Thursday 14 December 2017
to 14:15 at
Sadra Jazayeri (Institute for Theoretical Physics, Utrecht & IPM, Tehran)
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. Moreover, we
figure out that some ADMs can not be monochromatic but instead they will be
continued into spherical waves.