Neutron - mirror neutron mixing and neutron stars
Abstract
The oscillation of neutrons n into mirror neutrons n', their mass degenerate partners from dark mirror sector, can have interesting implications for neutron stars: an ordinary neutron star could gradually transform into a mixed star consisting in part of mirror dark matter. Mixed stars can be detectable as twin partners of ordinary neutron stars: namely, there can exist compact stars with the same masses but having different radii. For a given equation of state (identical between the ordinary and mirror components), the mass and radius of a mixed star depend on the proportion between the ordinary and mirror components in its interior which in turn depends on its age. If 50 \% - 50\% proportion between two fractions can be reached asymptotically in time, then the maximum mass of such "maximally mixed stars" should be 2 times smaller than that of ordinary neutron star while the stars exceeding a critical mass value M maxNS/2 should collapse in black holes after certain time. We evaluate the evolution time and discuss the implications of n-n' transition for the pulsar observations as well as for the gravitational waves from the neutron star mergers and associated electromagnetic signals.