Phase Transitions During Inflation and the CMB Hemispherical Power Asymmetry

普朗克和WMAP已经观测到CMB功率的约10%的半球不对称性，这在具有统计各向同性高斯密度扰动的传统暴胀模型中无法解释。作为理解这一点的一种方法，该项目将研究在暴胀期间发生的相变的动力学，特别是经历转变的标量场的扰动谱。(Note这是第二个标量场，而不是暴胀子。）以前已经表明，这种过渡可以占标量场扰动与半球形的功率不对称的整个水平体积。该项目将在平台暴胀模型的背景下研究不对称性，特别是Starobinsky暴胀和非最小耦合暴胀模型，已知这些模型与谱指数和张量标量比的普朗克值自然相容。一旦标量场扰动的不对称性被理解，模型将被构建为将标量场扰动转化为具有半球功率不对称性的曲率扰动。这是具有挑战性的，因为该模型不应该产生相应的平均CMB温度的不对称性。该研究将用于测试基于标量场的模型是否可以产生半球CMB功率不对称，确定这样做所需的一般条件，如果不成功，确定无法构建此类模型的原因。

Planck and WMAP have observed a ~ 10% hemispherical asymmetry of the CMB power, which cannot be explained in the context of conventional inflation models with statistically isotropic Gaussian density perturbations. As an approach to understanding this, the project will investigate the dynamics of phase transitions which occur during inflation, in particular the spectrum of perturbations of a scalar field undergoing a transition. (Note that this is a second scalar field, not the inflaton.) It has previously been shown that such transitions can account for scalar field perturbations with a hemispherical power asymmetry across a horizon volume. The project will study the asymmetry in the context of plateau inflation models, in particular Starobinsky inflation and non-minimally coupled inflation models, which are known to be naturally compatible with the Planck values for the spectral index and tensor-to-scalar ratio. Once the asymmetry in the scalar field perturbation is understood, models will be constructed to translate the scalar field perturbation into a curvature perturbation with a hemispherical power asymmetry. This is challenging, as the model should not produce a corresponding asymmetry in the mean CMB temperature. The study will serve to test whether scalar field based models can generate a hemispherical CMB power asymmetry, identify the general conditions required to do so, and, if unsuccessful, determine the reasons why such models cannot be constructed.