Abstract
We study string inspired two-field models of large-field inflation based on axion monodromy in the presence of an interacting heavier modulus. This class of models has enough structure to approximate at least part of the backreaction effects known in full string theory, such as kinetic mixing with the axion, and flattening of the scalar potential. Yet, it is simple enough to fully describe the structure of higher-point curvature perturbation interactions driven by the adjusting modulus backreaction dynamics. We find that the presence of the heavy modulus can be described via two equivalent effective field theories, both of which can incorporate reductions of the speed of sound. Hence, the presence of heavier moduli in axion monodromy inflation constructions will necessarily generate some amount of non-Gaussianity accompanied by changes to $n_s$ and $r$ beyond what results from just from the well known adiabatic flattening backreaction.
Highlights
The scenario of cosmological inflation has become the standard paradigm for generating the initial conditions of the hot FRW “big bang” epoch starting with reheating and sourcing the seeds of structure formation from a nearly scale-invariant spectrum of phase-coherent quantum curvature perturbations
We study string inspired two-field models of large-field inflation based on axion monodromy in the presence of an interacting heavier modulus
We find that depending on the relative importance of kinetic coupling vs coupling in the potential, the simple single-field predictions of axion monodromy inflation ns − 1 1⁄4 −ðp þ 2Þ=ð2NeÞ and r 1⁄4 4p=Ne in terms of the asymptotic flattened large-field potential V ∼ φp can be significantly changed
Summary
The scenario of cosmological inflation has become the standard paradigm for generating the initial conditions of the hot FRW “big bang” epoch starting with reheating and sourcing the seeds of structure formation from a nearly scale-invariant spectrum of phase-coherent quantum curvature perturbations. Higher-point interactions of the inflationary perturbations seem to arise in string theory models of inflation mostly in two ways: either non-Gaussianity originates from the direct fundamental presence of higher-derivative kinetic terms such as in DBI inflation [6], or it is due to the presence of more or less heavy “spectator” moduli fields backreacting to the dynamics of the inflaton scalar (which may be a modulus itself, or alternatively a stringy axion arising from higherdimensional p-form gauge fields).
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