TY - JOUR
T1 - Cosmological stability in f(ϕ,G) gravity
AU - Tsujikawa, Shinji
N1 - Funding Information:
ST is supported by the Grant-in-Aid for Scientific Research Fund of the JSPS Nos. 19K03854 and 22K03642 .
Publisher Copyright:
© 2023 The Author(s)
PY - 2023/3/10
Y1 - 2023/3/10
N2 - In gravitational theories where a canonical scalar field ϕ with a potential V(ϕ) is coupled to a Gauss-Bonnet (GB) term G with the Lagrangian f(ϕ,G), we study the cosmological stability of tensor and scalar perturbations in the presence of a perfect fluid. We show that, in decelerating cosmological epochs with a positive tensor propagation speed squared, the existence of nonlinear functions of G in f always induces Laplacian instability of a dynamical scalar perturbation associated with the GB term. This is also the case for f(G) gravity, where the presence of nonlinear GB functions f(G) is not allowed during the radiation- and matter-dominated epochs. A linearly coupled GB term with ϕ of the form ξ(ϕ)G can be consistent with all the stability conditions, provided that the scalar-GB coupling is subdominant to the background cosmological dynamics.
AB - In gravitational theories where a canonical scalar field ϕ with a potential V(ϕ) is coupled to a Gauss-Bonnet (GB) term G with the Lagrangian f(ϕ,G), we study the cosmological stability of tensor and scalar perturbations in the presence of a perfect fluid. We show that, in decelerating cosmological epochs with a positive tensor propagation speed squared, the existence of nonlinear functions of G in f always induces Laplacian instability of a dynamical scalar perturbation associated with the GB term. This is also the case for f(G) gravity, where the presence of nonlinear GB functions f(G) is not allowed during the radiation- and matter-dominated epochs. A linearly coupled GB term with ϕ of the form ξ(ϕ)G can be consistent with all the stability conditions, provided that the scalar-GB coupling is subdominant to the background cosmological dynamics.
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U2 - 10.1016/j.physletb.2023.137751
DO - 10.1016/j.physletb.2023.137751
M3 - Article
AN - SCOPUS:85147684483
SN - 0370-2693
VL - 838
JO - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
JF - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
M1 - 137751
ER -