Retrieving "Spacetime Metric" from the archives

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1. Cosmology (inflationary Models)

   Linked via "spacetime metric"

   Tensor Perturbations
   Tensor modes represent quantum fluctuations in the spacetime metric itself, manifesting as a background of primordial gravitational waves. The strength of this background is parameterized by the tensor-to-scalar ratio), $r \equiv PT(k) / PS(k)$. Inflationary theory strongly predicts that $r$ should be non-zero, though current observational bounds from experiments like BICEP/Keck have significantly constrained the parameter space, forcing m…