Impedance matching to axion dark matter: considerations of the photon-electron interaction

We introduce the concept of impedance matching to axion dark matter by posing question why detection is difficult, even though there enough power in each square meter incident dark-matter flux energize a LED light bulb. By quantifying backreaction on field, we show that small axion-photon coupling does not itself prevent an order-unity fraction from being absorbed through optimal match. further show, contrast, electromagnetic charges and self-impedance their photons provide principal constraint absorption integrated across search band. Using equations electrodynamics, demonstrate stringent limitations linear, time-invariant, passive receivers. Our results yield fundamental constraints, arising photon-electron interaction, improving beyond cavity haloscope technique. The analysis also has significant practical implications, showing apparent tension with sensitivity projections for number planned searches. additionally basis more accurate signal calculations calibration models, especially receivers using multi-wavelength open configurations such as dish antennas dielectric haloscopes.