Title: Galilean Genesis: an alternative to inflation Show Chinese title

Title: 伽利略生成：通货膨胀的替代方案

Abstract: We propose a novel cosmological scenario, in which standard inflation is replaced by an expanding phase with a drastic violation of the Null Energy Condition (NEC): \dot H >> H^2. The model is based on the recently introduced Galileon theories, that allow NEC violating solutions without instabilities. The unperturbed solution describes a Universe that is asymptotically Minkowski in the past, expands with increasing energy density until it exits the regime of validity of the effective field theory and reheats. This solution is a dynamical attractor and the Universe is driven to it, even if it is initially contracting. The study of perturbations of the Galileon field reveals some subtleties, related to the gross violation of the NEC and it shows that adiabatic perturbations are cosmologically irrelevant. The model, however, suggests a new way to produce a scale invariant spectrum of isocurvature perturbations, which can later be converted to adiabatic: the Galileon is forced by symmetry to couple to the other fields as a dilaton; the effective metric it yields on the NEC violating solution is that of de Sitter space, so that all light scalars will automatically acquire a nearly scale-invariant spectrum of perturbations. Show Chinese abstract

Abstract: 我们提出了一种新的宇宙学场景，在其中标准暴胀被一种急剧违反空能条件（NEC）的膨胀阶段所取代：\dot H >> H^2。该模型基于最近引入的Galileon理论，这些理论允许存在没有不稳定性的NEC违反解。未扰动解描述了一个过去渐近闵可夫斯基的宇宙，随着能量密度增加而膨胀，直到有效场论的适用范围失效并重新加热。这个解是一个动力学吸引子，即使宇宙最初处于收缩状态，也会被驱动到此解上。对Galileon场的扰动研究揭示了一些与NEC严重违反相关的微妙之处，并表明绝热扰动在宇宙学上无关紧要。然而，该模型提出了一种产生标度不变等曲率扰动谱的新方法，之后可以将其转换为绝热扰动：Galileon场由于对称性必须作为胀子与其他场耦合；在NEC违反解上它产生的有效度规是de Sitter空间的度规，因此所有轻标量都会自动获得几乎标度不变的扰动谱。