Journal Article Multi-disformal invariance of non-linear primordial perturbations

Watanabe, Yuki  ,  Naruko, Atsushi  ,  Sasaki, Misao

111 ( 3 ) 2015-08-07 , IOP Publishing
ISSN:0295-5075
NCID:AA10668127
Description
We study disformal transformations of the metric in the cosmological context. We first consider the disformal transformation generated by a scalar field phgr and show that the curvature and tensor perturbations on the uniform phgr slicing, on which the scalar field is homogeneous, are non-linearly invariant under the disformal transformation. Then we discuss the transformation properties of the evolution equations for the curvature and tensor perturbations at full non-linear order in the context of spatial gradient expansion as well as at linear order. In particular, we show that the transformation can be described in two different ways: one that clearly shows the physical invariance and the other that shows an apparent change of the causal structure. Finally we consider a new type of disformal transformation in which a multi-component scalar field comes into play, which we call a "multi-disformal transformation". We show that the curvature and tensor perturbations are invariant at linear order, and also at non-linear order, provided that the system has reached the adiabatic limit.
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http://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/202018/1/0295-5075_111_39002.pdf

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