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arXiv 0904.2444hep-thastro-ph.HEgr-qc
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DGP膜宇宙学与夸克-强子相变

DGP brane cosmology and quark-hadron phase transition

K. Atazadeh, A. M. Ghezelbash, H. R. Sepangi

摘要:

在宇宙学的标准图景中,预测在大爆炸后大约10微秒发生了一个相变,伴随着电弱跃迁后的手征对称性破缺,将自由夸克和胶子的等离子体转化为强子。在一个有效的QCD模型中,我们考虑了DGP膜世界中的夸克-强子相变。我们研究的物理量的演变,有利于早期宇宙的研究,即能量密度,温度和标度因子之前,期间,和之后的相变。此外,由于早期宇宙的高能量密度,我们考虑了弗里德曼方程中出现的二次能量密度项。在DGP膜模型中,当哈勃半径远小于4D和5D区域的交叉长度时,这个项对应于弗里德曼方程的负分支(ε=-1)。我们发现,对于不同的膜上宇宙学常数λ,会发生相变,并导致夸克-胶子等离子体和强子流体的有效温度降低。然后我们考虑了在高低温下的光滑过渡区中的夸克-强子跃迁,并证明了在相变过程中,随着夸克-胶子等离子体有效温度的降低,这种跃迁也会发生.

英文摘要:

In the standard picture of cosmology it is predicted that a phase transition, associated with chiral symmetry breaking after the electroweak transition, has occurred at approximately 10 μseconds after the Big Bang to convert a plasma of free quarks and gluons into hadrons. We consider the quark-hadron phase transition in a DGP brane world scenario within an effective model of QCD. We study the evolution of the physical quantities useful for the study of the early universe, namely, the energy density, temperature and the scale factor before, during, and after the phase transition. Also, due to the high energy density in the early universe, we consider the quadratic energy density term that appears in the Friedmann equation. In DGP brane models such a term corresponds to the negative branch (ε=-1) of the Friedmann equation when the Hubble radius is much smaller than the crossover length in 4D and 5D regimes. We show that for different values of the cosmological constant on a brane, λ, phase transition occurs and results in decreasing the effective temperature of the quark-gluon plasma and of the hadronic fluid. We then consider the quark-hadron transition in the smooth crossover regime at high and low temperatures and show that such a transition occurs along with decreasing the effective temperature of the quark-gluon plasma during the process of the phase transition.

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