Weak-field limit of Kaluza-Klein models with spherical compactification: experimental constraints

We investigate the classical gravitational tests for the six-dimensional Kaluza-Klein model with spherical (of a radius $a$) compactification of the internal space. The model contains also a bare multidimensional cosmological constant $Λ_6$. The matter, which corresponds to this ansatz, can be simulated by a perfect fluid with the vacuum equation of state in the external space and an arbitrary equation of state with the parameter $ω_1$ in the internal space. For example, $ω_1=1$ and $ω_1=2$ correspond to the monopole two-forms and the Casimir effect, respectively. In the particular case $Λ_6=0$, the parameter $ω_1$ is also absent: $ω_1=0$. In the weak-field approximation, we perturb the background ansatz by a point-like mass. We demonstrate that in the case $ω_1>0$ the perturbed metric coefficients have the Yukawa type corrections with respect to the usual Newtonian gravitational potential. The inverse square law experiments restrict the parameters of the model: $a/\sqrt{ω_1}\lesssim 6\times10^{-3}\ {cm}$. Therefore, in the Solar system the parameterized post-Newtonian parameter $γ$ is equal to 1 with very high accuracy. Thus, our model satisfies the gravitational experiments (the deflection of light and the time delay of radar echoes) at the same level of accuracy as General Relativity. We demonstrate also that our background matter provides the stable compactification of the internal space in the case $ω_1>0$. However, if $ω_1=0$, then the parameterized post-Newtonian parameter $γ=1/3$, which strongly contradicts the observations.

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