Positivity bounds from multiple vacua and their cosmological consequences
Positivity bounds from multiple vacua and their cosmological consequences
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DOI：
10.1088/1475-7516/2022/06/031
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发表时间：
2022-02
影响因子：
6.4
通讯作者：
S. Melville;J. Noller
中科院分区：
文献类型：
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作者：
S. Melville;J. Noller
正界——由紫外线的幺正性、因果性和局域性基本公理对任何低能有效场论施加的约束——最近被用来约束与宇宙学相关的各种有效场论。然而，迄今为止，大多数这些界限都假设存在一个洛伦兹不变真空，其中所有场的期望值都为零，而在许多宇宙学相关模型中，情况并非如此。我们通过研究一个简单的示例模型（协变伽利略模型）来探索克服这一限制的方法，该模型拥有洛伦兹不变真空的单参数族以及多个升压破坏真空。这些真空中的每一个都有一组相应的正边界，我们展示了如何使用特定的（超出前向极限）边界来绘制参数空间，根据该真空可以在UV理论中持续存在，发现通常存在一些区域，其中没有一个、一个或多个有效场论真空可以与UV中的幺正性、因果性和局域性相一致。最后，我们讨论这张图和宇宙学观测之间的相互作用。我们发现，观测上有利的参数空间区域与一大类真空不相容，相反，特定的突破真空将意味着排除其他观测上有利的宇宙论的正边界。我们还确定了一个与宇宙学背景“最接近”的特定助推突破真空，并表明我们考虑的特定正性界限将伽利略参数空间的宇宙学有利区域减少了高达 70％，从而排除了在此过程中立方伽利略具有正系数的绝大多数宇宙学。
Positivity bounds — constraints on any low-energy effective field theory imposed by the fundamental axioms of unitarity, causality and locality in the UV — have recently been used to constrain various effective field theories relevant for cosmology. However, to date most of these bounds have assumed that there is a single Lorentz-invariant vacuum in which all fields have zero expectation value and in many cosmologically relevant models this is not the case. We explore ways to overcome this limitation by investigating a simple example model, the covariant Galileon, which possesses a one-parameter family of Lorentz-invariant vacua as well as multiple boost-breaking vacua. Each of these vacua has a corresponding set of positivity bounds, and we show how a particular (beyond-the-forward-limit) bound can be used to map out the parameter space according to which vacua may persist in the UV theory, finding that in general there are regions in which none, one or many of the effective field theory vacua can be consistent with unitarity, causality and locality in the UV. Finally, we discuss the interplay between this map and cosmological observations. We find that the observationally favoured region of parameter space is incompatible with a large class of vacua, and conversely that particular boost-breaking vacua would imply positivity bounds that rule out otherwise observationally favoured cosmologies. We also identify a specific boost-breaking vacuum which is “closest” to the cosmological background, and show that the particular positivity bound we consider reduces the otherwise cosmologically favoured region of Galileon parameter space by up to 70 %, ruling out the vast majority of cosmologies with a positive coefficient for the cubic Galileon in the process.