2,697 research outputs found
Translation invariant time-dependent solutions to massive gravity
Homogeneous time-dependent solutions of massive gravity generalise the plane
wave solutions of the linearised Fierz-Pauli equations for a massive spin-two
particle, as well as the Kasner solutions of General Relativity. We show that
they also allow a clear counting of the degrees of freedom and represent a
simplified framework to work out the constraints, the equations of motion and
the initial value formulation. We work in the vielbein formulation of massive
gravity, find the phase space resulting from the constraints and show that
several disconnected sectors of solutions exist some of which are unstable. The
initial values determine the sector to which a solution belongs. Classically,
the theory is not pathological but quantum mechanically the theory may suffer
from instabilities. The latter are not due to an extra ghost-like degree of
freedom.Comment: 31 page
Translation invariant time-dependent solutions to massive gravity II
This paper is a sequel to arXiv:1310.6560 [hep-th] and is also devoted to
translation-invariant solutions of ghost-free massive gravity in its moving
frame formulation. Here we consider a mass term which is linear in the vielbein
(corresponding to a term in the 4D metric formulation) in addition to
the cosmological constant. We determine explicitly the constraints, and from
the initial value formulation show that the time-dependent solutions can have
singularities at a finite time. Although the constraints give, as in the
case, the correct number of degrees of freedom for a massive spin two
field, we show that the lapse function can change sign at a finite time causing
a singular time evolution. This is very different to the case where
time evolution is always well defined. We conclude that the mass term
can be pathological and should be treated with care.Comment: 19 pages, 1 figur
Deformations of Differential Calculi
It has been suggested that quantum fluctuations of the gravitational field
could give rise in the lowest approximation to an effective noncommutative
version of Kaluza-Klein theory which has as extra hidden structure a
noncommutative geometry. It would seem however from the Standard Model, at
least as far as the weak interactions are concerned, that a double-sheeted
structure is the phenomenologically appropriate one at present accelerator
energies. We examine here to what extent this latter structure can be
considered as a singular limit of the former.Comment: 11 pages of Late
The Need to Support of Data Flow Graph Visualization of Forensic Lucid Programs, Forensic Evidence, and their Evaluation by GIPSY
Lucid programs are data-flow programs and can be visually represented as data
flow graphs (DFGs) and composed visually. Forensic Lucid, a Lucid dialect, is a
language to specify and reason about cyberforensic cases. It includes the
encoding of the evidence (representing the context of evaluation) and the crime
scene modeling in order to validate claims against the model and perform event
reconstruction, potentially within large swaths of digital evidence. To aid
investigators to model the scene and evaluate it, instead of typing a Forensic
Lucid program, we propose to expand the design and implementation of the Lucid
DFG programming onto Forensic Lucid case modeling and specification to enhance
the usability of the language and the system and its behavior. We briefly
discuss the related work on visual programming an DFG modeling in an attempt to
define and select one approach or a composition of approaches for Forensic
Lucid based on various criteria such as previous implementation, wide use,
formal backing in terms of semantics and translation. In the end, we solicit
the readers' constructive, opinions, feedback, comments, and recommendations
within the context of this short discussion.Comment: 11 pages, 7 figures, index; extended abstract presented at VizSec'10
at http://www.vizsec2010.org/posters ; short paper accepted at PST'1
On Tachyon kinks from the DBI action
We consider solitonic solutions of the DBI tachyon effective action for a
non-BPS brane in the presence of an electric field. We find that for a constant
electric field , regular solitons compactified on a circle admit
a singular and decompactified limit corresponding to Sen's proposal provided
the tachyon potential satisfies some restrictions. On the other hand for the
critical electric field , regular and finite energy solitons are
constructed without any restriction on the potential.Comment: proceedings of the second string phenomenology conference, Durham,
30th July to 4th August 200
Detailed gravity anomalies from GEOS-3 satellite altimetry data
A technique for deriving mean gravity anomalies from dense altimetry data was developed. A combination of both deterministic and statistical techniques was used. The basic mathematical model was based on the Stokes' equation which describes the analytical relationship between mean gravity anomalies and geoid undulations at a point; this undulation is a linear function of the altimetry data at that point. The overdetermined problem resulting from the excessive altimetry data available was solved using Least-Squares principles. These principles enable the simultaneous estimation of the associated standard deviations reflecting the internal consistency based on the accuracy estimates provided for the altimetry data as well as for the terrestrial anomaly data. Several test computations were made of the anomalies and their accuracy estimates using GOES-3 data
Applications of satellite and marine geodesy to operations in the ocean environment
The requirements for marine and satellite geodesy technology are assessed with emphasis on the development of marine geodesy. Various programs and missions for identification of the satellite geodesy technology applicable to marine geodesy are analyzed along with national and international marine programs to identify the roles of satellite/marine geodesy techniques for meeting the objectives of the programs and other objectives of national interest effectively. The case for marine geodesy is developed based on the extraction of requirements documented by authoritative technical industrial people, professional geodesists, government agency personnel, and applicable technology reports
The significance of the Skylab altimeter experiment results and potential applications
The Skylab Altimeter Experiment has proven the capability of the altimeter for measurement of sea surface topography. The geometric determination of the geoid/mean sea level from satellite altimetry is a new approach having significant applications in many disciplines including geodesy and oceanography. A Generalized Least Squares Collocation Technique was developed for determination of the geoid from altimetry data. The technique solves for the altimetry geoid and determines one bias term for the combined effect of sea state, orbit, tides, geoid, and instrument error using sparse ground truth data. The influence of errors in orbit and a priori geoid values are discussed. Although the Skylab altimeter instrument accuracy is about + or - 1 m, significant results were obtained in identification of large geoidal features such as over the Puerto Rico trench. Comparison of the results of several passes shows that good agreement exists between the general slopes of the altimeter geoid and the ground truth, and that the altimeter appears to be capable of providing more details than are now available with best known geoids. The altimetry geoidal profiles show excellent correlations with bathymetry and gravity. Potential applications of altimetry results to geodesy, oceanography, and geophysics are discussed
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