The Darkfield Array: A Microwave Photonic Search for Novel Physics

The Darkfield Array is a proposed laboratory search for hidden photons, hypothetical gauge bosons that could constitute a component of dark matter [1]. Motivated by the need for a controlled test of narrowband GHz anomalies reported in the wider microwave literature - features that can mimic new physics signals without stringent controls - Darkfield will probe whether such phenomena could arise from photon–hidden-photon kinetic mixing [2–4].. Darkfield employs a straightforward binary logic: a collected astrophysical microwave beam (no discrete source is required; the dish is a well-characterised input and enables off-source nods) is intercepted by a solid RF wall that suppresses ordinary electromagnetic radiation below the downstream detection floor, while any hidden-photon component traverses unhindered. Downstream, a tunable plasma cell is adjusted so that its plasma frequency matches the candidate hidden-photon mass, enabling reconversion into real microwaves. These regenerated signals are then recorded with an ultra-low-noise detection chain. This white paper outlines the scientific background, theoretical basis, instrument design, and analysis plan for Darkfield. The experiment will either confirm the presence of hidden photons in the 8–18 GHz (≈33–74 µeV) baseline mass range, with staged extensions to 18–26.5 GHz and 26.5–40 GHz (up to ≈165 µeV) where technically viable, or, in the absence of a detection, set new exclusion limits on the kinetic mixing parameter at the 10⁻¹²–10⁻¹³ level [3,4]. In both outcomes, Darkfield provides a clear, laboratory-based test of hidden-photon physics in a frequency regime that remains largely unexplored. Throughout, we target hidden photons; axion-specific hardware and interpretation are deferred to future work. Darkfield is conceived not as a competitor to large facilities, but as a complementary, low-cost probe of the 8–18 GHz baseline band (with staged extensions up to ~40 GHz), providing a decisive way either to reveal hidden photons or to close a poorly tested gap in the dark-sector parameter space. [3,4]