Velocity peaks and caustic rings

The late infall of cold dark matter onto an isolated galaxy produces flows with definite local velocity vectors throughout the galactic halo. It also produces caustic rings, which are places in the halo where the dark matter density is very large. The self-similar model of halo formation predicts that the caustic ring radii $a_n$ follow the approximate law $a_n \simeq 1/n$. I interpret bumps in the rotation curves of NGC 3198 and of our own galaxy as due to caustic rings of dark matter. In this model of our halo the annual modulation effect in direct searches for WIMPs has the opposite sign from that predicted by the isothermal sphere model.Comment: 8 pages, 1 figure, to appear in the Proceedings of the 2d International Workshop on the Identification of Dark Matter, Buxton, England, Sept. 7-11, 199

Evidence for Ring Caustics in the Milky Way

The late infall of cold dark matter onto our galaxy produces discrete flows and caustics in its halo. The recently discovered ring of stars near galactocentric distance 20 kpc and a series of sharp rises in the Milky Way rotation curve are interpreted as due to the presence of caustic rings of dark matter in the galactic plane. Their locations are consistent at the 3% level with the predictions of the self-similar infall model for the caustic ring radii. Also, a triangular feature in the IRAS map of the galactic plane is consistent with the imprint of a caustic ring of dark matter upon the baryonic matter. These observations imply that the dark matter in our neighborhood is dominated by a single flow whose density and velocity vector are estimated.Comment: 12 pages, 2 figures. Version to be published in Phys. Lett. B. The paper has been revised in response to comments by referees and to include fresh evidenc

Axions and their Distribution in Galactic Halos

Axion physics is briefly reviewed. Constraints from laboratory searches, astrophysics and cosmology require the axion mass to be in the range $10^{-6} \lesssim m_a < 3\cdot 10^{-3}$eV. Near the lower end of this range, axions are all or a major component of the cold dark matter of the universe. The late infall of axions, and of any other cold dark matter particles, onto our galaxy produces streams and caustics in its halo. The outer caustics are topological spheres whereas the inner caustics are rings. The self-similar model of galactic halo formation predicts that the caustic ring radii $a_n$ obey the approximate law $a_n \sim 1/n$. Evidence for this law has been found in a statistical study of 32 extended and well-measured external galactic rotation curves, and in the existence and distribution of sharp rises in the Milky Way rotation curve. Moreover, a triangular feature in the IRAS map of the Galactic plane is consistent with the imprint of a ring caustic upon the baryonic matter. Its position coincides with a rise in the rotation curve, the one nearest to us. These observations imply that the dark matter in our neighborhood is dominated by a single flow. Estimates of that flow's density and velocity vector are given.Comment: 10 pages, 1 figure, invited talk at the IDM2002 conference, September 2-6, 2002 in York, Englan

Dark matter axions and caustic rings

Contents: 1. The strong CP problem 2. Dark matter axions 3. The cavity detector of galactic halo axions 4. Caustic rings in the density distribution of cold dark matter halosComment: 12 pages, Latex, one eps figure, talk at the Workshop "Beyond the Desert '97" at Castle Ringberg, Tegernsee, Germany, June 8-14, 199

The Case for Axion Dark Matter

Dark matter axions form a rethermalizing Bose-Einstein condensate. This provides an opportunity to distinguish axions from other forms of dark matter on observational grounds. I show that if the dark matter is axions, tidal torque theory predicts a specific structure for the phase space distribution of the halos of isolated disk galaxies, such as the Milky Way. This phase space structure is precisely that of the caustic ring model, for which observational support had been found earlier. The other dark matter candidates predict a different phase space structure for galactic halos.Comment: 4 pages, no figure

The Search for Dark Matter Axions

Axions solve the Strong CP Problem and are a cold dark matter candidate. The combined constraints from accelerator searches, stellar evolution limits and cosmology suggest that the axion mass is in the range $3 \cdot 10^{-3} > m_a > 10^{-6}$ eV. The lower bound can, however, be relaxed in a number of ways. I discuss the constraint on axion models from the absence of isocurvature perturbations. Dark matter axions can be searched for on Earth by stimulating their conversion to microwave photons in an electromagnetic cavity permeated by a magnetic field. Using this technique, limits on the local halo density have been obtained by the Axion Dark Matter eXperiment.Comment: 10 pages, invited talk at the 41st Rencontre de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, March 11-18, 2006. Three references were adde

Axion detection in the milli-eV mass range

We propose an experimental scheme to search for galactic halo axions with mass $m_a \sim 10^{-3}$eV, which is above the range accessible with cavity techniques. The detector consists of a large number of parallel superconducting wires embedded in a material transparent to microwave radiation. The wires carry a current configuration which produces a static, inhomogeneous magnetic field $\vec{B}_0(\vec{x})$ within the detector volume. Axions which enter this volume may convert to photons. We discuss the feasibility of the detector and its sensitivity.Comment: LaTex, 9 pages, 4 figures (sent upon request), UFIFT-HEP-93--