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Large-scale structure power spectrum from scalar-tensor gravity

This work deals with the computation of the power spectrum of large-scale structure using the dynamical system approach for a multi-fluid universe in scalar-tensor theory of gravity. We use the $1+3$ covariant approach to obtain evolution equations and study the behavior of the matter power spectrum of perturbation equations. The study is based on the equivalence between $f(R)$ theory of gravity and scalar-tensor theory of gravity. We find that, for power-law $(R^{n})$ models, with $1<n<1.3$, we have the power spectrum evolving above general relativistic scale-invariant line. For $n\geq 1.3$, the power spectrum starts with constant amplitude then it experiences oscillations and eventually saturates at finite amplitude. Such behavior is consistent with other observations in the literature. The result supports the ongoing investigations of the equivalence between $f(R)$ and scalar-tensor theory at linear order.