$f(R,T)$引力中的大爆炸核合成与熵演化
Big Bang Nucleosynthesis and Entropy Evolution in $f(R,T)$ Gravity
摘要：
本文利用大爆炸核合成的约束条件，对$f(R,T)= R + χT$引力模型的模型参数$χ$进行了约束。我们解决了场方程和约束$χ$范围$-0.14 κ^{2} \leq χ\leq 0.84 κ^{2}$（其中$κ^{2} = \frac{8 πG}{c^{4}}$）从原始丰度的轻元素，如氦-4，氘和锂-7。我们发现氦-4和氘的丰度与理论预测一致，但是锂问题仍然存在于$f(R,T)$重力模型中。我们还研究了辐射宇宙和尘埃宇宙的$χ$约束参数空间的熵演化。我们报告，熵是常数时，$χ= 0$辐射占主导地位的宇宙，而尘埃宇宙，熵随时间增加。最后，我们使用的约束条件表明，$χ$的冷暗物质湮灭截面的影响可以忽略不计。
英文摘要：
The present article is devoted to constrain the model parameter $χ$ for the $f(R,T)= R + χT$ gravity model by employing the constraints coming from big bang nucleosynthesis. We solve the field equations and constrain $χ$ in the range $-0.14 κ^{2} \leq χ\leq 0.84 κ^{2}$ (where $κ^{2} = \frac{8 πG}{c^{4}}$) from the primordial abundances of light elements such as helium-4, deuterium and lithium-7. We found the abundances of helium-4 and deuterium agrees with theoretical predictions, however the lithium problem persists for the $f(R,T)$ gravity model. We also investigate the evolution of entropy for the constrained parameter space of $χ$ for the radiation and dust universe. We report that entropy is constant when $χ= 0$ for the radiation dominated universe, whereas for the dust universe, entropy increases with time. We finally use the constraints to show that $χ$ has negligible influence on the cold dark matter annihilation cross section.
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