Theory Update 8

The idea of mirror matter is an old one. It is usually discussed in terms of the Standard Model, complete with fairy fields, but we can nonetheless peruse the study of its observational consequences with interest.

For example, long time mirror matter researchers such as R. Foot have considered it as an explanation for the positive DAMA dark matter results. More recently, a paper on neutron mirror neutron oscillations notes that

Bento and Berezhiani [noted] that if these oscillations occurred at a rate of $\tau^{-1} \sim 1 s^{-1}$, it would help explain putative super GZK cosmic ray events, provided the temperature of the mirror radiation is $\sim 0.3 - 0.4$ times that of the familiar cosmic microwave background radiation.

Conveniently, the Koide masses suggest that the mirror temperature would be around $0.3248$ times that of the CMB, namely $0.885$ K, since the mirror antineutrino has the mass of the lightest ordinary neutrino.