Imperial College London
Portrait Picture

Claudia de Rham

Faculty of Natural Sciences, Department of Physics

Professor of Theoretical Physics
 
 
 
//

Contact

 

c.de-rham CV

 
 
//

Location

 

H506Huxley BuildingSouth Kensington Campus

//

Summary

 

Publications

Citation

BibTex format

@article{de:2016:06/041,
author = {de, Rham C and Matas, A},
doi = {06/041},
journal = {Journal of Cosmology and Astroparticle Physics},
title = {Ostrogradsky in theories with multiple fields},
url = {http://dx.doi.org/10.1088/1475-7516/2016/06/041},
volume = {2016},
year = {2016}
}
Download

RIS format (EndNote, RefMan)

TY  - JOUR
AB  - We review how the (absence of) Ostrogradsky instability manifests itself in theories with multiple fields. It has recently been appreciated that when multiple fields are present, the existence of higher derivatives may not automatically imply the existence of ghosts. We discuss the connection with gravitational theories like massive gravity and beyond Horndeski which manifest higher derivatives in some formulations and yet are free of Ostrogradsky ghost. We also examine an interesting new class of Extended Scalar-Tensor Theories of gravity which has been recently proposed. We show that for a subclass of these theories, the tensor modes are either not dynamical or are infinitely strongly coupled. Among the remaining theories for which the tensor modes are well-defined one counts one new model that is not field-redefinable to Horndeski via a conformal and disformal transformation but that does require the vacuum to break Lorentz invariance. We discuss the implications for the effective field theory of dark energy and the stability of the theory. In particular we find that if we restrict ourselves to the Extended Scalar-Tensor class of theories for which the tensors are well-behaved and the scalar is free from gradient or ghost instabilities on FLRW then we recover Horndeski up to field redefinitions.
AU  - de,Rham C
AU  - Matas,A
DO  - 06/041
PY  - 2016///
SN  - 1475-7516
TI  - Ostrogradsky in theories with multiple fields
T2  - Journal of Cosmology and Astroparticle Physics
UR  - http://dx.doi.org/10.1088/1475-7516/2016/06/041
UR  - http://hdl.handle.net/10044/1/42755
VL  - 2016
ER  -
Download