Search for nonvirialized axionic dark matter

Cold dark matter in the Milky Way halo may have structure defined by flows with low velocity dispersion. The Axion Dark Matter eXperiment high resolution channel is especially sensitive to axions in such low velocity dispersion flows. Results from a combined power spectra analysis of the high resolution channel axion search are presented along with a discussion of the assumptions underlying such an analysis. We exclude Kim-Shifman-Vainshtein-Zakharov axion dark matter densities of $\rho \gtrsim 0.2\mathrm{GeV}/{\mathrm{cm}}^3$ and Dine-Fischler-Srednicki-Zhitnitskii densities of $\rho \gtrsim 1.4\mathrm{GeV}/{\mathrm{cm}}^3$ over a mass range of $m_a=3.3\mu \mathrm{eV}$ to $3.69\mu \mathrm{eV}$ for models having velocity dispersions of $\Delta \beta \lesssim 3\times {10}^{-6}$.

Figure 1

Diagram of the ADMX cavity and receiver chain. The power read out from the cavity is sent through both cold and room temperature amplification stages, is mixed down from radio frequencies to audio frequencies via two local oscillators (L.O.), and is ultimately saved to disk.

Figure 2

Monte Carlo simulations of nonvirialized axion signals imposed on real HR data. The broader peak (velocity dispersion of $2\times {10}^{-4}$) is shown as an example of the narrowest signal that the MR channel can resolve. An excess power of 0 corresponds to power in that bin equal to the rms noise power at that frequency.

Figure 3

An example of a modulation-insensitive power spectrum after the crystal filter shape and amplifier chain effects have been divided out. The insert shows the raw power spectrum with a passband shape imparted by the crystal filter.

Figure 4

Density limits for the HR channel ($\Delta \beta \lesssim 3\times {10}^{-6}$) at 90% confidence from 812 MHz to 892.8 MHz. The scale for limits on KSVZ and DFSZ axions are shown on the left and right axes, respectively. Density limits for the currently published MR channel data ($\Delta \beta \lesssim 2\times {10}^{-4}$) [23] are shown for comparison.