Natural Chaotic Inflation and UV Sensitivity

TL;DR

The work investigates UV sensitivity in large-field chaotic inflation using a benchmark axion-4-form (natural chaotic inflation) framework, motivated by potential BICEP2 signals and a GUT-scale inflation energy $V \sim M_{GUT}^4$. It shows that a tree-level quadratic potential $V=\frac{1}{2}\mu^2 \phi^2$ can be realized with small corrections controlled by a UV scale $M_{uv}$ near $M_{GUT}$ in high-scale string models. Corrections from UV physics, including higher-dimension terms $\delta V \sim V_{tree}(V_{tree}/M_{uv}^4)^n$ and moduli couplings, can modify $P_S$, $P_T$, and $r$ notably, especially when $M_{uv}$ is close to $M_{GUT}$, potentially leaving observable imprints. The work highlights that large-field inflation in string theory can be testable via precision CMB measurements, but requires careful moduli stabilization and sequestering, with possible early-universe signatures from nonperturbative transitions.

Abstract

If the recent measurement of B-mode polarization by BICEP2 is due to primordial gravitational waves, it implies that inflation was driven by energy densities at the GUT scale $M_{GUT} \sim 2\times 10^{16} GeV$. This favors single-field chaotic inflation models. These models require transplanckian excursions of the inflaton, forcing one to address the UV completion of the theory. We use a benchmark 4d effective field theory of axion-4-form inflation to argue that inflation driven by a quadratic potential (with small corrections) is well motivated in the context of high-scale string theory models; that it presents an interesting incitement for string model building; and the dynamics of the UV completion can have observable consequences.

Figures (1)

• Figure 1: Energies as a function of $\phi$, for the potential $V = \frac{1}{2} (\mu \phi + q)^2$. The picture repeats itself each time one shifts $\phi \to \phi + e^2/\mu \equiv \phi + f$.