Constraints on cosmic-ray observation of Cygnus X-3

Two experimental groups1,2 working at different minimum energies have reported underground muons coming from the direction of Cygnus X-3 with rates that vary in synchrony with its binary period. The depths involved are such that the muons have energies of the order of 1 TeV for the shallower1 and several TeV for the deeper2 detector. Such observations, if verified, would require a new particle or a new physical process3. Here we explore our earlier suggestion4 that the new signal carrier could be a neutral bit of quark matter, condensed and stabilized by strange quarks. We also consider other, more general explanations and conclude that it is exceedingly difficult to find a self-consistent explanation of the observations.