100 research outputs found
5D gravity and the discrepant G measurements
It is shown that 5D Kaluza-Klein theory stabilized by an external bulk scalar
field may solve the discrepant laboratory G measurements. This is achieved by
an effective coupling between gravitation and the geomagnetic field.
Experimental considerations are also addressed.Comment: 13 pages, to be published in: Proceedings of the 18th Course of the
School on Cosmology and Gravitation: The gravitational Constant. Generalized
gravitational theories and experiments (30 April-10 May 2003, Erice). Ed. by
G. T. Gillies, V. N. Melnikov and V. de Sabbata, (Kluwer), 13pp. (in print)
(2003
Precision Measurement of the Newtonian Gravitational Constant Using Cold Atoms
About 300 experiments have tried to determine the value of the Newtonian
gravitational constant, G, so far, but large discrepancies in the results have
made it impossible to know its value precisely. The weakness of the
gravitational interaction and the impossibility of shielding the effects of
gravity make it very difficult to measure G while keeping systematic effects
under control. Most previous experiments performed were based on the torsion
pendulum or torsion balance scheme as in the experiment by Cavendish in 1798,
and in all cases macroscopic masses were used. Here we report the precise
determination of G using laser-cooled atoms and quantum interferometry. We
obtain the value G=6.67191(99) x 10^(-11) m^3 kg^(-1) s^(-2) with a relative
uncertainty of 150 parts per million (the combined standard uncertainty is
given in parentheses). Our value differs by 1.5 combined standard deviations
from the current recommended value of the Committee on Data for Science and
Technology. A conceptually different experiment such as ours helps to identify
the systematic errors that have proved elusive in previous experiments, thus
improving the confidence in the value of G. There is no definitive relationship
between G and the other fundamental constants, and there is no theoretical
prediction for its value, against which to test experimental results. Improving
the precision with which we know G has not only a pure metrological interest,
but is also important because of the key role that G has in theories of
gravitation, cosmology, particle physics and astrophysics and in geophysical
models.Comment: 3 figures, 1 tabl
Constraints on Non-Newtonian Gravity from Recent Casimir Force Measurements
Corrections to Newton's gravitational law inspired by extra dimensional
physics and by the exchange of light and massless elementary particles between
the atoms of two macrobodies are considered. These corrections can be described
by the potentials of Yukawa-type and by the power-type potentials with
different powers. The strongest up to date constraints on the corrections to
Newton's gravitational law are reviewed following from the E\"{o}tvos- and
Cavendish-type experiments and from the measurements of the Casimir and van der
Waals force. We show that the recent measurements of the Casimir force gave the
possibility to strengthen the previously known constraints on the constants of
hypothetical interactions up to several thousand times in a wide interaction
range. Further strengthening is expected in near future that makes Casimir
force measurements a prospective test for the predictions of fundamental
physical theories.Comment: 20 pages, crckbked.cls is used, to be published in: Proceedings of
the 18th Course of the School on Cosmology and Gravitation: The Gravitational
Constant. Generalized Gravitational Theories and Experiments (30 April- 10
May 2003, Erice). Ed. by G. T. Gillies, V. N. Melnikov and V. de Sabbata,
20pp. (Kluwer, in print, 2003
The Pioneer Anomaly
Radio-metric Doppler tracking data received from the Pioneer 10 and 11
spacecraft from heliocentric distances of 20-70 AU has consistently indicated
the presence of a small, anomalous, blue-shifted frequency drift uniformly
changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was
interpreted as a constant sunward deceleration of each particular spacecraft at
the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of
the Newton's gravitational inverse-square law has become known as the Pioneer
anomaly; the nature of this anomaly remains unexplained. In this review, we
summarize the current knowledge of the physical properties of the anomaly and
the conditions that led to its detection and characterization. We review
various mechanisms proposed to explain the anomaly and discuss the current
state of efforts to determine its nature. A comprehensive new investigation of
the anomalous behavior of the two Pioneers has begun recently. The new efforts
rely on the much-extended set of radio-metric Doppler data for both spacecraft
in conjunction with the newly available complete record of their telemetry
files and a large archive of original project documentation. As the new study
is yet to report its findings, this review provides the necessary background
for the new results to appear in the near future. In particular, we provide a
significant amount of information on the design, operations and behavior of the
two Pioneers during their entire missions, including descriptions of various
data formats and techniques used for their navigation and radio-science data
analysis. As most of this information was recovered relatively recently, it was
not used in the previous studies of the Pioneer anomaly, but it is critical for
the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living
Reviews in Relativit
Theorems on existence and global dynamics for the Einstein equations
This article is a guide to theorems on existence and global dynamics of
solutions of the Einstein equations. It draws attention to open questions in
the field. The local-in-time Cauchy problem, which is relatively well
understood, is surveyed. Global results for solutions with various types of
symmetry are discussed. A selection of results from Newtonian theory and
special relativity that offer useful comparisons is presented. Treatments of
global results in the case of small data and results on constructing spacetimes
with prescribed singularity structure or late-time asymptotics are given. A
conjectural picture of the asymptotic behaviour of general cosmological
solutions of the Einstein equations is built up. Some miscellaneous topics
connected with the main theme are collected in a separate section.Comment: Submitted to Living Reviews in Relativity, major update of Living
Rev. Rel. 5 (2002)
Theorems on existence and global dynamics for the Einstein equations
This article is a guide to theorems on existence and global dynamics of
solutions of the Einstein equations. It draws attention to open questions in
the field. The local in time Cauchy problem, which is relatively well
understood, is surveyed. Global results for solutions with various types of
symmetry are discussed. A selection of results from Newtonian theory and
special relativity which offer useful comparisons is presented. Treatments of
global results in the case of small data and results on constructing spacetimes
with prescribed singularity structure are given. A conjectural picture of the
asymptotic behaviour of general cosmological solutions of the Einstein
equations is built up. Some miscellaneous topics connected with the main theme
are collected in a separate section.Comment: 54 pages, submitted to Living Reviews in Relativit
Varying constants, Gravitation and Cosmology
Fundamental constants are a cornerstone of our physical laws. Any constant
varying in space and/or time would reflect the existence of an almost massless
field that couples to matter. This will induce a violation of the universality
of free fall. It is thus of utmost importance for our understanding of gravity
and of the domain of validity of general relativity to test for their
constancy. We thus detail the relations between the constants, the tests of the
local position invariance and of the universality of free fall. We then review
the main experimental and observational constraints that have been obtained
from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites
dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic
microwave background and big bang nucleosynthesis. At each step we describe the
basics of each system, its dependence with respect to the constants, the known
systematic effects and the most recent constraints that have been obtained. We
then describe the main theoretical frameworks in which the low-energy constants
may actually be varying and we focus on the unification mechanisms and the
relations between the variation of different constants. To finish, we discuss
the more speculative possibility of understanding their numerical values and
the apparent fine-tuning that they confront us with.Comment: 145 pages, 10 figures, Review for Living Reviews in Relativit
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Trans-specialization understanding in international technology alliances: The influence of cultural distance
In the information age, the firm's performance hinges on combining partners' specialist knowledge to achieve value co-creation. Combining knowledge from different specialties could be a costly process in the international technology alliances (ITAs) context. We argue that the combination of different specializations requires the development of "trans-specialization understanding" (TSU) instead of the internalization of partners' specialist knowledge. This article examines the extent to which inter-firm governance in ITAs shapes TSU, and whether the development of TSU is endangered by cultural distance. We hypothesize that relational governance, product modularity, and cultural distance influence TSU development, which in turn influences firm performance. We collected data from 110 non-equity ITAs between software and hardware firms participating in the mobile device sector. We analyzed the data using partial least squares path modeling. Our findings suggest that TSU largely depends on product modularity and relational governance in alliances. However, while cultural distance negatively moderates the path from relational governance to TSU, it has no effect on the relationship between product modularity and TSU. Based on this, we conclude that product modularity can substitute for relational governance when strong relational norms are not well-developed in international alliances. Thus cultural distance does not invariably amount to a liability in ITAs
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