标题： 暴胀后阶段比辐射更坚硬和Palatini形式 显示英文标题

标题： Post-inflationary phases stiffer than radiation and Palatini formulation

摘要： 如果暴胀场和第五元素场被识别，背景几何通过刚性时期演化，其膨胀率低于辐射主导等离子体的膨胀率。 对于某些暴胀势能类型，这种情形与当前的观测证据相矛盾，因为相应的张量与标量比过大。 当引力作用被补充一个爱因斯坦-希尔伯特项的二次贡献时，对第五元素暴胀进行分析。 在Palatini形式中，添加这样的项在暴胀阶段以及随后的刚性时期不会影响标量模式，但它会抑制张量功率谱和张量与标量比。 虽然在Palatini形式中导致第五元素暴胀动力学的幂律势能再次可行，但遗迹引力波谱的高频尖峰被压缩，并且当作用中出现的高阶贡献被明确地与暴胀场解耦时，整个信号都会被抑制。 显示英文摘要

摘要： If the inflaton and the quintessence fields are identified, the background geometry evolves through a stiff epoch undershooting the expansion rate of a radiation-dominated plasma. For some classes of inflationary potentials this scenario is at odds with the current observational evidence since the corresponding tensor-to-scalar ratio is too large. Quintessential inflation is analyzed when the gravitational action is supplemented by a contribution quadratic in the Einstein-Hilbert term. In the Palatini formulation the addition such a term does not affect the scalar modes during the inflationary phase and throughout the course of the subsequent stiff epoch but it suppresses the tensor power spectrum and the tensor-to-scalar ratio. While in the Palatini formulation the power-law potentials leading to a quintessential inflationary dynamics are again viable, the high-frequency spike of the relic graviton spectrum is squeezed and the whole signal is suppressed at least when the higher-order contributions appearing in the action are explicitly decoupled from the inflaton.