标题： 光锥上的规范不变性：曲率扰动和辐射自由度 显示英文标题

标题： Gauge invariance on the light-cone: curvature perturbations and radiative degrees of freedom

摘要： 我们推导了观测光锥上一些相关的宇宙学规范不变变量的表达式，例如Mukhanov-Sasaki变量以及$E$和$B$张量扰动模式。 由于光锥的结构并不直接反映FLRW对称性，我们发展了一种与坐标无关的形式，并根据其螺旋态对扰动进行分类。 尽管我们研究的是线性扰动，但我们的形式可以很容易地扩展到非线性理论，并为研究宇宙扰动在从早期到晚期宇宙沿观测光锥的演化奠定基础。 显示英文摘要

摘要： We derive the expressions on the observed light-cone for some relevant cosmological gauge invariant variables, such as the Mukhanov-Sasaki variable and $E$- and $B$- modes of the tensor perturbations. Since the structure of the light-cone does not reflect in a direct way the FLRW symmetries, we develop a formalism which is coordinate independent and classifies the perturbations according to their helicities. Even though we work with linear perturbations, our formalism can be readily extended to non-linear theory and put the basis to study the evolution of cosmological perturbations, since the early- until the the late- time Universe, directly along the observed light-cone.