Eur. Phys. J. C (2017) 77: 458
https://doi.org/10.1140/epjc/s10052-017-5029-9

Regular Article - Theoretical Physics

Integrability from point symmetries in a family of cosmological Horndeski Lagrangians

¹ Instituto de Ciencias Físicas y Matemáticas, Universidad Austral de Chile, Valdivia, Chile
² Institute of Systems Science, Durban University of Technology, PO Box 1334, Durban, 4000, Republic of South Africa

^* e-mail: anpaliat@phys.uoa.gr

Received: 27 February 2017
Accepted: 28 June 2017
Published online: 10 July 2017

Abstract

For a family of Horndeski theories, formulated in terms of a generalized Galileon model, we study the integrability of the field equations in a Friedmann–Lemaître–Robertson–Walker space-time. We are interested in point transformations which leave invariant the field equations. Noether’s theorem is applied to determine the conservation laws for a family of models that belong to the same general class. The cosmological scenarios with or without an extra perfect fluid with constant equation of state parameter are the two important cases of our study. The de Sitter universe and ideal gas solutions are derived by using the invariant functions of the symmetry generators as a demonstration of our result. Furthermore, we discuss the connection of the different models under conformal transformations while we show that when the Horndeski theory reduces to a canonical field the same holds for the conformal equivalent theory. Finally, we discuss how singular solutions provides nonsingular universes in a different frame and vice versa.