Photon-Dark Photon Conversion with Multiple Level Crossings

TL;DR

This paper investigates dark photon to SM photon conversion in complex environments with multiple resonances, revealing limitations of the Landau-Zener approximation and providing an improved analytic method for accurate probability predictions.

Contribution

It demonstrates the breakdown of the Landau-Zener approximation in multiple level-crossing scenarios and introduces a new analytic approach accounting for phase interference effects.

Findings

Landau-Zener approximation fails with multiple crossings.

Phase interference significantly affects conversion probabilities.

New analytic method accurately predicts conversion in complex environments.

Abstract

Dark photons can oscillate into Standard Model (SM) photons via kinetic mixing. The conversion probability depends sensitively on properties of the ambient background, such as the density and electromagnetic field strength, which cause the SM photon to acquire an in-medium effective mass. Resonances can enhance the conversion probability when there is a level-crossing between the dark photon and background-dependent SM photon states. In this work, we show that the widely used Landau-Zener (LZ) approximation breaks down when there are multiple level-crossings due to a non-monotonic SM photon potential. Phase interference effects, especially when the dark photon mass is close to an extremum of the SM photon effective mass, can cause deviations from the LZ approximation at the level of a few orders of magnitude in the conversion probability. We present an analytic approximation that is valid in this regime and that can accurately predict the conversion probabilities in a wide range of astrophysical environments.