The effective field theory of nonsingular cosmology: II

Abstract

Based on the effective field theory (EFT) of cosmological perturbations, we explicitly clarify the pathology in nonsingular cubic Galileon models and show how to cure it in EFT with new insights into this issue. With the least set of EFT operators that are capable to avoid instabilities in nonsingular cosmologies, we construct a nonsingular model dubbed the Genesis-inflation model, in which a slowly expanding phase (namely, Genesis) with increasing energy density is followed by slow-roll inflation. The spectrum of the primordial perturbation may be simulated numerically, which shows itself a large-scale cutoff, as the large-scale anomalies in CMB might be a hint for.

A covariant Lagrangian for stable nonsingular bounce

“…The P (φ, X) nonsingular bounce model could be ghostfree [31,37], but suffers the problem of c 2 s < 0, which can not be dispelled by using the Galileon interaction ∼ φ [6][7][8][9]. Actually, in [10,38], it is observed that the Galileon interaction only moves the period of c 2 s < 0 to the outside of the bounce phase, but can not remove it, see also earlier [39]. Thus it could be imagined that the quadratic order of the second order derivative of φ, i.e., φ µν φ µν , ( φ) 2 , φ µ φ µρ φ ρν φ ν and ( φ)φ µ φ µν φ ν , might play crucial roles in stable nonsingular bounce model.…”

“…Recently, this observation has been proved, up to the cubic Galileon theory [6] and the Horndeski theory [7]. Based on the effective field theory (EFT) of nonsingular cosmologies [8][9][10], this No-go result has been more clearly illustrated. It is found that the stable nonsingular cosmological models can be implemented only in the theories beyond cubic Galileon, (see also [11,12]).…”

“…[8,10]. It should be mentioned that if f 1 = 0, we have c 2 s ∼ −Ḣ < 0 around the bounce point, thus S δg 00 R (3) is needed to contribute f 1 .…”

“…It should be mentioned that if f 1 = 0, we have c 2 s ∼ −Ḣ < 0 around the bounce point, thus S δg 00 R (3) is needed to contribute f 1 . Here, we always could set c 2 s ∼ O(1) with a suitable f 1 (φ) (see also [10]) which satisfies…”

Higher order derivative coupling to gravity and its cosmological implications

“…Recently, the EFT has also been applied to the nonsingular cosmologies [20][21] [22]. It was found first in Refs.…”