Mirror matter

Abstract: A "parallel world" with all of the standard particles, which primarily interacts gravitationally with our world, can be motivated via a symmetry principle designed to make a Lagrangian $\mathrm{CP}$ symmetric, while maintaining a $\mathrm{CP}$ asymmetry in the observable world Such a symmetry is easily accommodated in grand unified theory models, and may also arise in superstring theories The cosmological abundance of mirror particles is investigated after a period of chaotic inflation and subsequent reheating Contrary to previous studies, I find that mirror and ordinary abundances may naturally be similar at the present epoch, and that mirror baryons can provide the closure density without violating nucleosynthesis constraints

Abstract: A simple way to accommodate dark matter is to postulate the existence of a hidden sector. That is, a set of new particles and forces interacting with the known particles predominantly via gravity. In general this leads to a large set of unknown parameters, however if the hidden sector is an exact copy of the standard model sector, then an enhanced symmetry arises. This symmetry, which can be interpreted as space-time parity, connects each ordinary particle ($e, \ u, \ p, \ n, \ \gamma, ....)$ with a mirror partner ($e', \ u', \ p', \ n', \ \gamma', ...)$. If this symmetry is completely unbroken, then the mirror particles are degenerate with their ordinary particle counterparts, and would interact amongst themselves with exactly the same dynamics that govern ordinary particle interactions. The only new interaction postulated is photon - mirror photon kinetic mixing, whose strength $\epsilon$, is the sole new fundamental (Lagrangian) parameter relevant for astrophysics and cosmology. It turns out that such a theory, with suitably chosen initial conditions effective in the very early Universe, can provide an adequate description of dark matter phenomena provided that $\epsilon \sim 10^{-9}$. This review focuses on three main developments of this mirror dark matter theory during the last decade: Early universe cosmology, galaxy structure and the application to direct detection experiments.

Abstract: We briefly review the concept of a parallel 'mirror' world which has the same particle physics as the observable world and couples to the latter by gravity and perhaps other very weak forces. The nucleosynthesis bounds demand that the mirror world should have a smaller temperature than the ordinary one. By this reason its evolution should substantially deviate from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. In particular, we show that in the context of certain baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one. Moreover, we show that mirror baryons could naturally constitute the dominant dark matter component of the Universe, and discuss its cosmological implications.