AT4 - Massive gravity, Horndeski theory and other "ghost-free" models of modified gravity |
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Speaker |
Suvorov, Arthur |
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Coauthors |
Suvorov, Arthur G.; Melatos, Andrew |
| Talk Title |
Nonlinear tachyons in modified gravity |
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Abstract |
In the quest for finding a quantum theory of gravity, many models have been proposed which classically resemble general relativity but with a modified action. In general relativity, gravitational wave-fronts trace out null hypersurfaces. In some modified theories, linearised gravitational waves satisfy dispersion relationships and propagate at speeds different than light. In particular, theories which predict tachyonic waves or ghosts are often excluded on physical grounds, providing a way to whittle down the pool of viable extensions of GR. We show that some theories which avoid linear instabilities may still admit exact, non-linear solutions which describe superluminal gravitational waves. These theories may then need to be discarded if causality is to be maintained. Some astrophysical consequences are discussed. |
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