We study inflation, perturbations, non-gaussinity and late-time cosmological dynamics of a tachyon field both minimally and non-minimally coupled to gravity. By analyzing the parameters space of the model, the viability of the model in confrontation with recent observational data is considered. In a dynamical system technique, we study the phase space dynamics of both minimally and non-minimally coupled tachyon field. We find the fixed points (lines in our setup) and explore their stability. Also, we perform a statefinder diagnostic to both cases and show that the trajectories of the state finder pairs reach a stable state which is corresponding to a ΛCDM scenario.PACS numbers: 98.80. Cq , 95.36.+x

Motivated by α-attractor models, in this paper we consider a Gauss-Bonnet inflation with an E-model-type of potential. We consider the Gauss-Bonnet coupling function to be the same as the E-model potential. In the small α limit we obtain an attractor at r = 0 as expected, and in the large α limit we recover the Gauss-Bonnet model with potential and coupling function of the form φ 2n . We study perturbations and non-Gaussianity in this setup and we find some constraints on the model's parameters in comparison with PLANCK data sets. We study also the reheating epoch after inflation in this setup. For this purpose, we seek the number of e-folds and temperature during reheating epoch. These quantities depend on the model's parameter and the effective equation of state of the dominating energy density in the reheating era. We find some observational constraints on these parameters.PACS numbers: 04.50. Kd , 98.80.Cq , 98.80.Es

We study cosmological inflation on a warped DGP braneworld where inflaton field is nonminimally coupled to induced gravity on the brane. We present a detailed calculation of the perturbations and inflation parameters both in Jordan and Einstein frame. We analyze the parameters space of the model fully to justify about the viability of the model in confrontation with recent observational data. We compare the results obtained in these two frames also in order to judge which frame gives more acceptable results in comparison with observational data.PACS numbers: 98.80. Cq,

We consider two non-canonical scalar fields (tachyon and DBI) with E-model type of the potential. We study cosmological inflation in these models to find possible α-attractors. We show that similar to the canonical scalar field case, in both tachyon and DBI models there is a value of the scalar spectral index in small α limit which is just a function of the e-folds number. However, the value of ns in DBI model is somewhat different from the other ones. We also compare the results with Planck2015 TT, TE, EE+lowP data. The reheating phase after inflation is studied in these models which gives some more constraints on the model's parameters. PACS: 98.80.Cq , 98.80.Es

We study tachyon field inflation in the light of the Planck+WMAP+BICEP2+BAO joint data. While the minimally coupled tachyon field inflation is consistent with the Planck2013 data, it is not confirmed by the Planck+WMAP+BICEP2+BAO dataset. However, a nonminimally coupled tachyon field inflation is consistent with this joint dataset. PACS: 98.80. Bp, 98.80.Cq, 98.80.Es

We construct a holographic dark energy model in a braneworld setup that gravity is induced on the brane embedded in a bulk with Gauss-Bonnet curvature term. We include possible modification of the induced gravity and its coupling with a canonical scalar field on the brane. Through a perturbational approach to calculate the effective gravitation constant on the brane, we examine the outcome of this model as a candidate for holographic dark energy. PACS: 04.50.-h, 98.80.-k, 95.36.+x

We construct a DGP-inspired braneworld model where induced gravity on the brane is modified in the spirit of f (R) gravity and stringy effects are taken into account by incorporation of the Gauss-Bonnet term in the bulk action. We explore cosmological dynamics of this model and we show that this scenario is a successful alternative for dark energy proposal. Interestingly, it realizes the phantom-like behavior without introduction of any phantom field on the brane and the effective equation of state parameter crosses the cosmological constant line naturally in the same way as observational data suggest. PACS: 04.50.-h, 04.50. Kd, 95.36.+x

We study mimetic gravity in the presence of a DBI-like term which is a non-canonical setup of the scalar field's derivatives. We consider two general cases with varying and constant sound speeds and construct the potentials for both the DBI and Mimetic DBI models. By considering the power-law scale factor as a = a 0 t n , we seek for the observational viability of these models. We show that, the Mimetic DBI model in some ranges of the parameters space is free of ghost and gradient instabilities. By studying r − n s and α s − n s behavior in confrontation with Planck2018 data, we find some constraints on the model's parameters. We show that for the case with varying sound speed, although power-law DBI inflation is not consistent with Planck2018 TT, TE, EE+low E+lensing data, but the Mimetic DBI inflation is consistent with Planck2018 TT, TE, EE+low E+lensing data at 95% CL, in some ranges of the model's parameters space as 40 ≤ n ≤ 55 where the model is instabilities-free in these ranges of parameters too. For the constant sound speed, by adopting some sample values of c s , we study both DBI and Mimetic DBI model numerically and find n ∼ 10 2 for DBI model and n ∼ 10 for Mimetic DBI model. We also compare the results with Planck2018 TT, TE, EE+low E+lensing+BK14+BAO data and see that the DBI and Mimetic DBI model with varying sound speed are ruled out with these joint data. However, these models with constant sound speed are consistent with Planck2018 TT, TE, EE+low E+lensing+BK14+BAO data with n ∼ 10 2 for DBI model and n ∼ 10 for Mimetic DBI model. In this case, we find some tighter constraints on the corresponding sound speed. PACS: 98.80. Bp, 98.80.Cq, 98.80.Es