7,609 research outputs found
Bounding the mass of the graviton using binary pulsar observations
The close agreement between the predictions of dynamical general relativity
for the radiated power of a compact binary system and the observed orbital
decay of the binary pulsars PSR B1913+16 and PSR B1534+12 allows us to bound
the graviton mass to be less than 7.6 x 10^{-20} eV with 90% confidence. This
bound is the first to be obtained from dynamic, as opposed to static-field,
relativity. The resulting limit on the graviton mass is within two orders of
magnitude of that from solar system measurements, and can be expected to
improve with further observations.Comment: 16 pages, 1 figure. Added appendix on other choices for mass ter
Swift Pointing and Gravitational-Wave Bursts from Gamma-Ray Burst Events
The currently accepted model for gamma-ray burst phenomena involves the
violent formation of a rapidly rotating solar-mass black hole. Gravitational
waves should be associated with the black-hole formation, and their detection
would permit this model to be tested. Even upper limits on the
gravitational-wave strength associated with gamma-ray bursts could constrain
the gamma-ray burst model. This requires joint observations of gamma-ray burst
events with gravitational and gamma-ray detectors. Here we examine how the
quality of an upper limit on the gravitational-wave strength associated with
gamma-ray bursts depends on the relative orientation of the gamma-ray-burst and
gravitational-wave detectors, and apply our results to the particular case of
the Swift Burst-Alert Telescope (BAT) and the LIGO gravitational-wave
detectors. A result of this investigation is a science-based ``figure of
merit'' that can be used, together with other mission constraints, to optimize
the pointing of the Swift telescope for the detection of gravitational waves
associated with gamma-ray bursts.Comment: iop style, 1 figure, 6 pages, presented at GWDAW 200
Epitaxial-strain-induced multiferroicity in SrMnO from first principles
First-principles density-functional calculations reveal a large spin-phonon
coupling in cubic SrMnO, with ferromagnetic ordering producing a polar
instability. Through combination of this coupling with the strain-polarization
coupling characteristic of perovskites, the bulk antiferromagnetic paraelectric
ground state of SrMnO is shown to be driven to a previously unreported
multiferroic ferroelectric-ferromagnetic state by increasing epitaxial strain,
both tensile and compressive. This state has a computed polarization and
estimated Curie temperature above 54 C/cm and 92 K. Large mixed
magnetic-electric-elastic responses are predicted in the vicinity of the phase
boundaries.Comment: 5 pages, 2 figures, 1 tabl
Event Rate for Extreme Mass Ratio Burst Signals in the LISA Band
Stellar mass compact objects in short period orbits about a
-- solar mass massive black hole (MBH) are thought to be a
significant continuous-wave source of gravitational radiation for the ESA/NASA
Laser Interferometer Space Antenna (LISA) gravitational wave detector. However,
these extreme mass-ratio inspiral sources began in long-period, nearly
parabolic orbits that have multiple close encounters with the MBH. The
gravitational radiation emitted during these close encounters may be detectable
by LISA as a gravitational wave burst if the characteristic passage timescale
is less than seconds. Scaling a static, spherical model to the size and
mass of the Milky Way bulge we estimate an event rate of ~ 15 per year for such
burst signals, detectable by LISA with signal-to-noise greater than five,
originating in our galaxy. When extended to include Virgo cluster galaxies our
estimate increases to a gravitational wave burst rate of ~ 18. We conclude that
these extreme mass-ratio burst sources may be a steady and significant source
of gravitational radiation in the LISA data streams.Comment: 4 pages, minor revisions. Accepted for ApJ Letter
Addressing LISA Science Analysis Challenges
The principal goal of the \emph{LISA Science Analysis Workshop} is to
encourage the development and maturation of science analysis technology in
preparation for LISA science operations. Exactly because LISA is a pathfinder
for a new scientific discipline -- gravitational wave astronomy -- LISA data
processing and science analysis methodologies are in their infancy and require
considerable maturation if they are to be ready to take advantage of LISA data.
Here we offer some thoughts, in anticipation of the LISA Science Analysis
Workshop, on analysis research problems that demonstrate the capabilities of
different proposed analysis methodologies and, simultaneously, help to push
those techniques toward greater maturity. Particular emphasis is placed on
formulating questions that can be turned into well-posed problems involving
tests run on specific data sets, which can be shared among different groups to
enable the comparison of techniques on a well-defined platform.Comment: 7 page
The Testbed for LISA Analysis Project
The Testbed for LISA Analysis (TLA) Project aims to facilitate the
development, validation and comparison of different methods for LISA science
data analysis, by the broad LISA Science Community, to meet the special
challenges that LISA poses. It includes a well-defined Simulated LISA Data
Product (SLDP), which provides a clean interface between the communities that
have developed to model and to analyze the LISA science data stream; a
web-based clearinghouse (at ) providing SLDP
software libraries, relevant software, papers and other documentation, and a
repository for SLDP data sets; a set of mailing lists for communication between
and among LISA simulators and LISA science analysts; a problem tracking system
for SLDP support; and a program of workshops to allow the burgeoning LISA
science community to further refine the SLDP definition, define specific LISA
science analysis challenges, and report their results. This note describes the
TLA Project, the resources it provides immediately, its future plans, and
invites the participation of the broader community in the furtherance of its
goals.Comment: 5 pages, no figure
Swift Pointing and the Association Between Gamma-Ray Bursts and Gravitational-Wave Bursts
The currently accepted model for gamma-ray burst phenomena involves the
violent formation of a rapidly rotating solar mass black hole. Gravitational
waves should be associated with the black-hole formation, and their detection
would permit this model to be tested, the black hole progenitor (e.g.,
coalescing binary or collapsing stellar core) identified, and the origin of the
gamma rays (within the expanding relativistic fireball or at the point of
impact on the interstellar medium) located. Even upper limits on the
gravitational-wave strength associated with gamma-ray bursts could constrain
the gamma-ray burst model. To do any of these requires joint observations of
gamma-ray burst events with gravitational and gamma-ray detectors. Here we
examine how the quality of an upper limit on the gravitational-wave strength
associated with gamma-ray burst observations depends on the relative
orientation of the gamma-ray-burst and gravitational-wave detectors, and apply
our results to the particular case of the Swift Burst-Alert Telescope (BAT) and
the LIGO gravitational-wave detectors. A result of this investigation is a
science-based ``figure of merit'' that can be used, together with other mission
constraints, to optimize the pointing of the Swift telescope for the detection
of gravitational waves associated with gamma-ray bursts.Comment: aastex, 14 pages, 2 figure
Nonlinear preferential rewiring in fixed-size networks as a diffusion process
We present an evolving network model in which the total numbers of nodes and
edges are conserved, but in which edges are continuously rewired according to
nonlinear preferential detachment and reattachment. Assuming power-law kernels
with exponents alpha and beta, the stationary states the degree distributions
evolve towards exhibit a second order phase transition - from relatively
homogeneous to highly heterogeneous (with the emergence of starlike structures)
at alpha = beta. Temporal evolution of the distribution in this critical regime
is shown to follow a nonlinear diffusion equation, arriving at either pure or
mixed power-laws, of exponents -alpha and 1-alpha
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