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  • Open Access

Primordial power spectrum and bispectrum from lattice simulations of axion-U(1) inflation

Drew Jamieson1,*, Angelo Caravano2,†, and Eiichiro Komatsu1,3,4

  • *Contact author: jamieson@mpa-garching.mpg.de
  • †Contact author: caravano@iap.fr
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Phys. Rev. D 112, 103531 – Published 18 November, 2025

DOI: https://doi.org/10.1103/3zml-71jd

Abstract

We present primordial non-Gaussianity predictions from a new high-precision code for simulating axion-U(1) inflation on a discrete lattice. We measure the primordial scalar curvature power spectrum and bispectrum from our simulations, determining their dependence on both scale and axion-gauge coupling strength. Both the gauge-sourced power spectrum and the bispectrum exhibit a strong blue tilt due to our choice of an α-attractor inflaton potential. We provide fitting functions for the power spectrum and bispectrum that accurately reproduce these statistics across a wide range of scales and coupling strengths. While our fitting function for the bispectrum has a separable form, results from high-resolution simulations demonstrate that the full shape is not separable. Thus, our simulations generate realizations of primordial curvature perturbations with nontrivial correlators that cannot be generated using standard techniques for primordial non-Gaussianity. We derive bounds on the axion-gauge coupling strength based on the bispectrum constraints from the cosmic microwave background, demonstrating a new method for constraining inflationary primordial non-Gaussianity by simulating the nonlinear dynamics.

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Phys. Rev. D 112, 103531– Published 18 November, 2025
  • Received 18 August 2025
  • Accepted 13 October 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

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