Photon evolution through light-particle conversion in stochastic magnetic fields: Kramers--Kronig relations and universality
Abstract
We study photon conversion into light particles, such as dilatons, axions, and gravitons, induced by background magnetic fields, and formulate the resulting evolution in terms of the Stokes parameters. We show that photon conversion reduces to an effective non-unitary evolution of the photon sector. In the perturbative regime, the Hermitian and anti-Hermitian parts of the effective photon Hamiltonian are related through Kramers--Kronig relations, revealing that the changes in the Stokes parameters are not independent. We apply this general framework to photon evolution in Gaussian stochastic magnetic fields with possible helicity, and derive the ensemble-averaged evolution of the Stokes parameters. We find that two nonzero contributions arise even in the absence of magnetic helicity, which respectively correspond to the overall attenuation of all the Stokes parameters and to an irrelevant overall phase. We also find that magnetic helicity gives rise to two additional contributions, one of which changes the circular polarization while the other induces a rotation of linear polarization. These contributions form two Kramers--Kronig pairs. In particular, photon conversion induced by magnetic helicity is accompanied by both circular-polarization and birefringent responses. The same structure appears in dilaton-photon, axion-photon, and graviton-photon systems, revealing universality of photon conversion in magnetic fields.
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BibTeX
@misc{chiba2026photon,
title = {{Photon evolution through light-particle conversion in stochastic magnetic fields: Kramers--Kronig relations and universality}},
author = {Wataru Chiba and Ryusuke Jinno and Kimihiro Nomura},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.11346},
eprint = {2610.11346},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.11346},
}
RIS
TY - UNPB
TI - Photon evolution through light-particle conversion in stochastic magnetic fields: Kramers--Kronig relations and universality
AU - Wataru Chiba
AU - Ryusuke Jinno
AU - Kimihiro Nomura
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.11346
UR - https://arxiv.org/abs/2610.11346
AB - We study photon conversion into light particles, such as dilatons, axions, and gravitons, induced by background magnetic fields, and formulate the resulting evolution in terms of the Stokes parameters. We show that photon conversion reduces to an effective non-unitary evolution of the photon sector. In the perturbative regime, the Hermitian and anti-Hermitian parts of the effective photon Hamiltonian are related through Kramers--Kronig relations, revealing that the changes in the Stokes parameters are not independent. We apply this general framework to photon evolution in Gaussian stochastic magnetic fields with possible helicity, and derive the ensemble-averaged evolution of the Stokes parameters. We find that two nonzero contributions arise even in the absence of magnetic helicity, which respectively correspond to the overall attenuation of all the Stokes parameters and to an irrelevant overall phase. We also find that magnetic helicity gives rise to two additional contributions, one of which changes the circular polarization while the other induces a rotation of linear polarization. These contributions form two Kramers--Kronig pairs. In particular, photon conversion induced by magnetic helicity is accompanied by both circular-polarization and birefringent responses. The same structure appears in dilaton-photon, axion-photon, and graviton-photon systems, revealing universality of photon conversion in magnetic fields.
ER -