Bounce and cyclic cosmology in weakly broken Galileon theories

Abstract

Abstract:We investigate the bounce and cyclicity realization in the framework of weakly broken galileon theories. We study bouncing and cyclic solutions at the background level, reconstructing the potential and the galileon functions that can give rise to a given scale factor, and presenting analytical expressions for the bounce requirements. We proceed to a detailed investigation of the perturbations, which after crossing the bouncing point give rise to various observables, such as the scalar and tensor spectral indices and the tensor-toscalar ratio. Although the scenario at hand shares the disadvantage of all bouncing models, namely that it provides a large tensor-to-scalar ratio, introducing an additional light scalar significantly reduces it through the kinetic amplification of the isocurvature fluctuations.

A covariant Lagrangian for stable nonsingular bounce

“…Our work actually offers a concise way to the fully stable nonsingular cosmologies. See also [40][41][42][43][44][45][46][47][48] for other interesting studies.…”

Cosmological implications of a shift symmetric Galileon field

“…Thus given a suitable scale factor describing evolution of our universe we can use the Friedmann equations to determine the structure of the potential. In a recent work using the reconstruction method the authors have tried to demonstrate the structure of the functions G 2 , G 3 in weakly broken Galileon theories for either a bouncing or cyclic cosmology, here we apply it to the late time acceleration [47,53].…”

“…However due to complicated nature of the field equations it is difficult to derive the potential from first principles, a tedious root would be to guess the form of the potential by inspection. Nevertheless, there exists an alternative and more reliable root to arrive at the potential, namely the reconstruction scheme [48][49][50][51][52][53]. In the following we will try to apply the reconstruction method, ultimately obtaining a potential leading to late time cosmic acceleration.…”

Stable singularity-free cosmological solutions in nonprojectable Hořava-Lifshitz gravity

“…Since the no-go theorem is established based on the Horndeski theory, in other words, the most generalized scalartensor theory whose equation of motion is up to second order [20], one may consider it is difficult to find stable cosmological solutions without a singularity. However, * Electronic address: m.fukushima"at"aoni.waseda.jp † Electronic address: y"underscore"misonou"at"moegi.waseda.jp ‡ Electronic address: miyashita"at"gravity.phys.waseda.ac.jp § Electronic address: s.seiga"at"gravity.phys.waseda.ac.jp certain loopholes of the no-go theorem are known [21][22][23][24]. One example of such loophole is to consider a Lorenz violating gravitational theory.…”