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The Suns hot corona could result from hypothetical particles converting to X-rays


(30 April, 2007)
A hypothetical elementary particle - the axion - may be flooding out of the solar core in great profusion. This particle, invented for an entirely different theoretical purpose, is a leading candidate to supply the dark matter inferred to compose the bulk of the mass in the Universe. Alas, theory does not predict the mass of the axion, but if axions do exist and if their mass is not too small, then the dark matter mystery may be solved and our understanding of the Universe greatly expanded. Accordingly many searches for this weakly-interacting particle are underway in laboratories on Earth and via astrophysical inference.

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Title: Axions as Dark Matter Particles
Authors: Leanne D. Duffy, Karl van Bibber

We review the current status of axions as dark matter. Motivation, models, constraints and experimental searches are outlined. The axion remains an excellent candidate for the dark matter and future experiments, particularly the Axion Dark Matter eXperiment (ADMX), will cover a large fraction of the axion parameter space.

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Title: Axions and the white dwarf luminosity function
Authors: J. Isern, S. Catalan, E. Garcia-Berro, S. Torres

The evolution of white dwarfs can be described as a simple cooling process. Recently, it has been possible to determine with an unprecedented precision their luminosity function, that is, the number of stars per unit volume and luminosity interval. Since the shape of the bright branch of this function is only sensitive to the average cooling rate, we use this property to check the possible existence of axions, a proposed but not yet detected weakly interacting particle. We show here that the inclusion of the axion emissivity in the evolutionary models of white dwarfs noticeably improves the agreement between the theoretical calculations and the observational white dwarf luminosity function, thus providing the first positive indication that axions could exist. Our results indicate that the best fit is obtained for m_a cos^2beta ~ 2-6 meV, where m_a is the mass of the axion and cos^2beta is a free parameter, and that values larger than 10 meV are clearly excluded.

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Title: Status report of the Tokyo axion helioscope experiment
Authors: Y. Inoue, M. Minowa, Y. Akimoto, R. Ota, T. Mizumoto, A. Yamamoto

We have searched for solar axions with a detector which consists of a 4T x 2.3m superconducting magnet, PIN-photodiode X-ray detectors, and an altazimuth mount to track the sun. The conversion region is filled with cold helium gas which modifies the axion mass at which coherent conversion occurs. In the past measurements, axion mass from 0 to 0.27eV have been scanned. Since no positive evidence was seen, an upper limit to the axion-photon coupling constant was set to be g < 6-10E-10/GeV (95%CL) depending on the axion masses. We are now actively preparing for a new stage of the experiment aiming at one to a few eV solar axions. In this mass region, our detector might be able to check parameter regions which are preferable to the axion models.

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