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We compute the PPN parameters $\gamma$ and $\beta$ for general scalar-tensortheories in the Einstein frame, which we compare to the existing PPNformulation in the Jordan frame for alternative theories of gravity. Thiscomputation is important for scalar-tensor theories that are expressed in theEinstein frame, such as chameleon and symmetron theories, which can incorporatehiding mechanisms that predict environment-dependent PPN parameters. Weintroduce a general formalism for scalar-tensor theories and constrain it usingthe limit on $\gamma$ given by the Cassini experiment. In particular we discussmassive Brans-Dicke scalar fields for extended sources. Next, using a recentlyproposed Earth satellite experiment, in which atomic clocks are used forspacecraft tracking, we compute the observable perturbations in the redshiftinduced by PPN parameters deviating from their general relativistic values. Ourestimates suggest that $|\gamma - 1| \sim |\beta -1| \sim 10^{-6}$ may bedetectable by a satellite that carries a clock with fractional frequencyuncertainty $\Delta f/f \sim 10^{-16}$ in an eccentric orbit around the Earth.Such space experiments are within reach of existing atomic clock technology. Wediscuss further the requirements necessary for such a mission to detectdeviations from Einstein relativity.

Testing scalar-tensor theories and PPN parameters in Earth orbit