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Pulse and Polarization Structures in Axion-Converted X-Rays from Pulsars.

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  • 1Brown University, Department of Physics and Brown Theoretical Physics Center, Providence, Rhode Island 02912, USA.

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|December 19, 2025
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Pulsation patterns in neutron star X-rays may reveal axions, feebly coupled particles. Analyzing X-ray Dim Isolated Neutron Star RX J1856.6-3754 shows axion signals are possible but require reduced uncertainties for definitive conclusions.

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Area of Science:

  • Astrophysics
  • Particle Physics

Background:

  • Neutron stars (NSs) possess extreme magnetic fields and dense cores, making them potential sources for axion production.
  • Axions are hypothetical feebly coupled particles, and their detection could signify new physics beyond the Standard Model.

Purpose of the Study:

  • To investigate the potential of X-ray pulsation structures from NSs as probes for axions.
  • To develop analytical formalisms for analyzing axion-induced X-ray intensity and polarization pulsations.

Main Methods:

  • Development of new analytical formalisms for pulsation-polarization structure analysis in axion scenarios.
  • Application of the formalism to X-ray Dim Isolated Neutron Star RX J1856.6-3754, analyzing its hard X-ray excess.
  • Updated fitting of intensity and pulsation data to assess axion compatibility.

Main Results:

  • The axion explanation for the hard X-ray excess in RX J1856.6-3754 is compatible with available intensity and pulsation data.
  • Incorporating pulsation data shifts the posterior by less than 1σ.
  • The preferred parameter space for axions is nearing exclusion by other astrophysical constraints.

Conclusions:

  • X-ray pulsation structures offer valuable insights into axion properties and couplings.
  • Further reduction in pulsation data uncertainties (aiming for 75%) could lead to a >3σ conclusion on axion-induced X-rays.
  • Continued study is crucial for definitively confirming or excluding axion signals from neutron stars.