Unrivaled Quantum Vacuum in the Primordial Universe
In a primordial universe pre(post)-inflationary era , there could be phases of early universe made of cold gas baryons, radiation and early post inflationary cosmological constant. I showed that in the baryonic epoch, the quantum vacuum is unique. By using the standard quantization scheme for a massive minimally coupled scalar field with maximal conformal symmetry in the classical spacetime, I demonstrated that the scalar modes had an effective mass $m_{eff}^2\approx 0$ (or $m_{eff}^2\approx constant$). This argument validated when the conformal time $\eta$ kept so close to the inflation ending time $\eta=\eta_c$. The energy density of the baryonic matter diverged at the inflation border and vanishes at the late time future. Furthermore I argued that at very early accelerating epoch when the radiation was the dominant part in the close competition with the early time cosmological constant, fine tuned mass of the scalar field $m\propto \sqrt{\Lambda}$ also provided a unique quantum vacuum. The reason is that the effective mass eventually is vanished. A remarkable observation was that all the other possible vacuum states "squeezed" eternally.