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arXiv · 2602.03953

Ultralight time-oscillating scalars from magnetized compact stars: electrophilic radiation and photon propagation effects

Tanmay kumar Poddar·Gaetano Lambiase
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Abstract

Ultralight scalars with electrophilic couplings to the time-dependent Goldreich-Julian charge density of magnetized compact stars can be radiated from their magnetospheres, contributing to pulsar spin-down. Coupling to the time-independent component of the charge density instead generates a quadrupolar scalar field profile, which may influence the orbital dynamics of binary systems. Such scalars can also interact with the time-varying electromagnetic fields of magnetized stars, modifying photon propagation and inducing observable effects in the redshift and residual time-delay measurements, as well as corrections to the background electromagnetic fields. We investigate these phenomena for the Crab pulsar, SGR 1806-20, and GRB 080805A. Using spectral and timing observations, we derive constraints on the scalar-electron and scalar-photon couplings. While the bounds obtained on the scalar-electron coupling from pulsar spin-down are weaker than existing limits, electromagnetic radiation measurements yield the strongest astrophysical constraints to date on the scalar-photon coupling. Compact stars with stronger surface magnetic fields and observations at lower photon frequencies can improve these bounds by several orders of magnitude.

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Tanmay kumar Poddar, Gaetano Lambiase. 2026-02-03. Ultralight time-oscillating scalars from magnetized compact stars: electrophilic radiation and photon propagation effects. https://arxiv.org/abs/2602.03953

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