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Title: Gauge-transformation properties of cosmological observables and its application to the light-cone average

Abstract

Theoretical descriptions of observable quantities in cosmological perturbation theory should be independent of coordinate systems. This statement is often referred to as gauge-invariance of observable quantities, and the sanity of their theoretical description is verified by checking its gauge-invariance. We argue that cosmological observables are invariant scalars under diffeomorphisms and their theoretical description is gauge-invariant, only at linear order in perturbations. Beyond linear order, they are usually not gauge-invariant, and we provide the general law for the gauge-transformation that the perturbation part of an observable does obey. We apply this finding to derive the second-order expression for the observational light-cone average in cosmology and demonstrate that our expression is indeed invariant under diffeomorphisms.

Authors:
 [1];  [2]
  1. Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zürich, Winterthurerstrasse 190, CH-8057, Zürich (Switzerland)
  2. Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Quai E. Ansermet 24, CH-1211 Genève 4 (Switzerland)
Publication Date:
OSTI Identifier:
22667694
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 09; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMOLOGY; DISTURBANCES; GAUGE INVARIANCE; LIGHT CONE; PERTURBATION THEORY; VISIBLE RADIATION

Citation Formats

Yoo, Jaiyul, and Durrer, Ruth, E-mail: jyoo@physik.uzh.ch, E-mail: ruth.durrer@unige.ch. Gauge-transformation properties of cosmological observables and its application to the light-cone average. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/09/016.
Yoo, Jaiyul, & Durrer, Ruth, E-mail: jyoo@physik.uzh.ch, E-mail: ruth.durrer@unige.ch. Gauge-transformation properties of cosmological observables and its application to the light-cone average. United States. doi:10.1088/1475-7516/2017/09/016.
Yoo, Jaiyul, and Durrer, Ruth, E-mail: jyoo@physik.uzh.ch, E-mail: ruth.durrer@unige.ch. Fri . "Gauge-transformation properties of cosmological observables and its application to the light-cone average". United States. doi:10.1088/1475-7516/2017/09/016.
@article{osti_22667694,
title = {Gauge-transformation properties of cosmological observables and its application to the light-cone average},
author = {Yoo, Jaiyul and Durrer, Ruth, E-mail: jyoo@physik.uzh.ch, E-mail: ruth.durrer@unige.ch},
abstractNote = {Theoretical descriptions of observable quantities in cosmological perturbation theory should be independent of coordinate systems. This statement is often referred to as gauge-invariance of observable quantities, and the sanity of their theoretical description is verified by checking its gauge-invariance. We argue that cosmological observables are invariant scalars under diffeomorphisms and their theoretical description is gauge-invariant, only at linear order in perturbations. Beyond linear order, they are usually not gauge-invariant, and we provide the general law for the gauge-transformation that the perturbation part of an observable does obey. We apply this finding to derive the second-order expression for the observational light-cone average in cosmology and demonstrate that our expression is indeed invariant under diffeomorphisms.},
doi = {10.1088/1475-7516/2017/09/016},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 09,
volume = 2017,
place = {United States},
year = {Fri Sep 01 00:00:00 EDT 2017},
month = {Fri Sep 01 00:00:00 EDT 2017}
}