Observational Effects of Mirror Matter
If mirror matter is present in the universe with sufficient abundance then its gravitational effects can be detected. Because mirror matter is analogous to ordinary matter, it is then to be expected that a fraction of the mirror matter exists in the form of mirror galaxies, mirror stars, mirror planets etc. These objects can be detected using gravitational microlensing. One would also expect that some fraction of stars have mirror objects as their companion. In such cases one should be able to detect periodic Doppler shifts in the spectrum of the star. There are some hints that such effects may already have been observed.
What if mirror matter does exist but has (almost) zero abundance? Like magnetic monopoles, mirror matter could have been diluted to unobservably low densities during the inflation epoch. Sheldon Glashow has shown that if at some high energy scale particles exist which interact strongly with both ordinary and mirror particles, radiative corrections will lead to a mixing between photons and mirror photons. This mixing has the effect of giving mirror electric charges a very small ordinary electric charge. Another effect of photon-mirror photon mixing is that it induces oscillations between positronium and mirror positronium. Positronium could then turn into mirror positronium and then decay into mirror photons.
The mixing between photons and mirror photons could be present in tree level Feynman diagrams or arise as a consequence of quantum corrections due to the presence of particles that carry both ordinary and mirror charges. In the latter case, the quantum corrections have to vanish at the one and two loop level Feynman diagrams, otherwise the predicted value of the kinetic mixing parameter would be larger than experimentally allowed.
An experiment to measure this effect is currently being planned.
If mirror matter does exist in large abundances in the universe and if it interacts with ordinary matter via photon-mirror photon mixing, then this could be detected in dark matter direct detection experiments such as DAMA/NaI and its successor DAMA/LIBRA. In fact, it is one of the few dark matter candidates which can explain the positive DAMA/NaI dark matter signal whilst still being consistent with the null results of other dark matter experiments. Mirror matter may also be detected in electromagnetic field penetration experiments and there would also be consequences for planetary science and astrophysics.
Mirror matter could also be responsible for the GZK puzzle. Topological defects in the mirror sector could produce mirror neutrinos which can oscillate to ordinary neutrinos. Another possible way to evade the GZK bound is via neutron-mirror neutron oscillations.
Read more about this topic: Mirror Photon
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