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Spectator-field-triggered phase transition during inflation and its anisotropic gravitational wave signals

Yunjia Bao1,* and Keisuke Harigaya1,2,†

  • *Contact author: yunjia.bao@uchicago.edu
  • †Contact author: kharigaya@uchicago.edu
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Phys. Rev. D 114, 055008 – Published 15 September, 2026

DOI: https://doi.org/10.1103/z1ws-kb9z

Abstract

We propose a general framework in which a phase transition is triggered during cosmic inflation by the slow-roll dynamics of a spectator field. The topological defects formed at the transition are inflated outside the horizon, reenter it after inflation, and can subsequently generate characteristic gravitational wave (GW) signals. Quantum fluctuations of the spectator field modulate the timing of the transition, imprinting large-scale anisotropies in the resulting GW background. As an explicit realization, the spectator field may be identified with the Higgs field in a supersymmetric Standard Model. More generally, our framework applies to a wide class of spectator-modulated phenomena, providing a generic mechanism for producing anisotropic GW signals.

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Phys. Rev. D 114, 055008– Published 15 September, 2026
  • Received 14 January 2026
  • Accepted 13 August 2026
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