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Suppression of scalar perturbations due to a heavy axion

Kai-Ge Zhang1,2,*, Jian-Feng He3,4,†, Chengjie Fu5,‡, and Zong-Kuan Guo3,4,6,§

  • *Contact author: zhangkaige21@mails.ucas.ac.cn
  • †Contact author: hejianfeng@itp.ac.cn
  • ‡Contact author: fucj@ahnu.edu.cn
  • §Contact author: guozk@itp.ac.cn
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Phys. Rev. D 113, 023531 – Published 21 January, 2026

DOI: https://doi.org/10.1103/4wtv-xdwj

Abstract

A fast-rolling axion can transfer its kinetic energy to gauge fields via the Chern-Simons coupling, leading to copious production of gauge quanta during inflation. The amplified gauge fields act as a source for both scalar and tensor perturbations. In this work, we propose a mechanism for suppressing scalar perturbations while sourcing strong tensor perturbations. We present an implementation of such a mechanism, demonstrating that sourced tensor perturbations are expected to be detected by upcoming next-generation cosmic microwave background experiments.

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Phys. Rev. D 113, 023531– Published 21 January, 2026
  • Received 9 October 2025
  • Accepted 5 January 2026
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