Cosmology; Axions are dark matter? (Introduction)

by David Turell , Monday, January 11, 2016, 01:08 (3027 days ago) @ David Turell

Another candidate for dark matter. We've had gravitinos, WIMPS, and now Axions:- https://www.quantamagazine.org/20160107-arrow-of-time-axions/-"The theory of axions predicts, in a general way, that axions should be very light, very long-lived particles whose interactions with ordinary matter are very feeble. But to compare theory and experiment we need to be quantitative. And here we meet ambiguity, because existing theory does not fix the value of the axion's mass. If we know the axion's mass we can predict all its other properties. But the mass itself can vary over a wide range. (The same basic problem arose for the charmed quark, the Higgs particle, the top quark and several other others. Before each of those particles was discovered, theory predicted all of its properties except for the value of its mass.) It turns out that the strength of the axion's interactions is proportional to its mass. So as the assumed value for axion mass decreases, the axion becomes more elusive.-***-"The experimental search for axions continues on several fronts. Two of the most promising experiments are aimed at detecting the axion fluid. One of them, ADMX (Axion Dark Matter eXperiment) uses specially crafted, ultrasensitive antennas to convert background axions into electromagnetic pulses. The other, CASPEr (Cosmic Axion Spin Precession Experiment) looks for tiny wiggles in the motion of nuclear spins, which would be induced by the axion fluid. Between them, these difficult experiments promise to cover almost the entire range of possible axion masses.-"Do axions exist? We still don't know for sure. Their existence would bring the story of time's reversible arrow to a dramatic, satisfying conclusion, and very possibly solve the riddle of the dark matter, to boot. The game is afoot."