Abstract
In this work, we extend the framework analyzed in some previous work and study in depth the parameter space of the model, obtaining detailed outcomes not revealed in the previous work. We assume that some of the dark matter of the Universe is composed by low-scale mirror dark matter, which is allowed to interact only gravitationally with the Standard Model world. By varying the Yukawa couplings in the low-scale mirror dark matter world, the mirror world can experience dark cosmological phase transitions, which can be first order or second order. We study the observable effects of the dark phase transitions in our Standard Model world, and as we evince, the second-order phase transitions can lead to a deformation of the total background equation of state for temperatures of the order [Formula: see text]GeV, but have no other effect on our world. On the contrary, first-order phase transitions can generate a stochastic gravitational wave background that could be detected by future gravitational wave experiments. In addition, we examine when the mirror world has a large abundance and also whether it contains atoms among the dark matter particles. The latter two features depend mainly on the values of the Yukawa couplings and the mirror Higgs self-coupling.