Properties of GOG Pair fluctuations It reduce to bcs mean field at t=o It generates pseudogap at finite t a The superfluid transition is a continuous transition Consistency requires a gauge invariant linear response theoryProperties of G0G Pair fluctuations ◼ It reduce to BCS mean field at T=0 ◼ It generates pseudogap at finite T ◼ The superfluid transition is a continuous transition. ◼ Consistency requires a gauge invariant linear response theory