The Powers of Monodromy

TL;DR

This paper explores monodromy effects in string theory axions, presenting new inflation models with flattened potentials, and predicts observable tensor-to-scalar ratios based on specific compactification scenarios.

Contribution

It introduces novel classes of monodromy inflation models with effective potential flattening, derived from string compactifications involving fluxes and moduli stabilization.

Findings

Models with various power-law potentials and specific tensor-to-scalar ratios.

Demonstrates potential flattening effects due to inflaton-moduli interactions.

Provides string theory realizations of large-field inflation scenarios.

Abstract

Flux couplings to string theory axions yield super-Planckian field ranges along which the axion potential energy grows. At the same time, other aspects of the physics remain essentially unchanged along these large displacements, respecting a discrete shift symmetry with a sub-Planckian period. After a general overview of this monodromy effect and its application to large-field inflation, we present new classes of specific models of monodromy inflation, with monomial potentials $\mu^{4-p}\phi^p$. A key simplification in these models is that the inflaton potential energy plays a leading role in moduli stabilization during inflation. The resulting inflaton-dependent shifts in the moduli fields lead to an effective flattening of the inflaton potential, i.e. a reduction of the exponent from a fiducial value $p_0$ to $p<p_0$. We focus on examples arising in compactifications of type IIB string theory on products of tori or Riemann surfaces, where the inflaton descends from the NS-NS two-form potential $B_2$, with monodromy induced by a coupling to the R-R field strength $F_1$. In this setting we exhibit models with $p=2/3,4/3,2,$ and $3$, corresponding to predictions for the tensor-to-scalar ratio of $r\approx 0.04, 0.09, 0.13,$ and $0.2$, respectively. Using mirror symmetry, we also motivate a second class of examples with the role of the axions played by the real parts of complex structure moduli, with fluxes inducing monodromy.