Large field inflation from D-branes

TL;DR

The paper addresses realizing large-field inflation within string theory by employing F-term axion monodromy driven by D-branes, to separate the inflaton potential source from moduli stabilisation. The authors construct a Type IIA setup with D6-branes yielding a superpotential $W_{ m inf} = \Phi T$ and a warped geometry to suppress the inflaton mass relative to other moduli, enabling an effectively single-field inflation along the axionic direction $b=\text{Re} T$. They perform a two-step moduli stabilisation and include Planck-suppressed corrections from DBI that flatten the quadratic potential to $V = \gamma\left(\sqrt{1+\delta \left(\frac{\phi_b}{M_{\rm pl}}\right)^2}-1\right) M_{\rm pl}^4$, allowing compatibility with Planck data across a range of $(\delta,\gamma)$. The results illustrate a viable mechanism to realize large-field inflation in string theory with controlled backreaction and concrete phenomenological predictions, including a $ abla n_s$ and $r$ that depend on the flattening parameter $\delta$.

Abstract

We propose new large field inflation scenarios built on the framework of F-term axion monodromy. Our setup is based on string compactifications where D-branes create potentials for closed string axions via F-terms. Because the source of the axion potential is different from the standard sources of moduli stabilisation, it is possible to lower the inflaton mass as compared to other massive scalars. We discuss a particular class of models based on type IIA flux compactifications with D6-branes. In the small field regime they describe supergravity models of quadratic chaotic inflation with a stabiliser field. In the large field regime the inflaton potential displays a flattening effect due to Planck suppressed corrections, allowing to easily fit the cosmological parameters of the model within current experimental bounds.

Figures (3)

• Figure 1: Tensor-to-scalar ratio obtained in terms of $\delta$
• Figure 2: Spectral index in terms of $\delta$
• Figure 3: Primordial tilt $n_{s}$ vs $r$ given by Planck Collaboration. The yellow area shows the region covered by $\delta \sim 10^{-1} - 10^{-3}$.