Speaker
Prof.
Christian Beck
(Queen Mary, University of London, School of Mathematical Sciences)
Description
This talk will be on a recent proposal that QCD dark matter axions from the galactic halo that pass through Earth can produce a small Shapiro step-like signal in Josephson junctions whose Josephson frequency resonates with the axion mass [1].
The axion field equations in a voltage-driven Josephson environment allow for a
nontrivial solution where the axion-induced electrical current manifests itself as
a supercurrent. After briefly explaining the theory I will concentrate on experimental aspects and derive a condition for the design of Josephson junction
experiments so that they can act as optimum axion detectors.
Four independent recent experiments based on different types of Josephson junctions
are discussed in this context. The observed Shapiro step anomalies of all four experiments consistently point towards an axion mass of (110 $\pm$ 2) $\mu$eV.
This mass value is compatible with the recent BICEP2 results and implies that Peccei-Quinn symmetry breaking was taking
place after inflation [2]. One can also use the signal intensity to estimate
the axionic dark matter density near the Earth to be about 0.05 GeV$/cm^3$,
although the theoretical uncertainties for this are much higher.
I will discuss future experimental checks to either confirm or refute the dark-matter nature of
the observed signals.
[1] C. Beck, Phys. Rev. Lett. 111, 231801 (2013) [arXiv:1309.3790]
[2] C. Beck, arXiv:1403.5676
Author
Prof.
Christian Beck
(Queen Mary, University of London, School of Mathematical Sciences)
