1. Testing alternative theories of gravitation with superconducting gravimeters
8th January 2008 Taitung workshop
Sachie Shiomi
Space Geodesy Laboratory,
Department of Civil Engineering,
National Chiao Tung University,
Hsinchu, Taiwan

2. Contents Introduction Improving previous geophysical tests
Superconducting Gravimeters (SGs)
The global network of SGs
Improving previous geophysical tests
Search for spatial anisotropy in G
Search for gravitational waves
Future works
Conclusions and summary

3. Superconducting gravimeter (SG)
Hsinchu SG, operated by NCTU and CMS

4. Sensitive and stable Sensitivity Better than 1 ngal (10-11 ms-2)
Instrumental drift
Less than
1 μgal/year
(10-8 ms-2/year)
J. M. Goodkind, Review of Scientific Instruments 70 (1999)

5. Global network of superconducting gravimeters
Since 1997
Currently operating
Stopped
To be installed
Newly installed
D. Crossley

6. Improvements in gravity measurements
Development of the instruments.
Improvement by ~1000 from early 1970’s
Development of the global network.
Multistation analysis
Coincidence measurements
Improved knowledge on disturbances.

7. Spatial anisotropies in G
Preferred frame effects (α2)
Translation and rotation of the Earth relative to the preferred frames
Preferred location effects (ξ)
A nearby gravitating body (e.g. Galaxy)
Anomalous tidal effects:△g/g
Will 1971 Astro.J.

8. Experimental upper limits
Preferred frame: α2
Preferred location: ξ
Will (1971)
3×10-2
10-2
Warburton & Goodkind (1976)
4×10-4
10-3
Lunar Laser Ranging (2007)
(4×10-5)
Recent SGs
(~10-5)

9. Searching for gravitational waves
Excitation of Earth’s normal modes (Weber1960 PRL)
Upper limits placed in 1960s. (Forward et al 1961 Nature, Weber 1968 PRL)
Low frequency (~0.3 mHz), c.f. ground-based gravitational-wave detectors ( Hz).
T. Sato

10. Searching for scalar gravitational waves
Excitation of Earth’s normal modes
(Dicke et al 1964)
T. Sato

11. Summary of geophysical tests
Searched for signals
Expected phenomena on the Earth
Periods of the signals
Preferred-frame effects
Preferred-location effects
Anomalous tides
12 hours
Gravitational waves
Scalar gravitational waves
Excitation of 0S2 mode
Excitation of 0S0 mode
53.9 mins
20.5 mins
Violation of the universality of free-fall
Composition-dependent dilatonic waves
Translational motions of the inner core
Excitation of translational motions of the inner core
~24 hours
4-6 hours
Long periods:
SGs are most suitable.

12. Future works Improving noise reduction methods
Identification of environmental noise
Data analyses to extract weak signals (Rosat et al J. of Geophys. 2007)
Figuring out the optimum scheme of global observations
e.g. coincidence measurements

13. Improving the Earth model
Neutrino oscillation tomography of Earth’s interior (Winter PRD(2005))
Detection of the antinutrino from the Earth (KamLAND, Nature 2005)
High pressure and high temperature experiments to determine the core’s viscosity
(Mineev and Funtikov 2004).
Coincidence measurements with a laser strain meter and a SG at the Kamioka Observatory (S. Takemoto et al 2004).
others

14. Conclusions
We can improve the upper limits on the preferred frame and location effects, comparable with LLR.
Searching for gravitational waves and scalar gravitational waves at low frequencies: ~0.1 mHz.
The Earth model could be improved significantly in the near future.