Late-Time Cosmological Phase Transitions

Abstract

It is shown that the potential galaxy formation and large-scale structure problems of (1) objects existing at high redshifts (Z ⋧ 5), (2) structures existing on scales of 100Mpc as well as velocity flows on such scales, and (3) minimal microwave anisotropies \( \frac{{\Delta T}}{T} \lesssim {10^{ - 5}} \) can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, siginificant random gaussian fluctuations and/or topological defects can form. Scale lengths of ∼100Mpc for large-scale structure as well as ∼1Mpc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition.