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

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

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

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)

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

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.

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.

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)

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 (10-1000Hz). T. Sato

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

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.

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

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

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.