Starobinsky-Type Inflation from $α'$-Corrections

TL;DR

This work demonstrates how Starobinsky-like inflation can be realized within the Large Volume Scenario of type IIB string compactifications by leveraging α'^3 higher-derivative corrections to generate a plateau for a fibre modulus, with string-loop corrections providing the necessary exit. The authors show two viable regimes—inflation to the left and to the right—each yielding a nearly identical n_s ~ 0.97 but differing in the tensor-to-scalar ratio, r ≈ (2–7)×10^−3, and requiring only moderate tuning of underlying microscopic parameters. A careful mass hierarchy among moduli ensures single-field dynamics, and higher-order corrections introduce small, testable running and a percent-level power suppression at large scales. Overall, the paper provides a concrete, UV-complete string-theoretic realization of large-field plateau inflation with Planck-compatible predictions and identifiable observational distinctions between the two branches.

Abstract

Working in the Large Volume Scenario (LVS) of IIB Calabi-Yau flux compactifications, we construct inflationary models from recently computed higher derivative $(α')^3$-corrections. Inflation is driven by a Kaehler modulus whose potential arises from the aforementioned corrections, while we use the inclusion of string loop effects just to ensure the existence of a graceful exit when necessary. The effective inflaton potential takes a Starobinsky-type form $V=V_0(1-e^{-νφ})^2$, where we obtain one set-up with $ν=-1/\sqrt{3}$ and one with $ν=2/\sqrt{3}$ corresponding to inflation occurring for increasing or decreasing $φ$ respectively. The inflationary observables are thus in perfect agreement with PLANCK, while the two scenarios remain observationally distinguishable via slightly varying predictions for the tensor-to-scalar ratio $r$. Both set-ups yield $r\simeq (2\ldots 7)\,\times 10^{-3}$. They hence realise inflation with moderately large fields $\left(Δφ\sim 6\thinspace M_{Pl}\right)$ without saturating the Lyth bound. Control over higher corrections relies in part on tuning underlying microscopic parameters, and in part on intrinsic suppressions. The intrinsic part of control arises as a leftover from an approximate effective shift symmetry at parametrically large volume.

Figures (2)

• Figure 1: Scalar potential of Eq. \ref{['firstAttempt']} (in units of $g_s^2 \left(\frac{W_0}{\mathcal{V}}\right)^4$) for different choices of the topological integers $\Pi_1$ and $\Pi_2$.
• Figure 2: Left:The canonical inflaton potential for $\mathcal{C}_1>0$ and arbitrary $\mathcal{C}_2$. String loops ensure that the potential is bounded from below while inflation is driven by the $\mathcal{C}_1$-term of $V_{(1)}$. If $\mathcal{C}_2>0$ there can be observed running of the spectral index $n_s$.Right:The inflaton rolls to the right. Inflation is driven by the $\mathcal{C}_2$-term of $V_{(1)}$.