Title: Equation of state during (p)reheating with trilinear interactions Show Chinese title

Title: 重加热期间具有三线性相互作用的状态方程

Abstract: We characterize the post-inflationary evolution of the equation of state of the universe from the end of inflation until the onset of radiation domination, when the inflaton is coupled to a daughter field through a trilinear interaction. We consider an inflaton potential that is quadratic near the minimum and flattens in the inflationary regime. By simulating the dynamics in 2+1-dimensional lattices, we have tracked the long-term evolution of the equation of state for about ten e-folds of expansion, for various coupling strengths. The trilinear interaction initially excites daughter field modes through a process of tachyonic resonance immediately after inflation and triggers a temporary deviation of the equation of state from $\bar{w} = 0$ to a maximum value $\bar{w} = \bar{w}_{\rm max} < 1/3$. However, at much later times, the inflaton homogeneous mode once again dominates the energy density, pushing the equation of state towards $\bar{w} = 0$ until the onset of perturbative reheating. By combining the lattice results with a Boltzmann approach, we characterize the entire post-inflationary expansion history, which allows to calculate precise predictions for the inflationary CMB observables. We also accurately compute the redshift of the stochastic gravitational wave background produced during preheating, and show that taking the temporary return of the equation of state towards $\bar{w} = 0$ into account can reduce the amplitude by many orders of magnitude relative to previous estimates. Show Chinese abstract

Abstract: 我们从暴胀结束到辐射主导开始，表征宇宙状态方程的暴胀后演化，此时暴胀子通过三线相互作用耦合到一个子场。 我们考虑一个在最小值附近为二次的暴胀势，并在暴胀阶段变平。 通过在2+1维晶格中模拟动力学，我们跟踪了约十个e-fold膨胀的状态方程的长期演化，针对不同的耦合强度。 三线相互作用在暴胀后立即通过一种瞬态共振过程激发子场模式，并导致状态方程从$\bar{w} = 0$暂时偏离到最大值$\bar{w} = \bar{w}_{\rm max} < 1/3$。 然而，在更晚的时间，暴胀子均匀模式再次主导能量密度，将状态方程推向$\bar{w} = 0$直到微扰再加热开始。 通过将晶格结果与玻尔兹曼方法相结合，我们表征了整个暴胀后膨胀历史，这使得可以计算暴胀CMB观测量的精确预测。 我们还准确计算了预加热期间产生的随机引力波背景的红移，并表明考虑到状态方程暂时回到$\bar{w} = 0$可以使振幅比之前估计减少多个数量级。