标题： 基于ACT的非最小红外引力重加热 显示英文标题

标题： Nonminimal infrared gravitational reheating in light of ACT

摘要： 暴胀被认为会产生大的红外标量涨落。此外，如果标量场$(\chi)$通过$\xi \chi^2 R$与引力非最小耦合，这些红外模在暴胀期间和暴胀后会经历\textit{超光速不稳定性}。那些大的非微扰红外模在后暴胀时期的地平线进入时可以集体产生热的大爆炸宇宙。我们确实发现，对于再加热的物态方程（EoS），$w_{\phi} > 1/3$，以及耦合强度，$\xi>1/6$，大的红外涨落会导致成功的再加热。我们进一步通过求解Jordan和爱因斯坦框架下的标准Boltzmann方程来分析微扰的再加热，并将结果与非微扰的结果进行比较。最后，我们将这个红外再加热场景嵌入到著名的$\alpha-$吸引子暴胀模型中，考察在最新的ACT、DESI结果下对模型参数可能的限制。 为了得到这些限制条件，我们考虑了张量-标量比的最新界限，即 $r_{0.05}\leq 0.038$，等倾角功率谱， $\mathcal{P}_{\mathcal{S}} \lesssim 8.3\times 10^{-11}$，以及相对论自由度的有效数， $\Delta N_{\rm eff} \lesssim 0.17 $。在这些限制条件下，我们发现只有状态方程 $w_{\phi}\gtrsim 0.6$能够成功实现再加热，这表明一类 $\alpha-$吸引子模型被青睐，并且将它们置于最新 ACT、DESI 数据的 $\sigma$ 区域内 $ n_s-r$平面中。 在此EoS范围内，我们发现耦合强度应位于 $2.11\lesssim\xi\lesssim 2.95$ 对于 $w_{\phi}=0.6$。 最后，我们计算了由标量红外模诱导的二次引力波信号，发现其强度足以被未来的引力波天文台（即BBO、DECIGO、LISA和ET）探测到。 显示英文摘要

摘要： Inflation is known to produce large infrared scalar fluctuations. Further, if a scalar field $(\chi)$ is non-minimally coupled with gravity through $\xi \chi^2 R$, those infrared modes experience \textit{tachyonic instability} during and after inflation. Those large non-perturbative infrared modes can collectively produce hot Big Bang universe upon their horizon entry during the post-inflationary period. We indeed find that for reheating equation of state (EoS), $w_{\phi} > 1/3$, and coupling strength, $\xi>1/6$, large infrared fluctuations lead to successful reheating. We further analyze perturbative reheating by solving the standard Boltzmann equation in both Jordan and Einstein frames, and compare the results with the non-perturbative ones. Finally, embedding this infrared reheating scenario into the well-known $\alpha-$attractor inflationary model, we examine possible constraints on the model parameters in light of the latest ACT, DESI results. To arrive at the constraints, we take into account the latest bounds on tensor-to-scalar ratio, $r_{0.05}\leq 0.038$, isocurvature power spectrum, $\mathcal{P}_{\mathcal{S}} \lesssim 8.3\times 10^{-11}$, and effective number of relativistic degrees of freedom, $\Delta N_{\rm eff} \lesssim 0.17 $. Subject to these constraints, we find successful reheating to occur only for EoS $w_{\phi}\gtrsim 0.6$, which translates to a sub-class of $\alpha-$attractor models being favored and placing them within the 2$\sigma$ region in the $ n_s-r$ plane of the latest ACT, DESI data. In this range of EoS, we find that the coupling strength should lie within $2.11\lesssim\xi\lesssim 2.95$ for $w_{\phi}=0.6$. Finally, we compute secondary gravitational wave signals induced by the scalar infrared modes, which are found to be strong enough to be detected by future GW observatories, namely BBO, DECIGO, LISA, and ET.