Abstract. Adiabatic modes (ADMs) play an essential role in derivation of soft theorems in Cosmology. They also give us non-trivial solutions to the Einstein perturbed equations that are almost independent from the matter content of the universe. They are defined as the physical perturbations (on the top of a fixed FRW universe), that can be locally removed by a local coordinate transformation.
In this work we systematically construct the adiabatic modes and find new time-dependent ones. In the light of a new time dependent ADM for graviton, we show that alternative theories to inflation enjoy asymptotic symmetries associated with soft gravitons. We point out adiabaticity of vector perturbations and mention the relevance of this finding to primordial magnetogenesis.
New ADMs, possess interesting features. In particular, they can be either mixed or pure in terms of scalar-vector-tensor decomposition. The long mode of the tensor perturbation is able to have quantum behavior even on large scales. Also, we figure out that some ADMs can not be monochromatic but instead, they will be continued to spherical waves.
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