Dark Photon Polarimetry

TL;DR

This paper proposes a novel method using polarimetry to detect dark photons, a dark matter candidate, by analyzing their effects on electromagnetic signals, and applies it to data from the Event Horizon Telescope to set new constraints.

Contribution

It introduces a polarimetric detection technique for dark photons and demonstrates its application to astrophysical data to establish new limits on dark photon properties.

Findings

Set new limits on dark photon mass ranges using EHT data.

Demonstrated the feasibility of DP detection via polarimetry in astrophysical observations.

Identified potential for broad application in laboratory and astronomical searches.

Abstract

We propose detecting dark photons (DP), a major candidate for wave dark matter, through polarimetry. The DP can modify Maxwell's equations due to its kinetic mixing with regular photons, inducing an oscillating component in the electromagnetic field. This may leave an imprint on polarimetric light signals, such as Faraday rotation, characterized by a distinctive wave pattern in spacetime. We then apply this method to investigate ultralight DPs produced through the superradiance of supermassive black holes for demonstration. Using the polarimetric measurements of radiation from the M87$^\ast$ and Sgr A$^\ast$ at the Event Horizon Telescope, we show that novel limits on the photon-DP mixing parameter can be set for the rarely-explored DP mass ranges: explicitly $10^{-22} - 10^{-20}\,$eV with the best reach of $\sim 10^{-8}$ achieved at $\sim 10^{-20}$eV, and $10^{-19} - 10^{-17}\,$eV with the best reach of $\sim 10^{-11}$ achieved at $\sim 10^{-17}$eV. Given the universality of its underlying physics, we expect DP polarimetry to be broadly applicable for DP detection in laboratory experiments and astronomical observations.