The UV Sensitivity of Axion Monodromy Inflation

TL;DR

This paper shows that heavy fields in axion monodromy inflation can be excited during inflation, producing detectable signals in the primordial bispectrum that reveal high-energy physics beyond the Hubble scale.

Contribution

It introduces a string-inspired two-field model demonstrating how oscillatory modulations excite heavy fields, challenging single-field assumptions and producing observable collider signals.

Findings

Heavy moduli can be excited during inflation due to oscillatory potential modulations.

These excitations produce large signals in the primordial bispectrum.

The mechanism bypasses Boltzmann suppression, making high-energy physics observable.

Abstract

We revisit axion monodromy inflation in the context of UV-inspired models and point out that its cosmological observables are sensitive to heavy fields with masses far above the Hubble scale, such as the moduli of flux compactifications. By studying a string-inspired two-field extension of axion monodromy with a small turning rate, we reveal that the oscillatory modulation of the axion potential leads to continuous excitation of heavy fields during inflation when the modulation frequency exceeds the field masses. This finding challenges the conventional single-field description, heavy moduli cannot be simply integrated out. Using a full bootstrap analysis, we demonstrate that this mechanism produces cosmological collider signals that bypass the usual Boltzmann suppression for heavy masses. Specifically, we identify detectably large signatures of heavy moduli in the primordial bispectrum, offering a promising avenue for probing high-energy physics through cosmological observations.