Moduli Stabilization and Inflationary Cosmology with Poly-Instantons in Type IIB Orientifolds

TL;DR

This work develops a concrete Type IIB orientifold setup within the LARGE Volume Scenario where poly-instanton corrections lift a flat Wilson-line divisor modulus, allowing it to act as the inflaton. By comparing a minimal scheme to a racetrack extension, the authors achieve moduli stabilization with a clear mass hierarchy and identify the Wilson-line modulus as a viable slow-rolling inflaton. Their four benchmark models yield robust inflationary predictions: a high scale (∼10^14 GeV), negligible tensor modes (r ∼ 10^-9), and a spectral index near current observations (n_S ≈ 0.967–0.969), with reheating temperatures around 10^6–10^7 GeV. The results illustrate how subleading non-perturbative effects in LVS can realize controlled, closed-string inflation with testable cosmological implications, while highlighting the need for more complete visible-sector embeddings in future work.

Abstract

Equipped with concrete examples of Type IIB orientifolds featuring poly-instanton corrections to the superpotential, the effects on moduli stabilization and inflationary cosmology are analyzed. Working in the framework of the LARGE volume scenario, the Kaehler modulus related to the size of the four-cycle supporting the poly-instanton contributes sub-dominantly to the scalar potential. It is shown that this Kaehler modulus gets stabilized and, by displacing it from its minimum, can play the role of an inflaton. Subsequent cosmological implications are discussed and compared to experimental data.

Figures (7)

• Figure 1: The scalar potential $V({\cal V},\tau_s)$ (multiplied by $10^{7}$) as a function of ${\cal V}$ and $\tau_s$ in the absence of poly-instanton effects. The model dependent parameters have been chosen to be $\chi({\cal M}) = -136$, $\xi_b = \frac{1}{36}$, $\xi_s = \xi_{sw} =\frac{1}{6\sqrt2}$, $a_s = \frac{2\pi}{4}$, $A_s =8$, $g_s= 0.12$, $W_0 = -5$. The respective minimum values for the moduli are $\overline\rho_s=0$, $\overline\tau_s = 5.44$, $\overline{\cal V} = 1086$.
• Figure 2: The scalar potential $V({\cal V},\tau_s)$ (multiplied by $10^{7}$) vs ${\cal V}$ and $\tau_s$ for benchmark model ${\cal B}_1$ in the absence of poly-instanton effects.
• Figure 3: The effective scalar potential $V(\tau_w)$ vs $\tau_w$ at stabilized value of the heavier moduli $\overline{\cal V}, \overline\tau_s$ for benchmark model ${\cal B}_1$.
• Figure 4: The inflationary potential $V(\hat{\chi})$ vs the inflaton-shift $\hat{\chi}$ for the benchmark model ${\cal B}_1$ while keeping the heavier moduli at their respective minima $\overline{\cal V},~\overline\tau_s$. The flat region of the potential is the relevant inflationary region where slow-roll conditions are satisfied.
• Figure 5: For benchmark model ${\cal B}_1$, the two slow-roll parameters $\epsilon(\hat{\chi})$ and $\eta(\hat{\chi})$ are displayed for inflaton shift $\hat{\chi}$ focussing on locating the slow-roll regime where $\epsilon \ll |\eta| \ll 1$.