A Shadow Matter Universe

The cosmological and astrophysical implications of a shadow matter model which could also have interesting experimental consequences are examined. The model has identical microphysics for both the ordinary and shadow worlds but requires a macroscopic asymmetry from nucleosynthesis constraints. It is proposed that this macroscopic asymmetry can be generated at the quark-hadron phase transition. PACS number(s): 98.80.Cq, 12.15.Cc email: lew%[email protected] From time to time there have been some speculation about the existence of “shadow matter” in the Universe and its consequences [1, 2, 3]. This shadow matter is another form of matter which is thought to interact with ordinary matter via gravity or via interactions of comparable strength to gravity. Some of the astrophysical and cosmological implications of generic shadow matter models have been studied in Ref.[2]. In this paper the astrophysical and cosmological consequences of a particular realization of the shadow matter scenario, which may also have interesting collider physics, will be discussed. The construction of a shadow matter model is quite straightforward. Consider the Lagrangian L = L1 + L2 (1) where L1,2 describes the physics of the ordinary and shadow worlds respectively. If the requirement that the microphysics of the two worlds be identical is imposed then there exists a discrete symmetry such that L1 ←→ L2. (2) Let G1,2 be the gauge group of L1,2 where G1 and G2 are isomorphic and interchange under the discrete symmetry. The gauge group of L is then G1⊗G2 with the particle content of the ordinary and mirror worlds described by the representations (R, 1) ⊕ (1, R). For example, the gauge group could be E8 ⊗ E8 as motivated by superstring theories. The discrete symmetry between the ordinary and shadow worlds may or may not survive at low energies. In the following the gauge group, G1,2, is taken to be the Minimal Standard Model (MSM) which means that the particle content of each sector contains no more than one Higgs doublet and no right-handed neutrinos. This model has been discussed previously (see Ref.[3]) with the motivation that the discrete symmetry between the two sectors be interpreted as an improper spacetime symmetry, e.g. parity. It is perhaps interesting to note that this discrete symmetry remain intact at low energies after gauge symmetry breaking. What is of more interest is that this model could have testable consequences at future collider experiments. This comes from the non-gravitational interactions caused by the mixing of the two sectors, viz., the mixing of the