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Register a new userModulation Sensitive Search for Non-Virialized Dark-Matter Axions
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Non-virialized dark-matter axions may be present in the Milky Way halo in the form of low-velocity-dispersion flows. The Axion Dark Matter eXperiment performed a search for the conversion of these axions into microwave photons using a resonant cavity immersed in a strong, static magnetic field. The spread of photon energy in these measurements was measured at spectral resolutions of the order of 1 Hz and below. If the energy variation were this small, the frequency modulation of any real axion signal due to the orbital and rotational motion of the Earth would become non-negligible. Conservative estimates of the expected signal modulation were made and used as a guide for the search procedure. The photon frequencies covered by this search are 812$-$852 and 858$-$892 MHz, which correspond to an axion mass of 3.36$-$3.52 and 3.55$-$3.69 {mu}eV. No axion signal was found, and limits were placed on the maximum local density of non-virialized axions of these masses.
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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 KSVZ axion dark matter densities of {rho} > 0.2 GeV/cm^3 and DFSZ densities of {rho} > 1.4 GeV/cm^3 over a mass range of m_a = 3.3{mu}eV to 3.69{mu}eV for models having velocity dispersions of {Delta}{beta} < 3x10^-6.
Axions in the micro eV 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. The first result from such an axion search using a superconducting first-stage amplifier (SQUID) is reported. The SQUID amplifier, replacing a conventional GaAs field-effect transistor amplifier, successfully reached axion-photon coupling sensitivity in the band set by present axion models and sets the stage for a definitive axion search utilizing near quantum-limited SQUID amplifiers.
We suggest a new approach to search for galactic axions or other similar exotica. Streaming dark matter (DM) could have a better discovery potential because of flux enhancement, due to gravitational lensing when the Sun and/or a planet are aligned with a DM stream. Of interest are also axion miniclusters, in particular, if the solar system has trapped one during its formation. Wide-band axion antennae fit this concept, but also the proposed fast narrow band scanning. A network of detectors can provide full time coverage and a large axion mass acceptance. Other DM searches may profit from this proposal.
In dark matter axion searches, quantum uncertainty manifests as a fundamental noise source, limiting the measurement of the quadrature observables used for detection. We use vacuum squeezing to circumvent the quantum limit in a search for a new particle. By preparing a microwave-frequency electromagnetic field in a squeezed state and near-noiselessly reading out only the squeezed quadrature, we double the search rate for axions over a mass range favored by recent theoretical projections. We observe no signature of dark matter axions in the combined $16.96-17.12$ and $17.14-17.28spacemutext{eV}/c^2$ mass window for axion-photon couplings above $g_{gamma} = 1.38times g_{gamma}^text{KSVZ}$, reporting exclusion at the 90% level.
Wave dark matter ($psi$DM), which satisfies the Schrodinger-Poisson equation, has recently attracted substantial attention as a possible dark matter candidate. Numerical simulations have in the past provided a powerful tool to explore this new territory of possibility. Despite their successes to reveal several key features of $psi$DM, further progress in simulations is limited, in that cosmological simulations so far can only address formation of halos below $sim 2times 10^{11} M_odot$ and substantially more massive halos have become computationally very challenging to obtain. For this reason, the present work adopts a different approach in assessing massive halos by constructing wave-halo solutions directly from the wave distribution function. This approach bears certain similarity with the analytical construction of particle-halo (cold dark matter model). Instead of many collisionless particles, one deals with one single wave that has many non-interacting eigenstates. The key ingredient in the wave-halo construction is the distribution function of the wave power, and we use several halos produced by structure formation simulations as templates to determine the wave distribution function. Among different models, we find the fermionic King model presents the best fits and we use it for our wave-halo construction. We have devised an iteration method for constructing the nonlinear halo, and demonstrate its stability by three-dimensional simulations. A Milky-Way-sized halo has also been constructed, and the inner halo is found flatter than the NFW profile. These wave-halos have small-scale interferences both in space and time producing time-dependent granules. While the spatial scale of granules varies little, the correlation time is found to increase with radius by one order of magnitude across the halo.
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