The quantum properties of O（2,2） string cosmology with a dilaton potential are studied in this paper. The cosmological solutions are obtained on three-dlmensional space-time. Moreover, the quantum probability of tra...The quantum properties of O（2,2） string cosmology with a dilaton potential are studied in this paper. The cosmological solutions are obtained on three-dlmensional space-time. Moreover, the quantum probability of transition between two duality universe is calculated through a Wheeler-De Witt approach.展开更多
A model of a cloud formed by massive strings is used as a source of Bianchi type II cases. We assume that the expansion （θ） in the model is proportional to the shear （σ）. To get an exact solution, we consider th...A model of a cloud formed by massive strings is used as a source of Bianchi type II cases. We assume that the expansion （θ） in the model is proportional to the shear （σ）. To get an exact solution, we consider the equation of state of the fluid to be in the stiff form. It is found that the bulk viscosity played a very important role in the history of the universe. In the presence of bulk viscosity the particles dominate over strings whereas in the absence of it, strings dominate over the particles, which is not consistent with recent observations. Also we observe that the viscosity causes the expansion of the universe to be accelerating. Our models are evolving from an early decelerating phase to a late time accelerating phase. The physical and geometrical behaviors of these models are discussed.展开更多
In recent works, a construction was proposed resulting in emergent universes inside black holes. This result can be obtained from a 4D black hole embedded in a 5D spacetime with the fifth dimension compactified on a c...In recent works, a construction was proposed resulting in emergent universes inside black holes. This result can be obtained from a 4D black hole embedded in a 5D spacetime with the fifth dimension compactified on a circle [0, 2] (0 and 2 are identified) such that the two branes are at 0 and 1. In the present work, we study this setup by deriving particles’ equations of motion in the new universes, based on redefining energy and angular momentum. This leads to disappearance of the singularity in centers of black holes in classical General Relativity.展开更多
In this letter, we report on our trials to remove the instability of black holes in brane world cosmological models consisting of two branes and a bulk. In order to resolve this problem, general types of interaction p...In this letter, we report on our trials to remove the instability of black holes in brane world cosmological models consisting of two branes and a bulk. In order to resolve this problem, general types of interaction potentials were employed. Careful analyses have shown that although the black holes instabilities were removed, a sort of arbitrariness adherent to the motion of the two branes towards each other has taken place leading to an unstable system. Thus, the models seem to us rather paradoxical.展开更多
The locally rotationally symmetric Bianchi-type II string cosmological models with bulk viscosity are obtained, where an equation of state, , and a relation between metric potentials, , are adopted. The physical featu...The locally rotationally symmetric Bianchi-type II string cosmological models with bulk viscosity are obtained, where an equation of state, , and a relation between metric potentials, , are adopted. The physical features of the models are also discussed. In special cases the model reduces to the string models without viscosity that was previously given in the literatures.展开更多
Utilizing the quantum statistical method and applying the new state density equation motivated by generalized uncertainty principle in quantum gravitaty, we avoid the difficulty in solving wave equation and directly c...Utilizing the quantum statistical method and applying the new state density equation motivated by generalized uncertainty principle in quantum gravitaty, we avoid the difficulty in solving wave equation and directly calculate the partition function of bosonic and fermionic field on the background of rotating and charged black string. Then near the cosmological horizon, entropies of bosonic and fermionic field are calculated on the background of black string. When constant A introduced in generalized uncertainty principle takes a proper value, we derive Bekenstein- Hawking entropy and the correction value corresponding cosmologicaJ horizon on the background of rotating and charged black string. Because we use the new state density equation, in our calculation there are not divergent term and small mass approximation in the original brick-wall method. From the view of quantum statistic mechanics, the correction value to Bekenstein-Hawking entropy of the black string is derived. It makes people deeply understand the correction value to the entropy of the black string cosmological horizon in non-spherical coordinate spacetime.展开更多
We present a class of new exact solutions in string cosmology theory, and the solutions describe a homogeneous but anisotropie plane-symmetric string universe within the framework of Bianehi type-I cosmology. Some sol...We present a class of new exact solutions in string cosmology theory, and the solutions describe a homogeneous but anisotropie plane-symmetric string universe within the framework of Bianehi type-I cosmology. Some solutions previously discussed are included in the class of exact solutions as the special cases. Our result may provide further quantitative description and theoretical basis for the string cosmology model.展开更多
Five-dimensional space-time string cosmological models generated by a cloud of strings with particles attached to them are studied in the Brans-Dicke theory. We obtain two types of interesting models by taking up the ...Five-dimensional space-time string cosmological models generated by a cloud of strings with particles attached to them are studied in the Brans-Dicke theory. We obtain two types of interesting models by taking up the cases of geometric strings （or Nambu strings） and p-strings （Takabayasi strings）, and study their different physi- cal and dynamical properties. The roles of the scalar field in getting different phases, such as the inflationary phase and the string-dominated phase, are discussed. An in- teresting feature obtained here is that in one of the models there is a ＂bounce＂ at a particular instant of its evolution.展开更多
In this paper,we present two non-perturbative string cosmological solutions without curvature singularities for the bosonic gravi-dilaton system.These solutions are general in that they can straightforwardly match the...In this paper,we present two non-perturbative string cosmological solutions without curvature singularities for the bosonic gravi-dilaton system.These solutions are general in that they can straightforwardly match the perturbative solution to arbitrarily high orders in the perturbative region.The first solution includes non-perturbative α’corrections based on Hohm-Zwiebach action.We then use the simple phenomenological map between the α’ and loop corrected theories in string cosmology to construct a non-perturbative loop corrected non-singular solution.Both solutions are non-singular everywhere.Therefore,the pre-and post-big-bangs are smoothly connected by these solutions.展开更多
基金The project supported by the Natural Science Foundation of Sichuan Normal University
文摘The quantum properties of O（2,2） string cosmology with a dilaton potential are studied in this paper. The cosmological solutions are obtained on three-dlmensional space-time. Moreover, the quantum probability of transition between two duality universe is calculated through a Wheeler-De Witt approach.
基金supported by a research fund from the Mahshahr Branch of Islamic Azad University under the project entitled "Study of the homogenous and anisotropic cosmological models by considering the gravitational effects of viscosity and cosmic strings"
文摘A model of a cloud formed by massive strings is used as a source of Bianchi type II cases. We assume that the expansion （θ） in the model is proportional to the shear （σ）. To get an exact solution, we consider the equation of state of the fluid to be in the stiff form. It is found that the bulk viscosity played a very important role in the history of the universe. In the presence of bulk viscosity the particles dominate over strings whereas in the absence of it, strings dominate over the particles, which is not consistent with recent observations. Also we observe that the viscosity causes the expansion of the universe to be accelerating. Our models are evolving from an early decelerating phase to a late time accelerating phase. The physical and geometrical behaviors of these models are discussed.
文摘In recent works, a construction was proposed resulting in emergent universes inside black holes. This result can be obtained from a 4D black hole embedded in a 5D spacetime with the fifth dimension compactified on a circle [0, 2] (0 and 2 are identified) such that the two branes are at 0 and 1. In the present work, we study this setup by deriving particles’ equations of motion in the new universes, based on redefining energy and angular momentum. This leads to disappearance of the singularity in centers of black holes in classical General Relativity.
文摘In this letter, we report on our trials to remove the instability of black holes in brane world cosmological models consisting of two branes and a bulk. In order to resolve this problem, general types of interaction potentials were employed. Careful analyses have shown that although the black holes instabilities were removed, a sort of arbitrariness adherent to the motion of the two branes towards each other has taken place leading to an unstable system. Thus, the models seem to us rather paradoxical.
文摘The locally rotationally symmetric Bianchi-type II string cosmological models with bulk viscosity are obtained, where an equation of state, , and a relation between metric potentials, , are adopted. The physical features of the models are also discussed. In special cases the model reduces to the string models without viscosity that was previously given in the literatures.
基金Supported by the Shanxi Natural Science Foundation of China under Grant No.2006011012the Doctoral Scientific Research Starting Foundation of Shanxi Datong University
文摘Utilizing the quantum statistical method and applying the new state density equation motivated by generalized uncertainty principle in quantum gravitaty, we avoid the difficulty in solving wave equation and directly calculate the partition function of bosonic and fermionic field on the background of rotating and charged black string. Then near the cosmological horizon, entropies of bosonic and fermionic field are calculated on the background of black string. When constant A introduced in generalized uncertainty principle takes a proper value, we derive Bekenstein- Hawking entropy and the correction value corresponding cosmologicaJ horizon on the background of rotating and charged black string. Because we use the new state density equation, in our calculation there are not divergent term and small mass approximation in the original brick-wall method. From the view of quantum statistic mechanics, the correction value to Bekenstein-Hawking entropy of the black string is derived. It makes people deeply understand the correction value to the entropy of the black string cosmological horizon in non-spherical coordinate spacetime.
基金Supported by the National Natural Science Foundation of China under Grant No 10575140 the National Basic Research Programme of China under Grant No 2003CB716300, the Foundation of China Academy of Engineering Physics, and the National Science Foundation of Chongqing under Grant No 8562.
文摘We present a class of new exact solutions in string cosmology theory, and the solutions describe a homogeneous but anisotropie plane-symmetric string universe within the framework of Bianehi type-I cosmology. Some solutions previously discussed are included in the class of exact solutions as the special cases. Our result may provide further quantitative description and theoretical basis for the string cosmology model.
文摘Five-dimensional space-time string cosmological models generated by a cloud of strings with particles attached to them are studied in the Brans-Dicke theory. We obtain two types of interesting models by taking up the cases of geometric strings （or Nambu strings） and p-strings （Takabayasi strings）, and study their different physi- cal and dynamical properties. The roles of the scalar field in getting different phases, such as the inflationary phase and the string-dominated phase, are discussed. An in- teresting feature obtained here is that in one of the models there is a ＂bounce＂ at a particular instant of its evolution.
基金supported by the Sichuan Science and Technology Program(2022YFG0317)supported by the Tianfu talent plan and FXHU.
文摘In this paper,we present two non-perturbative string cosmological solutions without curvature singularities for the bosonic gravi-dilaton system.These solutions are general in that they can straightforwardly match the perturbative solution to arbitrarily high orders in the perturbative region.The first solution includes non-perturbative α’corrections based on Hohm-Zwiebach action.We then use the simple phenomenological map between the α’ and loop corrected theories in string cosmology to construct a non-perturbative loop corrected non-singular solution.Both solutions are non-singular everywhere.Therefore,the pre-and post-big-bangs are smoothly connected by these solutions.
