S.J. Asztalos

SQUID-Based Microwave Cavity Search for Dark-Matter Axions

Axions in the microeV mass range are a plausible cold dark-matter candidate and may be detected by their conversion into microwave photons in a resonant cavity immersed in a static magnetic field. We report the first result from such an axion search using a superconducting first-stage amplifier (SQUID) replacing a conventional GaAs field-effect transistor amplifier. This experiment excludes KSVZ dark-matter axions with masses between 3.3 microeV and 3.53 microeV and sets the stage for a definitive axion search utilizing near quantum-limited SQUID amplifiers.

Experimental Constraints on the Axion Dark Matter Halo Density

Most of the mass of the Milky Way is contributed by its halo, presumably in the form of noninteracting cold dark matter. The axion is a compelling cold dark matter candidate. We report results from a search that probes the local Galactic halo axion density using the Sikivie radio frequency cavity technique. Candidates over the frequency range 550 MH MHz (2.3 me meV) were investigated. The absence of a signal z ≤ f ≤ 810 V ≤ m ≤ 3.4 a suggests that the axions of Kim and Shifman, Vainshtein, & Zakharov contribute no more than 0.45 GeV cm 3 of mass density to the local dark matter halo over this mass range. Subject headings: dark matter — Galaxy: halo — instrumentation: detectors

Search for Hidden Sector Photons with the ADMX Detector

Hidden U(1) gauge symmetries are common to many extensions of the standard model proposed to explain dark matter. The hidden gauge vector bosons of such extensions may mix kinetically with standard model photons, providing a means for electromagnetic power to pass through conducting barriers. The axion dark matter experiment detector was used to search for hidden vector bosons originating in an emitter cavity driven with microwave power. We exclude hidden vector bosons with kinetic couplings χ>3.48×10⁻⁸ for masses less than 3  μeV. This limit represents an improvement of more than 2 orders of magnitude in sensitivity relative to previous cavity experiments.

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 � * 0:2 GeV=cm 3 and Dine-Fischler-Srednicki-Zhitnitskii densities of � * 1:4 GeV=cm 3 over a mass range of ma ¼ 3:3 � eV to 3:69 � eV for models having velocity dispersions of � � & 3 � 10 � 6 .

Search for Chameleon Scalar Fields with the Axion Dark Matter Experiment

Scalar fields with a chameleon property, in which the effective particle mass is a function of its local environment, are common to many theories beyond the standard model and could be responsible for dark energy. If these fields couple weakly to the photon, they could be detectable through the afterglow effect of photon-chameleon-photon transitions. The ADMX experiment was used in the first chameleon search with a microwave cavity to set a new limit on scalar chameleon-photon coupling beta_gamma excluding values between 2x109 and 5x1014 for effective chameleon masses between 1.9510 and 1:9525 micro eV.