Inflation from Minkowski space

Abstract

We propose a class of scalar models that, once coupled to gravity, lead to cosmologies that smoothly and stably connect an inflationary quasi-de Sitter universe to a low, or even zero-curvature, maximally symmetric spacetime in the asymptotic past, strongly violating the null energy condition (Ḣ H 2 ) at intermediate times. The models are deformations of the conformal galileon lagrangian and are therefore based on symmetries, both exact and approximate, that ensure the quantum robustness of the whole picture. The resulting cosmological backgrounds can be viewed as regularized extensions of the galilean genesis scenario, or, equivalently, as 'early-time-complete' realizations of inflation. The late-time inflationary dynamics possesses phenomenologically interesting properties: it can produce a large tensor-to-scalar ratio within the regime of validity of the effective field theory and can lead to sizeable equilateral nongaussianities.

The Effective Field Theory of nonsingular cosmology

“…What is the effective theory of nonsingular cosmology is a significant issue. It is interesting to notice that some spatial covariant operators also help to remove the gradient instability [7,9,10].…”

“…As the operator (R (3) ) 2 has been applied to the nonsingular cosmology in [9], here we'd like to take the following nonsingular model…”

“…However, the inflation still suffers from the cosmological singularity problem [1,2], unless it was preceded by a bounce [3][4][5][6][7] or a Genesis phase [8][9][10]. It is exciting to study classical nonsingular cosmology, such as bounce universe models [11,12], Genesis models [13][14][15], slow expansion models [16][17][18][19], since we might get classical nonsingular cosmology without begging the details of the unknown UV-complete gravity theory.…”

“…[13,17,18,27,28]. However, it seems quite difficult to avoid the gradient instability problem, which indicates a negative sound speed squared [7,9,29,30] and thus leads to an exponential growth of the perturbation [31,32].…”

G-bounce inflation: towards nonsingular inflation cosmology with galileon field

“…However, the nasty instability might be avoided if we expect some additional corrections in the high energy region such as around the bounce [66]. For example, we phenomenologically assume that there is an additional term in the action of gravity such as:…”