Abhishek Basak, Jitesh R. Bhatt
We study the first order perturbations in a non-minimally coupled scalar field theory in the Jordan frame. It is shown by comparing the expression for the spectral index $n_{\mr}$ with the observed value that the non-minimal coupling constant $\xi$ can have an upper bound. The bound on $\xi$ is generic as it is obtained without assuming any specific form of potential. Source of this bound is due to the presence of $\lambda_{1}=frac{\dot f}{Hf}$ term in the Friedman equation, where $f$ signifies the non-minimal coupling term. From the Einstein's equation it is shown that the comoving curvature perturbation depends on parameter $\lambda_1$ and it would evolve on the super horizon scales unless the bound on $\xi$ is imposed.
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http://arxiv.org/abs/1208.3298
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