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arXiv 1504.03544gr-qchep-th
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修正的Gauss-Bonnet引力中视视界上的广义热力学第二定律

Generalized second law of thermodynamics on the apparent horizon in modified Gauss-Bonnet gravity

A. Abdolmaleki, T. Najafi

摘要:

修正引力和广义热力学第二定律是现代宇宙学研究的热点。在这方面,我们研究的GSL的引力热力学的框架下修改的高斯-邦纳引力或f(G)-引力。我们考虑一个充满物质和辐射的空间FRW宇宙,它被具有Hawking温度的动态视视界所包围。对于两个可行的f(G)模型,我们首先数值求解控制f(G)-引力动力学的微分方程组。在此基础上,我们得到了哈勃参数、高斯-邦纳曲率不变项、密度和状态方程参数以及减速参数的演化。此外,我们检查了两个模型的能量条件,并最终检查了GSL的有效性。对于选定的f(G)模型,我们得出结论:两个模型都有稳定的de Sitter吸引子.状态方程参数在辐射/物质主导的时期表现得与LCDM模型非常相似,然后它们在到达w=-1的de Sitter吸引子之前进入幻影区域。减速参数从辐射/物质主导的时代开始,然后从宇宙减速过渡到加速,最后在后期接近德西特政权,正如预期的那样。此外,在标准辐射/物质主导时期,两种模型都遵守GSL。此后,当宇宙开始加速时,GSL在某些尺度因子范围内被破坏。在后期,GSL的演化预测了宇宙加速膨胀的绝热行为。

英文摘要:

Modified gravity and generalized second law (GSL) of thermodynamics are interesting topics in the modern cosmology. In this regard, we investigate the GSL of gravitational thermodynamics in the framework of modified Gauss-Bonnet gravity or f(G)-gravity. We consider a spatially FRW universe filled with the matter and radiation enclosed by the dynamical apparent horizon with the Hawking temperature. For two viable f(G) models, we first numerically solve the set of differential equations governing the dynamics of f(G)-gravity. Then, we obtain the evolutions of the Hubble parameter, the Gauss-Bonnet curvature invariant term, the density and equation of state parameters as well as the deceleration parameter. In addition, we check the energy conditions for both models and finally examine the validity of the GSL. For the selected f(G) models, we conclude that both models have a stable de Sitter attractor. The equation of state parameters behave quite similar to those of the LCDM model in the radiation/matter dominated epochs, then they enter the phantom region before reaching the de Sitter attractor with w=-1. The deceleration parameter starts from the radiation/matter dominated eras, then transits from a cosmic deceleration to acceleration and finally approaches a de Sitter regime at late times, as expected. Furthermore, the GSL is respected for both models during the standard radiation/matter dominated epochs. Thereafter when the universe becomes accelerating, the GSL is violated in some ranges of scale factor. At late times, the evolution of the GSL predicts an adiabatic behavior for the accelerated expansion of the universe.

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