Canonical and Non-canonical Inflation in the light of the recent BICEP/Keck results (2202.03467v2)

Abstract: We discuss implications of the latest BICEP/Keck data release for inflationary models, with particular emphasis on scalar fields with non-canonical Lagrangians of the type ${\cal L} = X^\alpha - V(\phi)$. The observational upper bound on the tensor-to-scalar ratio, $r \leq 0.036$, implies that the whole family of monomial power law potentials $V(\phi) \sim \phi^p$ are now ruled out in the canonical framework at $95\%$ confidence, which includes the simplest classic inflationary potentials such as $\frac{1}{2}m^2 \phi^2$ and $\lambda \phi^4$. Instead, current observations strongly favour asymptotically flat plateau potentials. However, working in the non-canonical framework, we demonstrate that monomial potentials, as well as the Higgs potential with its Standard Model self-coupling, can easily be accommodated by current CMB data. We find striking similarities between the $\lbrace n_{S}, r\rbrace$ flow lines of monomial potentials in the non-canonical framework and the T-model $\alpha$-attractors in the canonical framework. Significantly, $V(\phi)$ can originate from Planck scale initial values $V(\phi) \simeq m_p^4$ in non-canonical models while in plateau-like canonical inflation the initial value of the potential is strongly suppressed $V{\rm plat}(\phi) \leq 10^{-10} m_p^4$. This has bearing on the issue of initial conditions for inflation and allows for the equipartition of the kinetic and potential terms in non-canonical models.