Testing a two field inflation beyond the slow-roll approximation

2018

Nuclear Physics B

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Focusing on the local type primordial non-Gaussianities, we study the bispectrum and trispectrum during a non-minimal slow-roll inflation. We use the so-called δN formalism to investigate the super-horizon evolution of the primordial perturbations in this setup. Firstly we obtain the main equations of the model and introduce the framework of the δN formalism for this case. Then we give analytical expressions for the nonlinear parameters describing the non-Gaussianity in the slowroll approximation. We analyze the bispectrum by its non-linear parameter, fNL. Furthermore, we calculate τNL and gNL which are non-linear parameters characterizing the amplitude of trispectrum. Finally, by adopting a quadratic form for both the potential and non-minimal coupling (NMC) function, we test our setup in the light of Planck2015 data and constrain the model parameters space. Although the non-Gaussianity parameters are so small in this setup, this model is consistent with recent observation. We extend our analysis to see the situation in the Einstein frame and compare the results in these two frames.PACS numbers: 98.80.Cq , 98.80.Es

Section: Introductionmentioning

confidence: 99%

The size of local bispectrum and trispectrum in a non-minimal inflation

Asadi

2018

Nuclear Physics B

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“…under the conditions 1 and |η| 1 show the inflation phase. In this extended setup, with GB correction, the slow-roll limits are asφ |3Hφ|,φ 2 V (φ), HĠ κ −2 and P ,X X κ −2 H 2 (see [34,77,98]).…”

Section: The General Gauss-bonnet Inflationmentioning

confidence: 99%

“…For more details about obtaining the equations presented in this section, see [12,76,77]. By having the required equations, in the next sections we explore the observational viability of some Gauss-Bonnet models.…”

Section: The General Gauss-bonnet Inflationmentioning

confidence: 99%

See 1 more Smart Citation

Gauss–Bonnet Inflation after Planck2018

Rashidi

2020

ApJ

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We study the primordial perturbations and reheating process in the models where the Gauss-Bonnet term is non-minimally coupled to the canonical and non-canonical (DBI and tachyon) scalar fields. We consider several potentials and Gauss-Bonnet coupling terms as power-law, dilaton-like, cosh-type, E-model and T-model. To seek the observational viability of these models, we study the scalar perturbations numerically and compare the results with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO joint data at 68% CL and 95% CL. We also study the tensor perturbations in confrontation with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO+ LIGO&Virgo2016 joint data at 68% CL and 95% CL. In this regard, we obtain some constraints on the Gauss-Bonnet coupling parameter β. Another important process in the early universe is the reheating phase after inflation which is necessary to reheat the universe for subsequent evolution. In this regard, we study the reheating process in these models and find some expressions for the e-folds number and temperature during that era. Considering that from Planck TT,TE,EE+lowEB+lensing data and BICEP2/Keck Array 2014, based on the ΛCDM+r + dns d ln k model, we have n s = 0.9658 ± 0.0038 and r < 0.072, we obtain some constraints on the e-folds number and temperature. From the values of the e-folds number and the effective equation of state and also the observationally viable value of the scalar spectral index, we explore the capability of the models in explaining the reheating phase. PACS: 98.80. Bp, 98.80.Cq, 98.80.Es

“…Also, in these models the perturbations are somewhat scale dependent and it is possible to have non-Gaussian distributed perturbations. We refer to [23,24,25,26] for some works on the issue of nonminimal derivatives in the early time accelerating expansion of the universe as well as the late time cosmic dynamics.…”

Section: Introductionmentioning

confidence: 99%

Observational Viability of an Inflation Model with E-model Nonminimal Derivative Coupling

Rashidi

2018

ApJ

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By starting with a two-fields model in which the fields and their derivatives are nonminimally coupled to gravity, and then by using a conformal gauge, we obtain a model in which the derivatives of the canonically normalized field are nonminimally coupled to gravity. By adopting some appropriate functions, we study two cases with constant and E-model nonminimal derivative coupling, while the potential in both cases is chosen to be E-model one. We show that in contrary to the single field α-attractor model that there is an attractor point in the large N and small α limits, in our setup and for both mentioned cases there is an attractor line in these limits that the r − ns trajectories tend to. By studying the linear and nonlinear perturbations in this setup and comparing the numerical results with Planck2015 observational data, we obtain some constraints on the free parameter α. We show that by considering the E-model potential and coupling function, the model is observationally viable for all values of M (mass scale of the model). We use the observational constraints on the tensor-to-scalar ratio and the consistency relation to obtain some constraints on the sound speed of the perturbations in this model. As a result, we show that in a nonminimal derivative α-attractor model, it is possible to have small sound speed and therefore large non-Gaussianity. PACS: 98.80.Cq , 98.80.Es