ADAMOS: Axion Daily Modulation Searches for Dark Matter at 20 GHz

Abstract

The ADAMOS (Axion Daily Modulation Searches) project aims to explore the nature of dark matter (DM) through a novel axion haloscope experiment. We propose to construct a fixed-frequency cavity resonator operating at 20 GHz at the University of Hamburg, using an innovative "thin-shell" design that preserves a large detection volume at high frequencies. The experiment will be installed in an existing 14 T superconducting magnet and connected to a highly sensitive RF chain with continuous in situ calibration to eliminate temperature-dependent gain drifts, constituting an essential improvement based on lessons learned from previous attempts. ADAMOS will conduct simultaneous searches for three classes of axion signals: (1) conventional cold DM axions, (2) relativistic axions from axion quark nugget annihilations exhibiting daily modulations, and (3) transient enhancements from streaming DM. By targeting this unexplored frequency regime with a robust, calibrated, and versatile setup, ADAMOS will open new discovery channels in a previously unexplored region of the dark sector.

Figures (9)

• Figure 1: Comparison of AQN-induced (red) and CDM (blue) axion spectral shapes at 20. The AQN signal is relativistic and broadband ($\Delta f/f \sim 1$), while the CDM signal is a boosted Maxwellian with a FWHM of $\sim36\kHz$ ($\Delta f/f \sim 10^{-6}$), accounting for terrestrial motion. Note the dual frequency scales: the bottom axis covers 1 for CDM, while the top axis spans 10 for AQN.
• Figure 2: Schematic internal structure of an AQN. The color superconducting (SC) quark core ($R \sim 10^{-5}$ cm, $B \sim 10^{25}$), in brown, is bounded by a thin QCD substructure, in red, ($\Delta R_{\text{QCD}} \sim 10^{-13}$ cm) and an electrosphere ($\Delta R_e \sim 10^{-8}$ cm), in pink. The nugget is stabilized by the pressure of an ADW in gold, where hydrostatic equilibrium is maintained by the balance of $P_{\text{ADW}}$ and $P_{\text{Fermi}}$. For an axion mass of $m_a \approx 82.7µ\eV$ the characteristic radius $R_{\text{ADW}} \propto m_a^{-1} \sim O(1)~\cm$. The radial reference axis is logarithmic in the absolute radius $R$ to illustrate the large hierarchy between the microscopic core and the macroscopic ADW. The QCD substructure and electrosphere are shown as finite layers for visual clarity, while their thicknesses $\Delta R \ll R$ are not drawn to scale. Adapted from Zhitnitsky_2023_structure.
• Figure 3: Daily modulation mechanism for AQN-related axions. The 63° inclination of the DM wind, originating from the galactic plane relative to the celestial equator, results in approximately 10% more axions being emitted toward the upper hemisphere than the lower. As the Earth rotates, this anisotropy leads to a detectable $\sim$10% daily modulation in the axion signal. The modulation amplitude is further enhanced for detectors located at lower latitudes Liang_aqn_2020.
• Figure 4: 3D model of the ADAMOS cavity. The thin-shell geometry consists of two concentric cylinders with a uniform 7.5 gap, which defines the annular volume where the pseudo-TM$_{010}$ mode is supported.
• Figure 5: Simulation of the distribution of the fundamental pseudo-TM$_\text{010}$ mode inside the empty ADAMOS cavity (left) and with the two input and output antennas (right) using CST Studio Suite. The color scale indicates the normalized electric field magnitude, with red representing the maximum field intensity.