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Lorentz invariance (LI) is the founding postulate of Einstein's 1905 theory of relativity, and therefore at the heart of all accepted theories of physics. It characterizes the invariance of the laws of physics in inertial frames under changes of velocity or orientation. This central role, and indications from unification theories (Kostelecky, 1989) hinting toward a possible LI violation, have motivated...
This article describes the work performed at BNM-SYRTE (Observatoire de Paris) in the past few years, toward the improvement and the use of microwave frequency standards using laser-cooled atoms. First, recent improvements of the 133 Cs and 87 Rb atomic fountains are described. An important advance is the achievement of a fractional frequency instability of 1.6×10−14τ−1/2 where τ is...
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