Non-Gaussianity in rapid-turn multi-field inflation

TL;DR

This paper demonstrates that multi-field inflation with rapid turns can produce significant non-Gaussianity, especially large local bispectrum signals, which are crucial for interpreting future cosmological observations.

Contribution

It introduces a new analytical formula for the bispectrum in multi-field rapid-turn inflation, accounting for non-zero cross-correlations and diverse shapes.

Findings

Rapid-turn inflation can generate large local non-Gaussianity.

The derived formula captures multiple contributions to the bispectrum.

Explicit model confirms potential for $f_{NL}^{loc} o O(1)$.

Abstract

We show that theories of inflation with multiple, rapidly turning fields can generate large amounts of non-Gaussianity. We consider a general theory with two fields, an arbitrary field-space metric, and a potential that supports sustained, rapidly turning field trajectories. Our analysis accounts for non-zero field cross-correlation and does not fix the power spectra of curvature and isocurvature perturbations to be equal at horizon crossing. Using the $\delta N$ formalism, we derive a novel, analytical formula for bispectrum generated from multi-field mixing on super-horizon scales. Rapid-turn inflation can produce a bispectrum with several potentially large contributions that are not necessarily of the local shape. We exemplify the applicability of our formula with a fully explicit model and show that the new contributions indeed can generate a large amplitude of local non-Gaussianity, $f_{\rm NL}^{\rm loc}\sim {\cal O}(1)$. These results will be important when interpreting the outcomes of future observations.