Dark matter axions may cause transitions between atomic states that differ in energy by an amount equal to the axion mass. Such energy differences are conveniently tuned using the Zeeman effect. It ...is proposed to search for dark matter axions by cooling a kilogram-sized sample to millikelvin temperatures and count axion induced transitions using laser techniques. This appears to be an appropriate approach to axion dark matter detection in the 10^{-4} eV mass range.
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.
We show that cold dark matter axions thermalize and form a Bose-Einstein condensate (BEC). We obtain the axion state in a homogeneous and isotropic universe, and derive the equations governing small ...axion perturbations. Because they form a BEC, axions differ from ordinary cold dark matter in the nonlinear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles.
We show that dark matter axions cause an oscillating electric current to flow along magnetic field lines. The oscillating current induced in a strong magnetic field B0 produces a small magnetic field ...Ba. We propose to amplify and detect Ba using a cooled LC circuit and a very sensitive magnetometer. This appears to be a suitable approach to searching for axion dark matter in the 10(-7) to 10(-9) eV mass range.
We analyze the behavior of axion dark matter before it falls into a galactic gravitational potential well. The axions thermalize sufficiently fast by gravitational self-interactions that almost all ...go to their lowest-energy state consistent with the total angular momentum acquired from tidal torquing. That state is a state of rigid rotation on the turnaround sphere. It predicts the occurrence and detailed properties of the caustic rings of dark matter for which observational evidence had been found earlier. We show that the vortices in the axion Bose-Einstein condensate (BEC) are attractive, unlike those in superfluid super(4)He and dilute gases. We expect that a large fraction of the vortices in the axion BEC join into a single big vortex along the rotation axis of the galaxy. The resulting enhancement of caustic rings explains the typical size of the rises in the Milky Way rotation curve attributed to caustic rings. We show that baryons and ordinary cold dark matter particles are entrained by the axion BEC and acquire the same velocity distribution. The resulting baryonic angular momentum distribution gives a good qualitative fit to the distributions observed in dwarf galaxies. We give estimates of the minimum fraction of dark matter that is composed of axions.
Cosmic axion thermalization Erken, O.; Sikivie, P.; Tam, H. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
03/2012, Letnik:
85, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Axions differ from the other cold dark matter candidates in that they form a degenerate Bose gas. It is shown that their huge quantum degeneracy and large correlation length cause cold dark matter ...axions to thermalize through gravitational self-interactions when the photon temperature reaches approximately 500 eV. When they thermalize, the axions form a Bose-Einstein condensate. Their thermalization occurs in a regime, herein called the "condensed regime," where the Boltzmann equation is not valid because the energy dispersion of the particles is smaller than their interaction rate. We derive analytical expressions for the thermalization rate of particles in the condensed regime, and check the validity of these expressions by numerical simulation of a toy model. We revisit axion cosmology in light of axion Bose-Einstein condensation. It is shown that axions are indistinguishable from ordinary cold dark matter on all scales of observational interest, except when they thermalize or rethermalize. The rethermalization of axions that are about to fall in a galactic potential well causes them to acquire net overall rotation as they go to the lowest energy state consistent with the total angular momentum they acquired by tidal torquing. This phenomenon explains the occurrence of caustic rings of dark matter in galactic halos. We find that photons may reach thermal contact with axions and we investigate the implications of this possibility for the measurements of cosmological parameters.
Axions are a promising cold dark matter candidate. Haloscopes, which use the conversion of axions to photons in the presence of a magnetic field to detect axions, are the basis of microwave cavity ...searches such as the Axion Dark Matter eXperiment (ADMX). To search for lighter, low frequency axions in the sub- 2 × 10 − 7 eV (50 MHz) range, a tunable lumped-element LC circuit has been proposed. For the first time, through ADMX SLIC (Superconducting LC Circuit Investigating Cold Axions), a resonant LC circuit was used to probe this region of axion mass-coupling space. The detector used a superconducting LC circuit with piezoelectric driven capacitive tuning. The axion mass and corresponding frequency ranges 1.7498 – 1.7519 × 10 − 7 eV (42.31–42.36 MHz), 1.7734 – 1.7738 × 10 − 7 eV (42.88–42.89 MHz), and 1.8007 – 1.8015 × 10 − 7 eV (43.54–43.56 MHz) were covered at magnetic fields of 4.5 T, 5.0 T, and 7.0 T, respectively. Exclusion results from the search data, for coupling below 10 − 12 GeV − 1 , are presented.
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.
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