Mirror Neutrinos and the Early Universe

The Exact Parity Model (EPM) sees the ordinary particle sector reflected, darkly, in a mirror sector. It is a phenomenologically acceptable extension of the Standard Model (SM) of particle physics which displays invariance under Improper Lorentz Transformations (Parity and Time-Reversal invariance). Remarkably, the invariance or otherwise of microphysical laws and the physical vacuum under the full Lorentz Group is still an open question, despite the V −A character of weak interactions. Almost as a byproduct, the EPM furnishes a unified solution to the solar and atmospheric neutrino problems; it can also easily accomodate the LSND result. In this talk I will review the resolution of the neutrino anomalies within the EPM. I will also discuss how the oscillation driven relic neutrino asymmetry amplification mechanism ensures consistency with Big Bang Nucleosynthesis (BBN). Consider your favourite parity-violating Lagrangian L(ψ) which is invariant under gauge group G. Here I take L to be the Lagrangian of the minimal SM augmented by right-handed neutrinos and nonzero neutrino masses. I also go to the region of parameter space where the see-saw mechanism operates, so the ordinary left-handed neutrinos are naturally very light Majorana particles. For every ordinary field ψ, introduce a mirror or parity partner ψ. All ordinary fields are parity-doubled, including gauge and Higgs bosons. The new Lagrangian