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Cosmological tests of coupled Galileons

Brax, Philippe; Burrage, Clare; Davis, Anne-Christine; Gubitosi, Giulia

Authors

Philippe Brax

Anne-Christine Davis

Giulia Gubitosi



Abstract

We investigate the cosmological properties of Galileon models which admit Minkowski space as a stable solution in vacuum. This is motivated by stable, positive tension brane world constructions that give rise to Galileons. We include both conformal and disformal couplings to matter and focus on constraints on the theory that arise because of these couplings. The disformal coupling to baryonic matter is extremely constrained by astrophysical and particle physics effects. The disformal coupling to photons induces a cosmological variation of the speed of light and therefore distorsions of the Cosmic Microwave Background spectrum which are known to be very small. The conformal coupling to baryons leads to a variation of particle masses since Big Bang Nucleosynthesis which is also tightly constrained. We consider the background cosmology of Galileon models coupled to Cold Dark Matter (CDM), photons and baryons and impose that the speed of light and particle masses respect the observational bounds on cosmological time scales. We find that requiring that the equation of state for the Galileon models must be close to -1 now restricts severely their parameter space and can only be achieved with a combination of the conformal and disformal couplings. This leads to large variations of particle masses and the speed of light which are not compatible with observations. As a result, we find that cosmological Galileon models are viable dark energy theories coupled to dark matter but their couplings, both disformal and conformal, to baryons and photons must be heavily suppressed making them only sensitive to CDM.

Journal Article Type Article
Publication Date Mar 13, 2015
Journal Journal of Cosmology and Astroparticle Physics
Electronic ISSN 1475-7516
Publisher IOP Publishing
Peer Reviewed Peer Reviewed
Volume 15
Issue 3
Article Number 028
APA6 Citation Brax, P., Burrage, C., Davis, A., & Gubitosi, G. (2015). Cosmological tests of coupled Galileons. Journal of Cosmology and Astroparticle Physics, 15(3), https://doi.org/10.1088/1475-7516/2015/03/028
DOI https://doi.org/10.1088/1475-7516/2015/03/028
Publisher URL http://iopscience.iop.org/article/10.1088/1475-7516/2015/03/028/meta
Copyright Statement Copyright information regarding this work can be found at the following address: http://eprints.nottingh.../end_user_agreement.pdf

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Copyright Statement
Copyright information regarding this work can be found at the following address: http://eprints.nottingham.ac.uk/end_user_agreement.pdf





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