Quark matter and cosmology

The possible implications of the quark-hadron transition for cosmology are explored. Possible signatures are discussed such as dark matter candidates like strange nuggets or planetary mass black holes. Much discussion is devoted to the possible role of the transition for cosmological nucleosynthesis. It is emphasized that even an optimized first order phase transition will not significantly alter the nucleosynthesis constraints on the cosmological baryon density nor on neutrino counting. However, it is noted that Be and B observations in old stars may eventually be able to be a signature of a cosmologically significant quark-hadron transition. It is pointed out that spallation cannot produce a B Be ratio below 7.6. A supporting signature for cosmological would be Be and B ratios to oxygen that greatly exceed galactic values. At present, all data is consistent with a spallagenic origin.