排序方式： 共有19条查询结果，搜索用时 15 毫秒
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Adnan Aslam Mubasher Jamil Davood Momeni Ratbay Myrzakulov Muneer Ahmad Rashid Muhammad Raza 《Astrophysics and Space Science》2013,348(2):533-540
In literature usual point like symmetries of the Lagrangian have been introduced to study the symmetries and the structure of the fields. This kind of Noether symmetry is a subclass of a more general family of symmetries, called Noether gauge symmetries (NGS). Motivated by this mathematical tool, in this paper, we study the generalized Noether symmetry of quintom model of dark energy, which is a two component fluid model with quintessence and phantom scalar fields. Our model is a generalization of the Noether symmetries of a single and multiple components which have been investigated in detail before. We found the general form of the quintom potential in which the whole dynamical system has a point like symmetry. We investigated different possible solutions of the system for diverse family of gauge function. Specially, we discovered two family of potentials, one corresponds to a free quintessence (phantom) and the second is in the form of quadratic interaction between two components. These two families of potential functions are proposed from the symmetry point of view, but in the quintom models they are used as phenomenological models without clear mathematical justification. From integrability point of view, we found two forms of the scale factor: one is power law and second is de-Sitter. Some cosmological implications of the solutions have been investigated. 相似文献
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Kazuharu Bamba Mubasher Jamil D. Momeni Ratbay Myrzakulov 《Astrophysics and Space Science》2013,344(1):259-267
We study the generalized second law (GSL) of thermodynamics in f(T) cosmology, where T is the torsion scalar in teleparallelism. We consider the universe as a closed bounded system filled with n component fluids in the thermal equilibrium with the cosmological boundary. We use two different cosmic horizons: the future event horizon and the apparent horizon. We show the conditions under which the GSL will be valid in specific scenarios of the quintessence and the phantom energy dominated eras. Further we associate two different entropies with the cosmological horizons: with a logarithmic correction term and a power-law correction term. We also find the conditions for the GSL to be satisfied or violated by imposing constraints on model parameters. 相似文献
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We investigate the bounce cosmology induced by inhomogeneous viscous fluids in FRW space-time (non necessarily flat), taking into account the early-time acceleration after the bounce. Different forms for the scale factor and several examples of fluids will be considered. We also analyze the relation between bounce and finite-time singularities and between the corresponding fluids realizing this scenarios. In the last part of the work, the study is extended to the framework of f(R)-modified gravity, where the modification of gravity may also be considered as an effective (viscous) fluid producing the bounce. 相似文献
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D. Dwivedee B. Nayak M. Jamil L. P. Singh R. Myrzakulov 《Journal of Astrophysics and Astronomy》2014,35(1):97-106
In this work, we study the evolution of primordial black holes within the context of loop quantum cosmology. First we calculate the scale factor and energy density of the Universe for different cosmic era and then taking these as inputs, we study evolution of primordial black holes. From our estimation it is found that accretion of radiation does not affect evolution of primordial black holes in loop quantum cosmology. We also conclude that due to slow variation of scale factor, the upper bound on initial mass fraction of presently evaporating PBHs are much greater in loop quantum cosmology than the standard case. 相似文献
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Mubasher Jamil Yerlan Myrzakulov Olga Razina Ratbay Myrzakulov 《Astrophysics and Space Science》2011,336(2):315-325
The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy and dark matter. In this paper,
we have modeled MCG in the framework of f-essence cosmology. By constructing an equation connecting the MCG and the f-essence,
we solve it to obtain explicitly the pressure and energy density of MCG. As special cases, we obtain both positive and negative
pressure solutions for suitable choices of free parameters. We also calculate the state parameter which describes the phantom
crossing. 相似文献
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Surajit Chattopadhyay Abdul Jawad Davood Momeni Ratbay Myrzakulov 《Astrophysics and Space Science》2014,353(1):279-292
We work on the reconstruction scenario of pilgrim dark energy (PDE) in f(T,T G ). In PDE model it is assumed that a repulsive force that is accelerating the Universe is phantom type with (w DE f(T,T G ) models and correspondingly evaluate equation of state parameter for various choices of scale factor. Also, we assume polynomial form of f(T,T G ) in terms of cosmic time and reconstruct H and w DE in this manner. Through discussion, it is concluded that PDE shows aggressive phantom-like behavior for s=?2 in f(T,T G ) gravity. 相似文献