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Testing local position invariance with four Cesium fountain primary frequency standards and four NIST Hydrogen masers



Neil Ashby, Thomas P. Heavner, Steven R. Jefferts, Thomas E. Parker, A Radnaev, Y Dudin


Local Position Invariance (LPI), together with Local Lorentz Invariance (LLI) and the Weak Equivalence Principle (WEP) form the foundation of the General Theory of Relativity. LPI implies that if atomic clocks of different structures are placed together and syntonized, they will remain syntonized while they move through a variable gravitational potential. In this paper we compare four active Hydrogen masers located at NIST with Cesium fountain primary frequency standards from NIST, PTB, LNE-SYRTE, and INRIM. For the primary standard at NIST, seven years? worth of observations are available, while comparisons with fountains at PTB, LNE-SYRTE, and INRIM have been reliably conducted for about four, two, and two years, respectively. During these observations the sun?s gravitational potential changes due to the earth?s orbital eccentricity, with an amplitude given by{Δ}Φ /c2 {approximately equal} GM e/(c2a){approximately equal} 1.66?10−10, where e is earth?s orbital eccentricity and a denotes the earth?s semimajor axis. The Cs-H Maser comparisons show no correlation with variations in the solar gravitational potential, within an uncertainty that is about 30 times smaller than the previous most sensitive comparisons.
Physical Review Letters


atomic clock, fundamental contstants, general relativity, LPI


Ashby, N. , Heavner, T. , Jefferts, S. , Parker, T. , Radnaev, A. and Dudin, Y. (2007), Testing local position invariance with four Cesium fountain primary frequency standards and four NIST Hydrogen masers, Physical Review Letters, [online], (Accessed July 21, 2024)


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Created February 16, 2007, Updated February 19, 2017