Natural Inflation with Natural Trans-Planckian Axion Decay Constant from Anomalous $U(1)_X$

TL;DR

This paper presents a string-inspired supergravity model where an axionic component of a Kähler modulus drives natural inflation with a trans-Planckian decay constant, aligning with BICEP2 data.

Contribution

It introduces a novel mechanism for achieving a trans-Planckian axion decay constant via gauged shift symmetry and modulus stabilization in string-inspired supergravity.

Findings

Realizes natural inflation with trans-Planckian decay constant

Separates masses of modulus components at different scales

Aligns inflationary predictions with BICEP2 observations

Abstract

We propose a natural inflation model driven by an imaginary or axionic component of a K\"ahler modulus in string-inspired supergravity. The shift symmetry of the axion is gauged under an anomalous $U(1)_X$ symmetry, which leads to a modulus-dependent Fayet-Iliopoulos (FI) term. The matter fields are stabilized by F-terms, and the real component of the modulus is stabilized by the $U(1)_X$ D-term, while its axion remains light. Therefore, the masses of real and imaginary components of the modulus are separated at different scales. The scalar potential for natural inflation is realized by the superpotential from the non-perturbative effects. The trans-Planckian axion decay constant, which is needed to fit with BICEP2 observations, can be obtained naturally in this model.