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

Comments: 33 pages, 12 figures, revised version, additional text and references, main results unchanged