Gaugetransformation properties of cosmological observables and its application to the lightcone average
Abstract
Theoretical descriptions of observable quantities in cosmological perturbation theory should be independent of coordinate systems. This statement is often referred to as gaugeinvariance of observable quantities, and the sanity of their theoretical description is verified by checking its gaugeinvariance. We argue that cosmological observables are invariant scalars under diffeomorphisms and their theoretical description is gaugeinvariant, only at linear order in perturbations. Beyond linear order, they are usually not gaugeinvariant, and we provide the general law for the gaugetransformation that the perturbation part of an observable does obey. We apply this finding to derive the secondorder expression for the observational lightcone average in cosmology and demonstrate that our expression is indeed invariant under diffeomorphisms.
 Authors:
 Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zürich, Winterthurerstrasse 190, CH8057, Zürich (Switzerland)
 Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Quai E. Ansermet 24, CH1211 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, Email: jyoo@physik.uzh.ch, Email: ruth.durrer@unige.ch. Gaugetransformation properties of cosmological observables and its application to the lightcone average. United States: N. p., 2017.
Web. doi:10.1088/14757516/2017/09/016.
Yoo, Jaiyul, & Durrer, Ruth, Email: jyoo@physik.uzh.ch, Email: ruth.durrer@unige.ch. Gaugetransformation properties of cosmological observables and its application to the lightcone average. United States. doi:10.1088/14757516/2017/09/016.
Yoo, Jaiyul, and Durrer, Ruth, Email: jyoo@physik.uzh.ch, Email: ruth.durrer@unige.ch. 2017.
"Gaugetransformation properties of cosmological observables and its application to the lightcone average". United States.
doi:10.1088/14757516/2017/09/016.
@article{osti_22667694,
title = {Gaugetransformation properties of cosmological observables and its application to the lightcone average},
author = {Yoo, Jaiyul and Durrer, Ruth, Email: jyoo@physik.uzh.ch, Email: 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 gaugeinvariance of observable quantities, and the sanity of their theoretical description is verified by checking its gaugeinvariance. We argue that cosmological observables are invariant scalars under diffeomorphisms and their theoretical description is gaugeinvariant, only at linear order in perturbations. Beyond linear order, they are usually not gaugeinvariant, and we provide the general law for the gaugetransformation that the perturbation part of an observable does obey. We apply this finding to derive the secondorder expression for the observational lightcone average in cosmology and demonstrate that our expression is indeed invariant under diffeomorphisms.},
doi = {10.1088/14757516/2017/09/016},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 09,
volume = 2017,
place = {United States},
year = 2017,
month = 9
}

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