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Axion superradiance in dipole magnetic fields of pulsars

Topi Sirkiä*, Matti Heikinheimo†, and Kimmo Tuominen‡

  • *Contact author: topi.sirkia@helsinki.fi
  • †Contact author: matti.heikinheimo@helsinki.fi
  • ‡Contact author: kimmo.i.tuominen@helsinki.fi
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Phys. Rev. D 111, 115030 – Published 25 June, 2025

DOI: https://doi.org/10.1103/gs6h-xlk8

Abstract

We consider constraints on the axion-photon coupling by superradiance due to a plasma instability in the magnetospheres of millisecond pulsars. We compute the growth rate of a superradiant axion cloud in a dipole magnetic field, and give a semianalytical formula for the superradiance rate for the lowest state. By requiring the associated instability time to be longer than the characteristic age of the supermassive black-widow millisecond pulsar PSR J0952-0607, we examine the pulsar-timing array constraints on axions of mass ∼10−12  eV. We find that competitive axion bounds from plasma instabilities are unlikely unless a new high spin pulsar is discovered.

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Phys. Rev. D 111, 115030– Published 25 June, 2025
  • Received 11 April 2025
  • Accepted 4 June 2025
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