Thermal non-Gaussianity in Near-Milne universe

The thermal non-Gaussianity in Near-Milne universe is investigated in this Letter. Through classifying thermal fluctuations into two types, one characterized by a phase transition and the other without phase transition, we show that for fluctuations undergoing a phase transition, the non-Gaussianity depends linearly on k, but in non-phase transition case it is proportional to k−3γ, γ>0. Moreover, if the phase transition scenario is similar to that in holographic cosmology, we find that the non-Gaussianity fNLequil can reach O(1) or larger than O(1) by fine tuning of the equation of state ωC. Especially at the limit of ωC→−5/3, the non-Gaussianity can be very large. On the other hand, for non-phase transition case, the non-Gaussianity estimator fNLequil is approximately fNLequil≃5/108 when the energy is sub-extensive, especially when γ→0+. However, when γ→4, large non-Gaussianity can be obtained.