大爆炸核合成对$f(T,T_G)$引力的约束
Big Bang Nucleosynthesis constraints on $f(T,T_G)$ gravity
摘要：
我们面对的是$f(T,T_G)$引力，以及大爆炸核合成（BBN）的要求。前者是使用扭转标量，以及远程平行等效的高斯-邦纳项，在拉格朗日，导致修改后的弗里德曼方程，其中额外的扭转项构成一个有效的暗能量部门。我们计算了冻结温度$T_f$的偏差，与$Λ$ CDM范式相比，由额外的扭转项引起的。然后，我们施加五个特定的$f(T,T_G)$模型，我们提取的约束条件的模型参数，以便比率$|ΔT_f/ T_f|$，以满足观测的BBN界。正如我们所发现的，在大多数模型中，所涉及的参数如预期的那样被限制在它们的广义相对论值周围的窄窗口中，如在幂律模型中，指数$n$需要为$n\lesssim 0.5$。然而，对数模型可以很容易地满足BBN约束的模型参数的大区域。在今后的建模中应考虑这一特点。
英文摘要：
We confront $f(T,T_G)$ gravity, with Big Bang Nucleosynthesis (BBN) requirements. The former is obtained using both the torsion scalar, as well as the teleparallel equivalent of the Gauss-Bonnet term, in the Lagrangian, resulting to modified Friedmann equations in which the extra torsional terms constitute an effective dark energy sector. We calculate the deviations of the freeze-out temperature $T_f$, caused by the extra torsion terms in comparison to $Λ$CDM paradigm. Then we impose five specific $f(T,T_G)$ models and we extract the constraints on the model parameters in order for the ratio $|ΔT_f/ T_f|$ to satisfy the observational BBN bound. As we find, in most of the models the involved parameters are bounded in a narrow window around their General Relativity values as expected, as in the power-law model where the exponent $n$ needs to be $n\lesssim 0.5$. Nevertheless the logarithmic model can easily satisfy the BBN constraints for large regions of the model parameters. This feature should be taken into account in future model building.
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