Amin Salehi
University of Gilan
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Publication
Featured researches published by Amin Salehi.
Journal of Cosmology and Astroparticle Physics | 2011
Hossein Farajollahi; Amin Salehi; F. Tayebi; Arvin Ravanpak
We study general properties of attractors for tachyonic potential chameleon scalar-field model which possess cosmological scaling solutions. An analytic formulation is given to obtain fixed points with a discussion on their stability. The model predicts a dynamical equation of state parameter with phantom crossing behavior for an accelerating universe. We constrain the parameters of the model by best fitting with the recent data-sets from supernovae and simulated data points for redshift drift experiment generated by Monte Carlo simulations.
Journal of Cosmology and Astroparticle Physics | 2010
Hossein Farajollahi; Amin Salehi
We investigate chameleonic Brans-Dicke model applied to the FRW universes. A framework to study stability and attractor solutions in the phase space is developed for the model. We show that depending on the matter field and stability conditions, it is possible to realize phantom-like behavior without introducing phantom filed in the model while the stability is fulfilled and phantom crossing occurs. The statefinder parameters to the model for different kinds of matter interacting with the chameleon scalar field are studied. We also compare our model with present day observations.
International Journal of Modern Physics | 2010
Hossein Farajollahi; Amin Salehi
We study in this paper chameleon cosmology applied to Friedmann–Robertson–Walker space, which gives rise to the equation of state (EoS) parameter larger than -1 in the past and less than -1 today, satisfying current observations. We also study cosmological constraints on the model using the time evolution of the cosmological redshift of distant sources, which directly probes the expansion history of the universe. Due to the evolution of the universes expansion rate, the model-independent cosmological redshift drift (CRD) test is expected to experience a small, systematic drift as a function of time. The model is supported by the observational data obtained from the test.
Physical Review D | 2011
Hossein Farajollahi; Amin Salehi
We study the general properties of attractors in a cosmological model with tachyonic potential and a scalar field non-minimally coupled to matter. A general analytic formulation is given to derive fixed points with a discussion on their stability. We also check the consistency of the model by fitting it to the supernovae type Ia data.
Astrophysics and Space Science | 2012
Hossein Farajollahi; Mehrdad Farhoudi; Amin Salehi; Hossein Shojaie
In this paper we consider Chameleonic Generalized Brans–Dicke Cosmology in the framework of FRW universes. The bouncing solution and phantom crossing is investigated for the model. Two independent cosmological tests: Cosmological Redshift Drift (CRD) and distance modulus are applied to test the model with the observation. PACS numbers: 04.20.Cv; 04.50.-h; 04.60.Ds; 98.80.Qc
Journal of Cosmology and Astroparticle Physics | 2011
Hossein Farajollahi; Amin Salehi
We investigate the dynamics of the chameleonic Generalised Brans-Dicke model in flat FRW cosmology. In a new approach, a framework to study stability and attractor solutions in the phase space for the model is developed by simultaneously best fitting the stability and model parameters with the observational data. The results show that for an accelerating universe the phantom crossing does not occur in the past and near future.
Canadian Journal of Physics | 2011
Hossein Farajollahi; Amin Salehi; F. Tayebi
In this paper, we investigate the validity of the generalized second law of thermodynamics in flat Friedmann–Lemaitre–Robertson–Walker chameleon cosmology where the boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. It has been shown that, in a bouncing scenario for the universe with phantom crossing, the total entropy decreases with time in the contracting epoch, whereas, the dynamics of the internal and horizon entropies depend on the behaviour of both the equation of state and the Hubble parameters.
Astrophysics and Space Science | 2011
Hossein Farajollahi; Amin Salehi; F. Tayebi
In this paper, the generalized second law (GSL) of thermodynamics and entropy is revisited in the context of cosmological models with bouncing behavior such as chameleon cosmology where the boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. From a thermodynamic point of view, to link between thermodynamic and geometric parameters in cosmological models, we introduce “entropy rate of change multiplied by the temperature” as a model independent thermodynamic state parameter together with the well known {r,s} statefinder to differentiate the dark energy models.
Journal of Cosmology and Astroparticle Physics | 2011
H. Farajollahi; Amin Salehi; Asieh Shahabi
We study the dynamics of the scalar tensor cosmological model in the presence of tachyon field. In an alternative approach, in two exponential and power law form of the scalar field functions in the model, field equations are solved by simultaneously best fitting the model parameters with the most recent observational data. This approach gives us an observationally verified interpretation of the dynamics of the universe. We then discuss the best fitted of equation of state parameter, the statefinder parameters and the reconstructed scalar field in the model.
Astrophysics and Space Science | 2012
H. Farajollahi; Amin Salehi
In this article we study the properties of the flat FRW chameleon cosmology in which the cosmic expansion of the Universe is affected by the chameleon field and dark energy. In particular, we perform a detailed examination of the model in the light of numerical analysis. The results illustrate that the interacting chameleon filed plays an important role in late time universe acceleration and phantom crossing.