Authors: Vesić, Nenad 
Dimitrijević, Dragoljub
Đorđević, Goran
Milošević, Milan
Stojanović, Marko
Affiliations: Mathematics 
Mathematical Institute of the Serbian Academy of Sciences and Arts 
Title: On a gauge invariant variable for scalar perturbations during inflation
First page: 59
Related Publication(s): Book of Abstracts
Conference: The 11th International Conference of the Balkan Physical Union
Issue Date: 2022
Rank: M34
We discuss cosmological perturbations of the scalar type in the spatially flat FRWL
background during inflation. There are five independent scalar perturbations. Four
of them are perturbations of the FRWL metric and the fifth one represents perturba-
tions of a scalar field. As usual, a scalar field is used to describe dominant (perfect)
cosmological fluid responsible for inflation [1].
These five scalar perturbations are not gauge invariant, i.e. their values strongly de-
pend on coordinate system we use and are not physical. In order to obtain physical
quantities, gauge invariant variables are introduced. Their values will not depend
on a choice of coordinate system we use and will not change under general coordi-
nate transformations.
Frequently used gauge invariant scalar perturbations in the literature are two
Bardeen’s potentials, the gauge invariant perturbations of a scalar field and the
Mukhanov-Sasaki variable [2,3,4]. The main idea is to construct a general gauge
invariant variable, that will contain all four mentioned gauge variables. It can be
done by looking at a set of expressions defining explained in details in this work. At
the end, we discuss about dynamical equation and its solution for a general gauge
invariant variable
Publisher: SANU; Prirodno matematički fakultet Univerziteta u Nišu

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