Toward evading the strong coupling problem in Horndeski genesis

Genesis within the Horndeski theory is one of possible scenarios for the start of the Universe. In this model, the absence of instabilities is obtained at the expense of the property that coefficients, serving as effective Planck masses, vanish in the asymptotics t → −∞, which signalizes the danger of strong coupling and inconsistency of the classical treatment. We investigate this problem in a specific model and extend the analysis of cubic action for perturbations (arXiv:2003.01202) to arbitrary order. Our study is based on power counting and dimensional analysis of the higher order terms. We derive the latter, find characteristic strong coupling energy scales and obtain the conditions for the validity of the classical description. Curiously, we find that the strongest condition is the same as that obtained in already examined cubic case.

Section: Introductionmentioning

confidence: 89%

Section: Jhep12(2020)107mentioning

confidence: 99%

Section: Jhep12(2020)107mentioning

confidence: 99%

Section: Jhep12(2020)107mentioning

confidence: 99%

“…1 In refs. [29,30], the strong coupling problem in the model of ref. [19] has been addressed at the level of cubic action for perturbations.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Horndeski genesis: consistency of classical theory

Ageeva

Petrov

Рубаков

2020

Generating cosmological perturbations in non-singular Horndeski cosmologies

Ageeva

Petrov

Rubakov

2023

We construct a concrete model of Horndeski bounce with strong gravity in the past. Within this model we show that the correct spectra of cosmological perturbations may be generated at early contracting epoch, with mild fine-tuning ensuring that the scalar spectral tilt nS and tensor-to-scalar ratio r are consistent with observations. The smallness of r is governed by the smallness of the scalar sound speed. Arbitrarily small values of r are forbidden in our setup because of the strong coupling in the past. Nevertheless, we show that it is possible to generate perturbations in a controllable way, i.e. in the regime where the background evolution and perturbations are legitimately described within classical field theory and weakly coupled quantum theory.

Generating enhanced primordial GWs during inflation with intermittent violation of NEC and diminishment of GW propagating speed

Cai

Piao

2022

We investigate both the null energy condition (NEC) violating scenario and the cT-diminishing scenario for generating enhanced power spectrum of primordial gravitational waves (GWs) during inflation, where cT is the propagating speed of primordial GWs. Both of these two scenarios can be realized stably with theories beyond Horndeski, hence can be uniformly implemented within the framework of the effective field theory. We calculate the power spectrum of primordial GWs by assuming that the inflationary Universe undergoes three phases, where the violation of NEC or the diminishment of cT occurs in the intermediate phase. A template of the spectrum is given for the NEC-violating scenario. We also discuss the underlying relation and discrepancy between these two scenarios with a disformal transformation.