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Inspired by the entropy-area relation of black hole thermodynamics, we study the thermodynamics of cosmological apparent horizon in a spatially flat Friedmann-Robertson-Walker (FRW) universe in the framework of an Extended Uncertainty Principle (EUP). The adopted EUP naturally admits a minimal measurable momentum (equivalently a maximal measurable length), as an infrared cutoff in the theory. We derive the modified Friedmann equations in this setup and explore some predictions of these equations for the late time universe via distance measures. We show that in this framework it is possible to realize the late time cosmic speed-up and transition to the phantom phase of the equation of state parameter of the effective cosmic fluid without recourse to any dark energy component or modified gravity. Inspection of various distance measures in this framework shows that an EUP with a negative deformation parameter suffices for the interpretation of the late time asymptotically de Sitter universe with standard non-relativistic matter., Comment: 25 pages, 13 figures, Accepted for publication in The Astrophysical Journal

In this paper we construct a dissipative quintessential cosmic inflation. For this purpose, we add a multiplicative dissipative term in the standard quintessence field Lagrangian. We consider the specific form of dissipation as the time integral including the Hubble parameter and an arbitrary function that describes the dissipative properties of the quintessential scalar field. Inflation parameters and observables are calculated under slow-roll approximations and a detailed calculation of the cosmological perturbations is performed in this setup. We consider different forms of potentials and calculate the scalar spectral index and tensor-to-scalar ratio for a constant as well as variable dissipation function. To check the reliability of this model, a numerical analysis on the model parameters space is done in confrontation with recent observational data. By comparing the results with observational joint datasets at 68% and 95% confidence levels, we obtain some constraints on the model parameters space, specially the dissipation factor with e-folds numbers N = 55 and N = 60. As some specific results, we show that the power-law potential with a constant dissipation factor and N = 60 is mildly consistent with observational data in some restricted domains of the model parameter space with very small and negative dissipation factor and a negligible tensor-toscalar ratio. But this case with N = 55 is consistent with observation considerably. For power-law potential and variable dissipation factor as $Q = {\alpha}\phi^n$, the consistency with observation is also considerable with a reliable tensor-to-scalar ratio. The quadratic and quartic potentials with variable dissipation function as $Q = {\alpha}\phi^n$ are consistent with Planck2018 TT, TE, EE+lowE+lensing data at the 68% and 95% levels of confidence for some intervals of the parameter n., Comment: Accepted for publication in Physics of the Dark Universe, 37 pages, 14 figures, 8 tables

We study the intermediate tachyon inflation in an anisotropic background. By using the Friedmann equations obtained in the anisotropic geometry, we obtain the slow-roll parameters in the tachyon model. The presence of the anisotropic effects in the slow-roll parameters changes the perturbation parameters in our setup which may change its observational viability. To check this, we perform a numerical analysis and test the results with Planck2018 TT, TE, EE +lowE+lensing+BK14(18)+BAO data. We show that the intermediate anisotropic inflation in some ranges of the anisotropic and intermediate parameters is observationally viable. We also show that the equilateral amplitude of the non-gaussianity in our model is of the order of $10^{-2}-10^{-1}$. By studying the reheating process in our setup, we find that it is possible to have instantaneous reheating in this model. We also find that the temperature during the reheating in our setup is consistent with Big-Bang nucleosynthesis., Comment: 17 pages, 8 figures, 4 tables

We consider an intermediate Dirac-Born-Infeld (DBI) inflationary model in the presence of a minimal measurable length in the theory. We show that, the presence of a minimal measurable length modifies the definitions of the scalar and tensor spectral indices and also other inflation observables. This is due to modification of the momentum and corresponding wave number of the perturbations in the presence of a minimal length. By using the deformed definition of the scalar and tensor spectral indices, we perform numerical analysis on the intermediate DBI inflation model to find some constraints on the deformation parameter. In this regard, we compare our numerical results with both Planck2018 TT, TE, EE +lowE +lensing +BAO+ BK14 and Planck2018 TT, TE,EE +lowE+lensing+BK14 +BAO+LIGO $\&$ Virgo2016 data at the $68\%$ CL and $95\%$ CL. Our numerical study shows that the intermediate DBI inflation model in the presence of a minimal measurable length is observationally viable if the upper bound on the deformation parameter to be considered of the order of $10^{48}$ at $68\%$ CL and $10^{49}$ at $95\%$ CL. This is consistent with the results of other approaches to constrain such a quantity., Comment: 7 pages, 3 figures, 1 table

By adopting the intermediate and power-law scale factors, we study the tachyon inflation with constant sound speed. We perform some numerical analysis on the perturbation and non-gaussianity parameters in this model and compare the results with observational data. By using the constraints on the scalar spectral index and tensor-to-scalar-ratio, obtained from Planck2018 TT, TE, EE+lowE+lensing+BAO+BK14 data, the constraint on the running of the scalar spectral index obtained from Planck2018 TT, TE, EE+lowEB+lensing data, and constraint on tensor spectral index obtained from Planck2018 TT, TE, EE +lowE+lensing+BK14+BAO+LIGO and Virgo2016 data, we find the observationally viable ranges of the model's parameters at both $68\%$ CL and $95\%$ CL. We also analyze the non-gaussian features of the model in the equilateral and orthogonal configurations. Based on Planck2018 TTT, EEE, TTE and EET data, we find the constraints on the sound speed as $0.276\leq c_{s}\leq 1$ at $68\%$ CL, $0.213\leq c_{s}\leq 1$ at $95\%$ CL, and $0.186\leq c_{s}\leq 1$ at $97\%$ CL., Comment: 21 pages, 11 figures, 2 tables

Quantum gravitational effects usually are assumed to be important on small scale (Planck scale), but actually these effects are also very significant on large (cosmological) scales. It is recognized that in curved spacetime, the existence of a minimal measurable momentum is inevitable. In this paper, we study thermodynamic properties of the late time universe in the presence of a minimal measurable momentum cutoff that encodes infra-red modification of the underlying field theory. In this regard, we consider a non-relativistic regime and show that the existence of a minimal measurable momentum in the very essence of the theory leads to accelerating expansion of the universe, which can be interpreted as an alternative to Dark Energy. The universe in this model has experienced the phantom line crossing in the near past., Comment: 10 pages; 3 figures; Accepted for publication in Chinese Journal of Physics

We study the effects of the presence of the tachyon field around the black hole. We show that in presence of the tachyon field, unlike the ordinary canonical scalar field, the time evolution of the black hole mass depends on the potential of this field. By considering several types of potential, we study the behavior of the black hole mass and its time evolution and find some interesting results. We find that the presence of the tachyon field causes the accretion of the mass into the black hole. We also show that with linear and hilltop potentials, in some ranges of the parameters space, the mass of the black hole can decrease even without any Hawking radiation., Comment: 20 Pages, 12 Figures, Accepted for publication in International Journal of Modern Physics D

We study the intermediate inflation in the mimetic Dirac-Born-Infeld model. By considering the scale factor as $a=a_{0}\exp(bt^{\beta})$, we show that in some ranges of the intermediate parameters $b$ and $\beta$, the model is free of the ghost and gradient instabilities. We study the scalar spectral index, tensor spectral index, and the tensor-to-scalar ratio in this model and compare the results with Planck2018 TT, TE, EE+lowE+lensing +BAO +BK14 data at $68\%$ and $95\%$ CL. In this regard, we find some constraints on the intermediate parameters that lead to the observationally viable values of the perturbation parameters. We also seek the non-gaussian features of the primordial perturbations in the equilateral configuration. By performing the numerical analysis on the nonlinearity parameter in this configuration, we show that the amplitude of the non-gaussianity in the intermediate mimetic DBI model is predicted to be in the range $-16.7

We study cosmological dynamics of the energy-momentum squared gravity. By adding the squared of the matter field's energy-momentum tensor ($\zeta\, \textbf{T}^{2}$) to the Einstein Hilbert action, we obtain the Einstein's field equations and study the conservation law. We show that the presence of $\zeta\, \textbf{T}^{2}$ term, breaks the conservation of the energy-momentum tensor of the matter fields. However, an effective energy-momentum tensor in this model is conserved in time. By considering the FRW metric as the background, we find the Friedmann equations and by which we explore the cosmological inflation in $\zeta\,\textbf{T}^{2}$ model. We perform numerical analysis on the perturbation parameters and compare the results with Planck2018 different data sets at $68\%$ and $95\%$ CL, to obtain some constraints on the coupling parameter $\zeta$. We show that \textbf{ for $0< \zeta \leq 2.1\times 10^{-5}$, the $\zeta\, \textbf{T}^{2}$ gravity is an observationally viable model of inflation., Comment: 16 Pages, 9 Figures

We study the tachyon inflation in the presence of the superpotential as an inflationary potential. We study the primordial perturbations and their non-gaussian feature in the equilateral configuration. We use the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO joint data at $68\%$ CL and $95\%$ CL, to perform numerical analysis on the scalar perturbations and seek for the observational viability of the tachyon inflation with superpotential. We also check the observational viability of the model by studying the tensor part of the perturbations and comparing the results with Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO+ LIGO$\&$Virgo2016 joint data at $68\%$ CL and $95\%$ CL. By studying the phase space of the model's parameters, we predict the amplitude of the equilateral non-gaussianity in this model. The reheating phase after inflation is another issue that is explored in this paper. We show that, in some ranges of the model's parameters, it is possible to have an observationally viable tachyon model with superpotential., Comment: 25 pages, 8 figures, 5 tables

We consider the mimetic tachyon model in the Lagrange multiplier approach. We study both the linear and non-linear perturbations and find the perturbation and non-gaussianity parameters in this setup. By adopting two types of the scale factor as the power-law ($a=a_{0}\,t^{n}$) and intermediate ($a=a_{0}\exp(bt^{\beta})$) scale factors, we perform a numerical analysis on the model which is based on Planck2018 TT, TE, EE+lowE+lensing +BAO +BK14 and Planck2018 TTT, EEE, TTE and EET data sets. We show that the mimetic tachyon model with both the power-law and intermediate scale factors, in some ranges of its parameter space is instabilities-free and observationally viable. The power-law mimetic tachyon model with $26.3

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 $\beta$. 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 $\Lambda$CDM$+r+\frac{dn_{s}}{d\ln k}$ model, we have $n_{s}=0.9658\pm 0.0038$ 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., Comment: 52 pages, 16 figures, 16 tables

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 $\alpha_{s}-n_{s}$ 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 $40\leq n \leq 55$ 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 $n\sim 10^{2}$ for DBI model and $n\sim 10$ 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 $n\sim 10^{2}$ for DBI model and $n\sim 10$ for Mimetic DBI model. In this case, we find some tighter constraints on the corresponding sound speed., Comment: 45 pages, 17 figures, 13 tables

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 $\alpha$-attractor model that there is an attractor \textit{point} in the large $N$ and small $\alpha$ limits, in our setup and for both mentioned cases there is an attractor \emph{line} in these limits that the $r-n_{s}$ 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 $\alpha$. 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 $\alpha$-attractor model, it is possible to have small sound speed and therefore large non-Gaussianity., Comment: 18 pages, 8 figures, 4 tables, Accepted for publication in The Astrophysical Journal

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 $\alpha$-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 $\alpha$ limit which is just a function of the e-folds number. However, the value of $n_{s}$ 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., Comment: 22 pages, 9 figures, To appear in IJMPD

We study observational viability of Natural Inflation with a tachyon field as inflaton. By obtaining the main perturbation parameters in this model, we perform a numerical analysis on the parameter space of the model and in confrontation with $68\%$ and $95\%$ CL regions of Planck2015 data. By adopting a warped background geometry, we find some new constraints on the width of the potential in terms of its height and the warp factor. We show that the Tachyon Natural Inflation in the large width limit recovers the tachyon model with a $\phi^{2}$ potential which is consistent with Planck2015 observational data. Then we focus on the reheating era after inflation by treating the number of e-folds, temperature and the effective equation of state parameter in this era. Since it is likely that the value of the effective equation of state parameter during the reheating era to be in the range $0\leq \omega_{eff}\leq \frac{1}{3}$, we obtain some new constraints on the tensor to scalar ratio as well as the e-folds number and reheating temperature in this Tachyon Natural Inflation model., Comment: 19 pages, 6 figures, Accepted for publication in JCAP

Motivated by $\alpha$-attractor models, in this paper we consider a Gauss-Bonnet inflation with E-model type of potential. We consider the Gauss-Bonnet coupling function to be the same as the E-model potential. In the small $\alpha$ limit we obtain an attractor at $r=0$ as expected, and in the large $\alpha$ limit we recover the Gauss-Bonnet model with potential and coupling function of the form $\phi^{2n}$. We study perturbations and non-Gaussianity in this setup and we find some constraints on the model's parameters in comparison with PLANCK datasets. 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., Comment: 12 pages, 4 figures, Revised version, to appear in PRD

We study a nonminimal derivative inflationary model in the presence of the Gauss-Bonnet term. To have a complete treatment of the model, we consider a general form of the nonminimal derivative function and also the Gauss-Bonnet coupling term. By following the ADM formalism, expanding the action up to the third order in the perturbations and using the correlation functions, we study the perturbation and its non-Gaussian feature in details. We also study the consistency relation that gets modified in the presence of the Gauss-Bonnet term in the action. We compare the results of our consideration in confrontation with Planck2015 observational data and find some constraints on the model's parameters. Our treatment shows that this model in some ranges of the parameters is consistent with the observational data. Also, in some ranges of model's parameters, the model predicts blue-tilted power spectrum. Finally, we show that nonminimal derivative model in the presence of the GB term has capability to have large non-Gaussianity., Comment: 11 pages, 4 figures, accepted for publication in PRD

We study the dynamics of a generalized inflationary model in which both the scalar field and its derivatives are coupled to the gravity. We consider a general form of the nonminimal derivative coupling in order to have a complete treatment of the model. By expanding the action up to the second order in perturbation, we study the spectrum of the primordial modes of the perturbations. Also, by expanding the action up to the third order and considering the three point correlation functions, the amplitude of the non-Gaussianity of the primordial perturbations is studied both in equilateral and orthogonal configurations. Finally, by adopting some sort of potentials, we compare the model at hand with the Planck 2015 released observational data and obtain some constraints on the model's parameters space. As an important result, we show that the nonminimal couplings help to make models of chaotic inflation, that would otherwise be in tension with Planck data, in better agreement with the data. This model is consistent with observation at weak coupling limit., Comment: 22 pages, 8 figures

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., Comment: 9 pages, 4 figures, Accepted by PRD for Publication

We study the inflation in a model with a Gauss-Bonnet term which is non-minimally coupled to a DBI field. We study the spectrum of the primordial perturbations in detail. The non-Gaussianity of this model is considered and the amplitude of the non-Gaussianity is studied in both the equilateral and orthogonal configurations. By taking various functions of the DBI field, inflaton potential and the Gauss-Bonnet coupling term, we test the model with observational data and find some constraints on the Gauss-Bonnet coupling parameter., Comment: 31 pages, 6 figures, to appear in Phys. Rev. D

The recently released Planck data have constrained 4-dimensional inflationary parameters even more accurately than ever. We consider an extension of the braneworld model with induced gravity and a non-minimally coupled scalar field on the brane. We constraint the inflation parameters in this setup, by adopting six types of potential, in confrontation with the joint Planck+WMAP9+BAO data. We show that a potential of the type $V(\varphi)=V_{0}\exp(-\beta\varphi)$ has the best fit with newly released observational data., Comment: 14 pages, 6 figures

We consider cosmological dynamics of a canonical bulk scalar field, which is coupled non-minimally to 5-dimensional Ricci scalar in a DGP setup. We show that presence of this non-minimally coupled bulk scalar field affects the jump conditions of the original DGP model significantly. Within a superpotential approach, we perform some numerical analysis of the model parameter space and consider bulk-brane energy exchange in this setup. Also we show that the normal, ghost-free branch of the DGP solutions in this case has the potential to realize a self-consistent phantom-like behavior and therefore explains late time acceleration of the universe in a consistent way., Comment: 25 pages, Accepted for publication in Astrophyics and Space Science

We analyze the background cosmology for an extension of the DGP gravity with Gauss-Bonnet term in the bulk and $f(R)$ gravity on the brane. We investigate implications of this setup on the late-time cosmic history. Within a dynamical system approach, we study cosmological dynamics of this setup focusing on the role played by curvature effects. Finally we constraint the parameters of the model by confrontation with recent observational data., Comment: 22 pages, Accepted for publication in Adv. High Energy Phys

We study cosmological inflation on a warped DGP braneworld where inflaton field is non-minimally 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., Comment: 40 pages, 23 figures, Revised version, Accepted for publication in Phys. Rev. D

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., Comment: 13 pages, accepted for publication in IJMPD

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., Comment: 16 pages, 6 figures, Accepted for publication in JCAP

We construct a holographic dark energy model with a non-minimally coupled scalar field on the brane where Gauss-Bonnet and Induced Gravity effects are taken into account. This model provides a wide parameter space with several interesting cosmological implications. Especially, the equation of state parameter of the model crosses the phantom divide line and it is possible to realize bouncing solutions in this setup., Comment: 20 pages, 3 eps figures, to appear in IJTP