Photon-dark photon oscillation in M87 and Crab Nebula environments

TL;DR

This paper investigates how resonant photon-dark photon oscillations in astrophysical environments like M87 and Crab Nebula can set new constraints on dark photon properties, surpassing some existing limits through analysis of spectral data.

Contribution

It demonstrates that realistic plasma density profiles in astrophysical objects enhance photon-dark photon conversion, leading to stronger constraints on kinetic mixing parameters.

Findings

Derived bounds on dark photon kinetic mixing from M87* and Crab Nebula data.

Showed non-monotonic plasma profiles increase resonant conversion efficiency.

Provided constraints that surpass existing astrophysical limits at certain masses.

Abstract

Compact astrophysical systems such as neutron stars and black holes provide powerful laboratories for testing feebly coupled dark photons (DPs). We investigate light DPs kinetically mixed with the visible photon that need not be the dark matter, focusing on resonant photon-DP oscillations in magnetized, modeled plasma environments. We show that realistic non-monotonic plasma density profiles generically enhance resonant conversion relative to monotonic models, leading to substantially stronger constraints on the photon-DP kinetic mixing parameter ($\epsilon$). Using spectral data from the supermassive black hole (SMBH) M87*, extending to the LOFAR band, we derive a bound $\epsilon \simeq 7\times10^{-6}$ at the DP mass $m_{A'} \simeq 5\times10^{-7}\,\mathrm{eV}$ for oscillation distance $3r_{\rm ph}$, where $r_{\rm ph}$ denotes the photon sphere radius. From the Crab pulsar-wind Nebula, we obtain an even stronger constraint, $\epsilon \simeq 8\times10^{-7}$ at $m_{A'} \simeq 4\times10^{-9}\,\mathrm{eV}$ for oscillation baselines of order $10^{3}\,\mathrm{km}$, surpassing existing astrophysical limits in realistic plasma backgrounds. While laboratory and cosmological bounds remain slightly stronger at comparable masses, observation of compact objects with larger surface magnetic fields and measurements of photon spectra at lower frequencies would enhance the limits on the photon-DP coupling by orders of magnitude.