Detecting relic gravitational waves in the CMB: Optimal parameters and their constraints

Understand

The prospect of detecting relic gravitational waves (RGWs), through their imprint in the cosmic microwave background radiation, provides an excellent opportunity to study the very early Universe.

• In simplest viable theoretical models the RGW background is characterized by two parameters, the tensor-to-scalar ratio $r$ and the tensor spectral index $n_t$.
• In this paper, we analyze the potential joint constraints on these two parameters, $r$ and $n_t$, using the data from the upcoming cosmic microwave background radiation experiments.
• Introducing the notion of the best pivot multipole $\ell_t^*$, we find that at this pivot multipole the parameters $r$ and $n_t$ are uncorrelated, and have the smallest variances.