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Recently I've read some papers on inflation and slow roll approximation. As we all know, inflation parameters are constrained by recent Bicep2/Keck and Planck data, which gives values of scalar-to-tensor ratio as well as spectral index of primordial curvature perturbations - i have simple or even naive question - since scalar to tensor ratio is constrained (for example 2014 data) as: $r<0.10$ does it mean that this ratio can be negative?

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Tensor-to-scalar ratio is defined as the ratio of the amplitude of tensor perturbations (primordial gravitational waves) to the amplitude of scalar perturbations, and as such cannot be negative.

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