577 research outputs found
Search for transient ultralight dark matter signatures with networks of precision measurement devices using a Bayesian statistics method
We analyze the prospects of employing a distributed global network of
precision measurement devices as a dark matter and exotic physics observatory.
In particular, we consider the atomic clocks of the Global Positioning System
(GPS), consisting of a constellation of 32 medium-Earth orbit satellites
equipped with either Cs or Rb microwave clocks and a number of Earth-based
receiver stations, some of which employ highly-stable H-maser atomic clocks.
High-accuracy timing data is available for almost two decades. By analyzing the
satellite and terrestrial atomic clock data, it is possible to search for
transient signatures of exotic physics, such as "clumpy" dark matter and dark
energy, effectively transforming the GPS constellation into a 50,000km aperture
sensor array. Here we characterize the noise of the GPS satellite atomic
clocks, describe the search method based on Bayesian statistics, and test the
method using simulated clock data. We present the projected discovery reach
using our method, and demonstrate that it can surpass the existing constrains
by several order of magnitude for certain models. Our method is not limited in
scope to GPS or atomic clock networks, and can also be applied to other
networks of precision measurement devices.Comment: See also Supplementary Information located in ancillary file
Search for domain wall dark matter with atomic clocks on board global positioning system satellites
Cosmological observations indicate that 85% of all matter in the Universe is
dark matter (DM), yet its microscopic composition remains a mystery. One
hypothesis is that DM arises from ultralight quantum fields that form
macroscopic objects such as topological defects. Here we use GPS as a ~ 50,000
km aperture DM detector to search for such defects in the form of domain walls.
GPS navigation relies on precision timing signals furnished by atomic clocks
hosted on board GPS satellites. As the Earth moves through the galactic DM
halo, interactions with topological defects could cause atomic clock glitches
that propagate through the GPS satellite constellation at galactic velocities ~
300 km/s. Mining 16 years of archival GPS data, we find no evidence for DM in
the form of domain walls at our current sensitivity level. This allows us to
improve the limits on certain quadratic scalar couplings of domain wall DM to
standard model particles by several orders of magnitude.Comment: 7 pages (main text), and 12 pages for Supplementary Information. v3:
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Letter from Graham Blewitt to M. Cherif Bassiouni
Letter from Graham Blewitt to M. Cherif Bassiouni regarding meeting with Lt-Col. Kempenaars and Bill Schiller and attaching Bassiouni\u27s List of Material Delivered to the Prosecutor\u27s Office of the International Tribunal on Friday 25 February 1994https://scholarlycommons.law.case.edu/documents_780/1048/thumbnail.jp
A study of atmospheric neutrinos with the IMB detector
A sample of 401 contained neutrino interactions collected in the 3300 metric ton fiducial mass IMB detector was used to study neutrino oscillations, geomagnetic modulation of the flux and to search for point sources. The majority of these events are attributed to neutrino interactions. For the most part, these neutrinos are believed to originate as tertiary products of cosmic ray interactions in the atmosphere. The neutrinos are a mixture of v sub e and v sub micron
Killer whale (Orcinus orca) predation on beaked whales (Mesoplodon spp.) in the Bremer Sub-Basin, Western Australia
Observations of killer whales (Orcinus orca) feeding on the remains of beaked whales have been previously documented; however, to date, there has been no published account of killer whales actively preying upon beaked whales. This article describes the first field observations of killer whales interacting with, hunting and preying upon beaked whales (Mesoplodon spp.) on four separate occasions during 2014, 2015 and 2016 in the Bremer Sub-Basin, off the south coast of Western Australia
The Spring 1985 high precision baseline test of the JPL GPS-based geodetic system
The Spring 1985 High Precision Baseline Test (HPBT) was conducted. The HPBT was designed to meet a number of objectives. Foremost among these was the demonstration of a level of accuracy of 1 to 2:10 to the 7th power, or better, for baselines ranging in length up to several hundred kilometers. These objectives were all met with a high degree of success, with respect to the demonstration of system accuracy in particular. The results from six baselines ranging in length from 70 to 729 km were examined for repeatability and, in the case of three baselines, were compared to results from colocated VLBI systems. Repeatability was found to be 5:10 to the 8th power (RMS) for the north baseline coordinate, independent of baseline length, while for the east coordinate RMS repeatability was found to be larger than this by factors of 2 to 4. The GPS-based results were found to be in agreement with those from colocated VLBI measurements, when corrected for the physical separations of the VLBI and CPG antennas, at the level of 1 to 2:10 to the 7th power in all coordinates, independent of baseline length. The results for baseline repeatability are consistent with the current GPA error budget, but the GPS-VLBI intercomparisons disagree at a somewhat larger level than expected. It is hypothesized that these differences may result from errors in the local survey measurements used to correct for the separations of the GPS and VLBI antenna reference centers
Improved treatment of global positioning system force parameters in precise orbit determination applications
Data collected from a worldwide 1992 experiment were processed at JPL to determine precise orbits for the satellites of the Global Positioning System (GPS). A filtering technique was tested to improve modeling of solar-radiation pressure force parameters for GPS satellites. The new approach improves orbit quality for eclipsing satellites by a factor of two, with typical results in the 25- to 50-cm range. The resultant GPS-based estimates for geocentric coordinates of the tracking sites, which include the three DSN sites, are accurate to 2 to 8 cm, roughly equivalent to 3 to 10 nrad of angular measure
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