Photon propagation through axion clouds around magnetized compact objects: time delays and polarimetric signatures
- 1Department of Physics, University of Helsinki and Helsinki Institute of Physics
- 2Departamento de Física, UFMG
Abstract
Temporal offsets between Gamma-Ray Bursts (GRBs) and high-energy neutrinos probe propagation effects in extreme astrophysical environments. We investigate whether such offsets can be generated by photon propagation through dense axion clouds gravitationally bound to strongly magnetized compact objects, such as canonical pulsars. Working within the Euler-Heisenberg effective theory extended by the axion sector, we derive the photon dispersion relations in a strong magnetic background permeated by an oscillating axion field. The magnetized vacuum is birefringent already at the Euler-Heisenberg level and the axion cloud superimposes density-dependent, time-dependent, and parity-odd structure on this baseline. The resulting geometry-dependent deviations from luminal propagation yield kinematic time delays reaching ∆t⊥ ≃ 9.3 × 10−12 s for k ⊥ B, far too small to account for macroscopic multimessenger offsets, so that propagation through such environments cannot, by itself, rule out Lorentz-invariance violation as an explanation for GRB offsets. In the polarization sector, we show that the axion-induced circular birefringence is an endpoint effect and therefore does not produce a leading net rotation for a complete vacuum-to-vacuum transit through a localized cloud. For configurations with a nonzero axion-field endpoint contrast, the same parity-odd phase defines a conditional environmental sensitivity benchmark. We find that this mechanism is optimally sensitive in the ultralight regime, yielding a benchmark reach of gaγγ ≲ 2.5 × 10−10 GeV−1 for canonical pulsar fields and axion masses near ma ∼ 10−9 eV, and we identify the parity-odd (chiral) birefringence induced by the oscillating cloud as the signature that distinguishes the axion contribution from the calculable QED baseline.
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BibTeX
@article{chaichian2026photon,
title = {{Photon propagation through axion clouds around magnetized compact objects: time delays and polarimetric signatures}},
author = {Moshe M. Chaichian and Bruno A. Couto e Silva and Bruce L. Sánchez-Vega},
journal = {Journal of High Energy Physics},
year = {2026},
month = nov,
doi = {10.1007/jhep11(2026)012},
url = {https://link.springer.com/article/10.1007/JHEP11(2026)012},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Photon propagation through axion clouds around magnetized compact objects: time delays and polarimetric signatures
AU - Moshe M. Chaichian
AU - Bruno A. Couto e Silva
AU - Bruce L. Sánchez-Vega
PY - 2026
DA - 2026/11/02
JO - Journal of High Energy Physics
DO - 10.1007/jhep11(2026)012
UR - https://link.springer.com/article/10.1007/JHEP11(2026)012
AB - Temporal offsets between Gamma-Ray Bursts (GRBs) and high-energy neutrinos probe propagation effects in extreme astrophysical environments. We investigate whether such offsets can be generated by photon propagation through dense axion clouds gravitationally bound to strongly magnetized compact objects, such as canonical pulsars. Working within the Euler-Heisenberg effective theory extended by the axion sector, we derive the photon dispersion relations in a strong magnetic background permeated by an oscillating axion field. The magnetized vacuum is birefringent already at the Euler-Heisenberg level and the axion cloud superimposes density-dependent, time-dependent, and parity-odd structure on this baseline. The resulting geometry-dependent deviations from luminal propagation yield kinematic time delays reaching ∆t⊥ ≃ 9.3 × 10−12 s for k ⊥ B, far too small to account for macroscopic multimessenger offsets, so that propagation through such environments cannot, by itself, rule out Lorentz-invariance violation as an explanation for GRB offsets. In the polarization sector, we show that the axion-induced circular birefringence is an endpoint effect and therefore does not produce a leading net rotation for a complete vacuum-to-vacuum transit through a localized cloud. For configurations with a nonzero axion-field endpoint contrast, the same parity-odd phase defines a conditional environmental sensitivity benchmark. We find that this mechanism is optimally sensitive in the ultralight regime, yielding a benchmark reach of gaγγ ≲ 2.5 × 10−10 GeV−1 for canonical pulsar fields and axion masses near ma ∼ 10−9 eV, and we identify the parity-odd (chiral) birefringence induced by the oscillating cloud as the signature that distinguishes the axion contribution from the calculable QED baseline.
SN - 1029-8479
ER -