https://doi.org/10.1140/epjc/s10052-024-12969-2
Regular Article - Theoretical Physics
On the (un)testability of the general free scalar–tensor gravity for the Solar System tests
1
Purple Mountain Observatory, Chinese Academy of Sciences, 210023, Nanjing, China
2
School of Astronomy and Space Science, University of Science and Technology of China, 230026, Hefei, China
Received:
28
April
2024
Accepted:
26
May
2024
Published online:
18
June
2024
Recently, Zhang et al. [Eur. Phys. J. C 84, 381, https://doi.org/10.1140/epjc/s10052-024-12723-8 (2024)] constrained the Yukawa correction in the general free scalar–tensor gravity by borrowing the measured values of the parametrized post-Newtonian (PPN) parameters 
and 
in the Solar System tests. They firstly defined two PPN parameters 
and 
in the gravity, which depend on the radial distance r and include the Yukawa-type parameters. Then, by comparing between the experiments’ results of two PPN parameters and their and , the authors claimed that they gave the tightest bound on the gravity by the Cassini tracking experiment. However, we find their approach is not rigorous. In this paper, corresponding astronomical experiments have been physically modelled by considering the lightlike and the timelike geodesics in the general free scalar–tensor gravity. Contrary to the wrong results in Zhang et al.’s work, it is shown that the Cassini tracking experiment is insensitive to the general free scaler–tensor gravity. Furthermore, we also find that the time delay and the light deflection are all independent of the gravity. Due to an additional Yukawa-type advance in the periastron shift, we derive very much improved bounds on the Yukawa-type parameters of this gravity.
© The Author(s) 2024
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