The speed of Galileon gravity
We analyse the speed of gravitational waves in coupled Galileon models with an equation of state ωphgr=−1 now and a ghost-free Minkowski limit. We find that the gravitational waves propagate much faster than the speed of light unless these models are small perturbations of cubic Galileons and the Ga...
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| Format: | Article |
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IOPScience
2016
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| Online Access: | https://eprints.nottingham.ac.uk/42092/ |
| _version_ | 1848796416688783360 |
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| author | Brax, Philippe Burrage, Clare Davis, Anne-Christine |
| author_facet | Brax, Philippe Burrage, Clare Davis, Anne-Christine |
| author_sort | Brax, Philippe |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | We analyse the speed of gravitational waves in coupled Galileon models with an equation of state ωphgr=−1 now and a ghost-free Minkowski limit. We find that the gravitational waves propagate much faster than the speed of light unless these models are small perturbations of cubic Galileons and the Galileon energy density is sub-dominant to a dominant cosmological constant. In this case, the binary pulsar bounds on the speed of gravitational waves can be satisfied and the equation of state can be close to -1 when the coupling to matter and the coefficient of the cubic term of the Galileon Lagrangian are related. This severely restricts the allowed cosmological behaviour of Galileon models and we are forced to conclude that Galileons with a stable Minkowski limit cannot account for the observed acceleration of the expansion of the universe on their own. Moreover any sub-dominant Galileon component of our universe must be dominated by the cubic term. For such models with gravitons propagating faster than the speed of light, the gravitons become potentially unstable and could decay into photon pairs. They could also emit photons by Cerenkov radiation. We show that the decay rate of such speedy gravitons into photons and the Cerenkov radiation are in fact negligible. Moreover the time delay between the gravitational signal and light emitted by explosive astrophysical events could serve as a confirmation that a modification of gravity acts on the largest scales of the Universe. |
| first_indexed | 2025-11-14T19:47:38Z |
| format | Article |
| id | nottingham-42092 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| last_indexed | 2025-11-14T19:47:38Z |
| publishDate | 2016 |
| publisher | IOPScience |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-420922020-05-04T17:42:48Z https://eprints.nottingham.ac.uk/42092/ The speed of Galileon gravity Brax, Philippe Burrage, Clare Davis, Anne-Christine We analyse the speed of gravitational waves in coupled Galileon models with an equation of state ωphgr=−1 now and a ghost-free Minkowski limit. We find that the gravitational waves propagate much faster than the speed of light unless these models are small perturbations of cubic Galileons and the Galileon energy density is sub-dominant to a dominant cosmological constant. In this case, the binary pulsar bounds on the speed of gravitational waves can be satisfied and the equation of state can be close to -1 when the coupling to matter and the coefficient of the cubic term of the Galileon Lagrangian are related. This severely restricts the allowed cosmological behaviour of Galileon models and we are forced to conclude that Galileons with a stable Minkowski limit cannot account for the observed acceleration of the expansion of the universe on their own. Moreover any sub-dominant Galileon component of our universe must be dominated by the cubic term. For such models with gravitons propagating faster than the speed of light, the gravitons become potentially unstable and could decay into photon pairs. They could also emit photons by Cerenkov radiation. We show that the decay rate of such speedy gravitons into photons and the Cerenkov radiation are in fact negligible. Moreover the time delay between the gravitational signal and light emitted by explosive astrophysical events could serve as a confirmation that a modification of gravity acts on the largest scales of the Universe. IOPScience 2016-03-04 Article PeerReviewed Brax, Philippe, Burrage, Clare and Davis, Anne-Christine (2016) The speed of Galileon gravity. Journal of Cosmology and Astroparticle Physics, 2016 (03). 004/1-004/17. ISSN 1475-7516 dark energy theory gravitational waves / theory modified gravity http://iopscience.iop.org/article/10.1088/1475-7516/2016/03/004/meta doi:10.1088/1475-7516/2016/03/004 doi:10.1088/1475-7516/2016/03/004 |
| spellingShingle | dark energy theory gravitational waves / theory modified gravity Brax, Philippe Burrage, Clare Davis, Anne-Christine The speed of Galileon gravity |
| title | The speed of Galileon gravity |
| title_full | The speed of Galileon gravity |
| title_fullStr | The speed of Galileon gravity |
| title_full_unstemmed | The speed of Galileon gravity |
| title_short | The speed of Galileon gravity |
| title_sort | speed of galileon gravity |
| topic | dark energy theory gravitational waves / theory modified gravity |
| url | https://eprints.nottingham.ac.uk/42092/ https://eprints.nottingham.ac.uk/42092/ https://eprints.nottingham.ac.uk/42092/ |