Canonical and Non-canonical Inflation in the light of the recent BICEP/Keck results

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 ${\cal L} = X^α- V(ϕ)$. The observational upper bound on the tensor-to-scalar ratio, $r \leq 0.036$, implies that the whole family of monomial power law potentials $V(ϕ) \sim ϕ^p$ are now ruled out in the canonical framework at $95\%$ confidence, which includes the simplest classic inflationary potentials such as $\frac{1}{2}m^2 ϕ^2$ and $λϕ^4$. 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 $α$-attractors in the canonical framework. Significantly, $V(ϕ)$ can originate from Planck scale initial values $V(ϕ) \simeq m_p^4$ in non-canonical models while in plateau-like canonical inflation the initial value of the potential is strongly suppressed $V_{\rm plat}(ϕ) \leq 10^{-10} m_p^4$. 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.