Abstract
We discuss the stability of the classical bouncing solutions in the general Horndeski theory and beyond Horndeski theory. We restate the no-go theorem, showing that in the general Horndeski theory there are no spatially flat non-singular cosmological solutions which are stable during entire evolution. We show the way to evade the no-go in beyond Horndeski theory and give two specific examples of bouncing solutions, whose asymptotic past and future or both are described by General Relativity (GR) with a conventional massless scalar field. Both solutions are free of any pathologies at all times.
Highlights
Cosmological bounce is one of the attractive ways to avoid the initial singularity implied by the conventional Big Bang theory
We restate the no-go theorem, showing that in the general Horndeski theory there are no spatially flat non-singular cosmological solutions which are stable during entire evolution
We show the way to evade the no-go in beyond Horndeski theory and give two specific examples of bouncing solutions, whose asymptotic past and future or both are described by General Relativity (GR) with a conventional massless scalar field
Summary
Cosmological bounce is one of the attractive ways to avoid the initial singularity implied by the conventional Big Bang theory. There are a lot of bouncing solutions suggested in the general Horndeski theory, which were free of obvious instabilities, but only during a certain period of time Γ-crossing denotes the moment when the denominator 2, which is present in the coefficients of the quadratic action for scalar perturbations in the unitary gauge, vanishes It is important to note that γ-crossing does not help with evading the no-go theorem in the general Horndeski theory, modulo the loophole mentioned above.
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