Linear Mode Conversion in Ultramagnetized Pair Plasmas: Single-Parameter Scaling

TL;DR

This paper develops a unified theory of linear mode conversion in ultramagnetized pair plasmas, revealing how magnetic geometry and a single parameter control wave mode transitions relevant to neutron star observations.

Contribution

It introduces a comprehensive model of mode conversion that accounts for magnetic field geometry and identifies a universal parameter governing efficiency.

Findings

Magnetic field-line curvature induces specific mode conversions.

A single parameter controls both low- and high-frequency conversion channels.

Conversion efficiency follows a universal nonadiabatic transition probability.

Abstract

In neutron star (NS) magnetospheres, plasma waves propagate as normal modes with distinct propagation dynamics that strongly influence observable signals. This letter presents a unified theory of linear mode conversion between Alfv'en (A), superluminal ordinary (O), and extraordinary (X) modes, incorporating the effect of magnetic-field geometry and local plasma response. Magnetic field-line curvature induces A-X conversion for low frequencies and O-X conversion at high frequencies, whereas plasma gradients alone do not drive X-mode coupling. We show that a single dimensionless parameter controls both conversion channels. The conversion efficiency follows the universal nonadiabatic transition probability of a multilevel quantum system. Efficient conversion occurs within a narrow angular window between the wave vector and magnetic field, localizing potential conversion sites in the NS magnetosphere. This linear mechanism naturally accounts for complex polarization features observed in pulsars and some fast radio bursts.