Abstract : Theories with higher order time derivatives generically suffer from ghost-like instabilities, known as Ostrogradski instabilities. This fate can be avoided by considering degenerate'' Lagrangians, whose kinetic matrix cannot be inverted, thus leading to constraints between canonical variables and a reduced number of physical degrees of freedom. In this work, we derive in a systematic way the degeneracy conditions for scalar-tensor theories that depend quadratically on second order derivatives of a scalar field. We thus obtain a classification of all degenerate theories within this class of scalar-tensor theories. The quartic Horndeski Lagrangian and its extension beyond Horndeski belong to these degenerate cases. We also identify new families of scalar-tensor theories with the property that they are degenerate despite the nondegeneracy of the purely scalar part of their Lagrangian.
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Article dans une revue
JCAP, 2016, 02 (02), pp.034. 〈10.1088/1475-7516/2016/02/034〉
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https://hal.archives-ouvertes.fr/hal-01554319
Contributeur : Inspire Hep <>
Soumis le : lundi 3 juillet 2017 - 17:50:25
Dernière modification le : mercredi 20 mars 2019 - 11:28:06

### Citation

David Langlois, Karim Noui. Degenerate higher derivative theories beyond Horndeski: evading the Ostrogradski instability. JCAP, 2016, 02 (02), pp.034. 〈10.1088/1475-7516/2016/02/034〉. 〈hal-01554319〉

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