of Physics, University of Maryland
"LOOC UP: Seeking Optical Counterparts to
Gravitational Wave Signals"
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Monday, Oct. 10
1:30pm
Room 4102 Physics
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Sarah Caudill
Department of Physics and Astronomy, Louisiana
State University
"Reduced Basis
representations of multi-mode black hole
ringdown gravitational waves"
Abstract: The search for ringdown
gravitational waves with LIGO currently
utilizes single mode templates to detect the
least damped quasinormal mode (QNM) from a
perturbed intermediate mass black hole.
However, a single mode template search for
these black holes (M>100 solar masses) can
miss more than 10% of events in both LIGO and
advanced ground-based detectors. This loss of
events can be remedied with a two-mode
template search. However, the number of
templates needed for a constrained two-mode
search with a minimal match of 99% can be as
high as 1.8e4. Nevertheless, we demonstrate
that we can construct compact and high
accuracy reduced basis (RB) representations of
single and multiple QNMs and dramatically
compress the template banks used for ringdown
searches. Furthermore, we find that the RB
waveforms are able to represent any ringdown
waveform within the parameter space to
extremely high accuracy, typically less than
1e-13. I will discuss other details of this
study (arXiv:1109.5642v1) and how these
results open the possibility of searches of
multi-mode ringdown gravitational waves.
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EPT Seminar
Monday, Oct. 10
3:00pm
Room 4102 Physics
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Roni Harnik,
Fermilab
"CMB signals from
our Parent Vacuum"
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Monday, Oct. 17
1:30pm
Room 4102
Physics
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Sam Gralla
Department of
Physics, University of Maryland
"Motion of Small
Bodies: Derivation and Surprises"
Astract: A formalism developed jointly with R
Wald has proven remarkably successful in
(rigorously) deriving equations of motion for
"small bodies" in General Relativity and other
classical field theories. The basic idea
is to consider a one-parameter-family of
spacetimes in which not only the size of the
body but also its mass and charges are taken to
zero, a limit which is physical in the sense
that it respects the Schwarzschild limit on the
size of a body and keeps the self-energy finite,
and mathematically convenient in that it avoids
the usual difficulties with point
particles. I will describe the formalism
and its application to 1) self-force and
spin-force effects in general relativity, 2)
self, spin and dipole forces in classical
electromagnetism, and 3) lowest-order motion in
a general diffeomorphism-covariant Lagrangian
field theory. Some of the surprises have
been: a key role played by a "parity condition"
due to Regge and Teitelboim, a universal form
for the equation of motion across Lagrangian
field theories, the appearance of "extra terms"
in the force on a classical electric or magnetic
dipole, and the existence of a "kinematical
effect" that modifies the motion of all spinning
bodies, giving rise to "bobbing behavior" (as
observed in simulations of spinning black hole
binaries) in ordinary systems like billiard
balls connected by a string.
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Astro Theory Lunch
Monday, Oct. 24
11:00am
1255 (Library
room) CSS (Computer and Space Sciences)
Building
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KwangHo Park,
Department of
Astronomy, University of Maryland
"Accretion onto
Black Holes from Large Scales Regulated by
Radiative Feedback : Growth Rate and Duty Cycle"
Abstract:
We present
simulations of radiation-regulated accretion
onto black holes from galactic scales. We find
that the thermal pressure of the ionized sphere
forming around the black hole is the dominant
mechanism regulating the accretion rate,
producing periodic and short-lived luminosity
burst. We also focus on the effects of radiation
pressure and gas angular momentum on the black
hole growth rate and duty cycle. Our simulations
focus on intermediate-mass black hole, but we
derive general scaling relationships that are
solutions of the classic Bondi problem when
radiation feedback is considered. We found two
distinct modes of oscillations with very
different duty cycles, governed by different
depletion processes of the gas inside the
ionized bubble.
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Monday, Oct. 24
1:30pm
Room 4102 Physics
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Umberto Cannella
Department of
Physics, University of Maryland
"Testing gravity
with gravitational waves - a field-theoretical
perspective"
Abstract: So far experiments of relativistic
gravity have probed dynamical regimes only up to
order "(v/c)^5" in the post-Newtonian expansion,
which corresponds to the very first term of the
radiative sector in General Relativity. In
contrast, by means of gravitational-wave
astronomy, one aims at testing gravity up to
(v/c)^(12)! It is then relevant to envisage
testing frameworks which are appropriate to this
strong-field/radiative regime. Using a field
theoretical approach, gravitational interactions
are described by Feynman diagrams in which
classical gravitons interact with matter sources
and among themselves. Tagging the
self-interaction vertices of gravitons with
parameters it is possible, for example, to
translate the measure of the period decay of
Hulse-Taylor pulsar into a constraint on the
three-graviton vertex at the 0.1% level. The
resulting framework is a relevant example of how
to meaningfully constrain gravity in the
strong-field/radiative regime.
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Monday, Oct. 31
1:30pm
Room 4102
Physics
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Tamara
Bogdanovic
Department of
Astronomy, University of Maryland
"Electromagnetic
Signatures of Supermassive Black Hole Mergers"
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JSI mini-symposium
Friday Nov. 4,
2:00-6:00pm.
NASA Goddard
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"Accretion
and particle acceleration"
1:00 or 1:30 (to be confirmed) - 2:00 catered
lunch
2:00-2:30
"Basics of accretion disks", Chris Reynolds
2:30-3:00 Discussion
3:00-3:30 break
3:30-4:00 "Basics of plasma physics and
particle acceleration", Jim Drake
4:00-4:30 Discussion
4:30-5:00 break
5:00-5:30 "Basics of dynamical strong
gravity, matter, and magnetic
fields", John Baker
5:30-6:00 Discussion
End of
minisymposium
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Monday, Nov. 7
1:30pm
Room 4102
Physics
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Jennifer Seiler
NASA Goddard
"Binary Orbital Dynamics from Analysis of
Spherical Harmonic Modes of
Gravitational Waves"
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 well-know 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.
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Monday, Nov. 14
1:30pm
Room 4102 Physics
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Monday, Nov. 28
1:30pm
Room 4102
Physics
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Liangcheng Tu
Huazhong
University of Science and Technology,
Wuhan, China
"Progress in
testing Newtonian inverse square law in
short range with dual-modulation torsion
balance"
Abstract:
This talk
will have two parts: a brief introduction
of the HUST Gravitation Experiment Group
and a detailed report of the Newtonian
inverse square law (ISL) tests that have
been performed and are being performed in
the HUST group. In the
second part, first, general motivation
and the current status of the ISL test
at short range will be discussed; then,
our experiments at sub-millimeter to
millimeter range will be
introduced. We use a torsion
balance to sense the force from a
gap-modulated source. The goal of
the experiment is to improve the limit
of the ISL by at least an order of
magnitude. Finally, our future
experimental schemes, to test the ISL at
micrometer to sub-millimeter range with
a density modulated source and a torsion
balance with AFM, will be presented.
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Joint GR-Math
Numerical Analysis Seminar.
Tuesday, Nov. 29
3:30pm
MATH 3206
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Jorg
Frauendiener
Department
of Mathematics and Statistics,
University of Otago, New
Zealand
"Exploring
the corner: numerical
relativity near space-like
infinity"
Abstract:
Numerical Relativity has made
tremendous advances over the
last decade. However, there
are still some issues which
need clarification. One of
these is the question of the
outer boundary. It is well
known that modeling an
infinite domain using a finite
outer boundary creates
problems, not only numerically
but even more so conceptually.
A partial solution of this
issue is obtained by focussing
on the hyperboloidal initial
value problem using the
conformal field equations or
by regularising the equations
at infinity. This still leaves
the problem of having to
specify hyperboloidal initial
data in contrast to
asymptotically Euclidean data
based on a Cauchy hypersurface
(that we might be more used
to) and one needs to find a
way of connecting data on a
Cauchy surface with those on a
hyperboloidal hypersurface. In
this talk I will describe a
particular attempt to tackle
this problem based on methods
developed by H. Friedrich.
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Monday, Dec. 5
1:30pm
Room 4102
Physics
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Monday, Dec. 12
1:30pm
Room 4102
Physics
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Alexandre Le Tiec
Department of Physics, University of Maryland
"The first law of binary black hole mechanics"
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