# Weak field limit of higher dimensional massive Brans-Dicke gravity: Observational constraints

## TL;DR

This paper investigates higher-dimensional massive Brans-Dicke gravity, deriving solutions for perturbations, and constrains the model parameters using observational tests, showing compatibility with gravity experiments for specific parameter ranges.

## Contribution

It provides exact solutions for perturbations in higher-dimensional massive Brans-Dicke theory and derives observational constraints on model parameters, including scalar field mass and internal space equation-of-state.

## Key findings

- Model does not contradict PPN parameter gamma constraints.
- Scalar field is not ghost for certain parameter values.
- Yukawa correction imposes lower bound on scalar mass.

## Abstract

We consider higher-dimensional massive Brans-Dicke theory with Ricci-flat internal space. The background model is perturbed by a massive gravitating source which is pressureless in the external (our space) but has an arbitrary equation-of-state parameter $\Omega$ in the internal space. We obtain the exact solution of the system of linearized equations for the perturbations of the metric coefficients and scalar field. For a massless scalar field, relying on the fine-tuning between the Brans-Dicke parameter $\omega$ and $\Omega$, we demonstrate that (i) the model does not contradict gravitational tests relevant to the parameterized post-Newtonian parameter $\gamma$, and (ii) the scalar field is not ghost in the case of nonzero $|\Omega|\sim O(1)$ along with the natural value $|\omega|\sim O(1)$. In the general case of a massive scalar field, the metric coefficients acquire the Yukawa correction terms, where the Yukawa mass scale $m$ is defined by the mass of the scalar field. For the natural value $\omega\sim O(1)$, the inverse-square-law experiments impose the following restriction on the lower bound of the mass: $m\gtrsim 10^{-11}\,$GeV. The experimental constraints on $\gamma$ requires that $\Omega$ must be extremely close to $-1/2$.