18 research outputs found
Static post-Newtonian equivalence of GR and gravity with a dynamical preferred frame
A generally covariant extension of general relativity (GR) in which a
dynamical unit timelike vector field is coupled to the metric is studied in the
asymptotic weak field limit of spherically symmetric static solutions. The two
post-Newtonian parameters known as the Eddington-Robertson-Schiff parameters
are found to be identical to those in the case of pure GR, except for some
non-generic values of the coefficients in the Lagrangian.Comment: 13 pages; v.2: minor editing, signs corrected, version to appear in
PRD; v. 3: signs corrected in eqn (3
Implementation of Time-Delay Interferometry for LISA
We discuss the baseline optical configuration for the Laser Interferometer
Space Antenna (LISA) mission, in which the lasers are not free-running, but
rather one of them is used as the main frequency reference generator (the {\it
master}) and the remaining five as {\it slaves}, these being phase-locked to
the master (the {\it master-slave configuration}). Under the condition that the
frequency fluctuations due to the optical transponders can be made negligible
with respect to the secondary LISA noise sources (mainly proof-mass and shot
noises), we show that the entire space of interferometric combinations LISA can
generate when operated with six independent lasers (the {\it one-way method})
can also be constructed with the {\it master-slave} system design. The
corresponding hardware trade-off analysis for these two optical designs is
presented, which indicates that the two sets of systems needed for implementing
the {\it one-way method}, and the {\it master-slave configuration}, are
essentially identical. Either operational mode could therefore be implemented
without major implications on the hardware configuration. We then.......Comment: 39 pages, 6 figures, 2 table
Effects of finite arm-length of LISA on analysis of gravitational waves from MBH binaries
Response of an interferometer becomes complicated for gravitational wave
shorter than the arm-length of the detector, as nature of wave appears
strongly. We have studied how parameter estimation for merging massive black
hole binaries are affected by this complicated effect in the case of LISA. It
is shown that three dimensional positions of some binaries might be determined
much better than the past estimations that use the long wave approximation. For
equal mass binaries this improvement is most prominent at \sim 10^5\sol.Comment: 10 pages, 3 figures, to appear in Phys.Rev.
Optimal filtering of the LISA data
The LISA time-delay-interferometry responses to a gravitational-wave signal
are rewritten in a form that accounts for the motion of the LISA constellation
around the Sun; the responses are given in closed analytic forms valid for any
frequency in the band accessible to LISA. We then present a complete procedure,
based on the principle of maximum likelihood, to search for stellar-mass binary
systems in the LISA data. We define the required optimal filters, the
amplitude-maximized detection statistic (analogous to the F statistic used in
pulsar searches with ground-based interferometers), and discuss the false-alarm
and detection probabilities. We test the procedure in numerical simulations of
gravitational-wave detection.Comment: RevTeX4, 28 pages, 9 EPS figures. Minus signs fixed in Eq. (46) and
Table II. Corrected discussion of F-statistic distribution in Sec. IV
Higher Dimensional Dark Energy Investigation with Variable and
Time variable and are studied here under a phenomenological
model of through an () dimensional analysis. The relation of
Zeldovich (1968) between and is
employed here, where is the proton mass and is Planck's constant. In
the present investigation some key issues of modern cosmology, viz. the age
problem, the amount of variation of and the nature of expansion of the
Universe have been addressed.Comment: 7 Latex pages with few change
Pulsar timing arrays and the challenge of massive black hole binary astrophysics
Pulsar timing arrays (PTAs) are designed to detect gravitational waves (GWs)
at nHz frequencies. The expected dominant signal is given by the superposition
of all waves emitted by the cosmological population of supermassive black hole
(SMBH) binaries. Such superposition creates an incoherent stochastic
background, on top of which particularly bright or nearby sources might be
individually resolved. In this contribution I describe the properties of the
expected GW signal, highlighting its dependence on the overall binary
population, the relation between SMBHs and their hosts, and their coupling with
the stellar and gaseous environment. I describe the status of current PTA
efforts, and prospect of future detection and SMBH binary astrophysics.Comment: 18 pages, 4 figures. To appear in the Proceedings of the 2014 Sant
Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed.
C.Sopuerta (Berlin: Springer-Verlag
Pulsar Timing and its Application for Navigation and Gravitational Wave Detection
Pulsars are natural cosmic clocks. On long timescales they rival the
precision of terrestrial atomic clocks. Using a technique called pulsar timing,
the exact measurement of pulse arrival times allows a number of applications,
ranging from testing theories of gravity to detecting gravitational waves. Also
an external reference system suitable for autonomous space navigation can be
defined by pulsars, using them as natural navigation beacons, not unlike the
use of GPS satellites for navigation on Earth. By comparing pulse arrival times
measured on-board a spacecraft with predicted pulse arrivals at a reference
location (e.g. the solar system barycenter), the spacecraft position can be
determined autonomously and with high accuracy everywhere in the solar system
and beyond. We describe the unique properties of pulsars that suggest that such
a navigation system will certainly have its application in future astronautics.
We also describe the on-going experiments to use the clock-like nature of
pulsars to "construct" a galactic-sized gravitational wave detector for
low-frequency (f_GW ~1E-9 - 1E-7 Hz) gravitational waves. We present the
current status and provide an outlook for the future.Comment: 30 pages, 9 figures. To appear in Vol 63: High Performance Clocks,
Springer Space Science Review
Gravitational Radiation Theory and Light Propagation
The paper gives an introduction to the gravitational radiation theory of isolated sources and to the propagation properties of light rays in radiative gravitational fields. It presents a theoretical study of the generation, propagation, back-reaction, and detection of gravitational waves from astrophysical sources. After reviewing the various quadrupole-moment laws for gravitational radiation in the Newtonian approximation, we show how to incorporate post-Newtonian corrections into the source multipole moments, the radiative multipole moments at infinity, and the back-reaction potentials. We further treat the light propagation in the linearized gravitational field outside a gravitational wave emitting source. The effects of time delay, bending of light, and moving source frequency shift are presented in terms of the gravitational lens potential. Time delay results are applied in the description of the procedure of the detection of gravitational waves
Flight demonstration of FEEP on Get Away Special
Primarily intended for verification of the thruster design and assessment of actual performance, the FEEP thruster flight demonstration (EMITS - Electrical MIcrothruster Test in Space) is aimed at building confidence in this new technology among the potential commercial and scientific users. EMITS will exploit an existing ESA-NASA agreement for the utilization of the Get Away Special (GAS) facility to fly a package including two thrusters of different thrust levels (30 μN and 1 mN), the thruster power and control electronics unit, a computerized experiment control and data storage unit, and a battery. The main goal of the experiment is the verification of in-orbit ion beam production, neutralization and throttling. Other goals include ion beam shape investigation and monitoring of propellant deposition on the nearby surfaces. This paper presents the EMITS configuration and goals and outlines the experiment main features
STEP: Satellite Test of the Equivalence Principle. Report on the Phase A Study
Report of the STEP mission study at Phase A level (conducted jointly by ESA and Nasa). Nobili A.M. was member of ESA science tea