标题： 重力标量-张量理论的核合成限制 显示英文标题

标题： Nucleosynthesis Constraints on Scalar-Tensor Theories of Gravity

摘要： 我们研究了引力的无质量单场标量张量理论的宇宙演化，从 $e^+e^-$ 灭绝和核合成开始之前的时间，直到现在。 宇宙演化的进程以及最轻元素（主要是在早期宇宙中产生的那些）丰度的观测限制，对 $a(\phi)$ 的泰勒级数展开系数施加了约束，该系数规定了标量场与物质的耦合，并且是该理论中唯一的自由函数。 当 $a(\phi)$ 存在最小值时（即当理论演化趋向于广义相对论时），这些约束转化为对后牛顿参数 $\gamma$ 和 $\beta$ 的更强限制，比其他任何观测测试都要严格。 此外，我们的限制表明，即使在湮灭和核合成时期，如果不想过多或过少地产生 $^{4}$He，宇宙的演化也必须非常接近广义相对论所预测的那样。 因此，在如此早的时期，标量场对引力的贡献是非常小的。 显示英文摘要

摘要： We study the cosmological evolution of massless single-field scalar-tensor theories of gravitation from the time before the onset of $e^+e^-$ annihilation and nucleosynthesis up to the present. The cosmological evolution together with the observational bounds on the abundances of the lightest elements (those mostly produced in the early universe) place constraints on the coefficients of the Taylor series expansion of $a(\phi)$, which specifies the coupling of the scalar field to matter and is the only free function in the theory. In the case when $a(\phi)$ has a minimum (i.e., when the theory evolves towards general relativity) these constraints translate into a stronger limit on the Post-Newtonian parameters $\gamma$ and $\beta$ than any other observational test. Moreover, our bounds imply that, even at the epoch of annihilation and nucleosynthesis, the evolution of the universe must be very close to that predicted by general relativity if we do not want to over- or underproduce $^{4}$He. Thus the amount of scalar field contribution to gravity is very small even at such an early epoch.