沿null测地线限定场 excursion 的边界及其在宇宙学中的应用
Bounding field excursions along null geodesics with applications to cosmology
AI总结：
本文推导了沿null测地线的标量场 excursion 限制，用于约束宇宙学中大场变化的范围，对anthropic场景有重要影响。
摘要：
在引力理论中，标量场通常存在于真空模空间中，其期望值的相干空间或时间变化可以产生可测量的引力效应。这种变化预计出现在从暴胀宇宙学到近极端黑洞近视界区域的多种情境中，其中它们可以弯曲光线并改变视界。本工作推导了一个关于标量场沿null测地线变化的定量场 excursion 限制（FEB），以膨胀参数表示。该限制源自Raychaudhuri方程，假设所有其他场满足null能量条件（NEC）。在某些包含类时裸奇点的时空中，该限制被饱和。提出了一种可能的推广，即到违反NEC但满足量子聚焦条件（QFC）加强版本的 semiclassical 时空。在宇宙学中，FEB限制大场 excursion 的范围，使其与e-folds数量线性相关，与暴胀模型无关。这在anthropic场景中具有显著影响，其中大 excursion 常被用来访问有利的真空。
英文摘要：
Scalar fields in theories of gravity often inhabit a moduli space of vacua, and coherent spatial or temporal variations in their expectation values can produce measurable gravitational effects. Such variations are expected in contexts ranging from inflationary cosmology to the near-horizon regions of near-extremal black holes, where they can deflect light rays and shift horizons. This work derives a quantitative field excursion bound (FEB) on scalar variations along null geodesics, expressed in terms of the expansion parameter. The bound follows from the Raychaudhuri equation, assuming that all other fields satisfy the null energy condition (NEC). It is saturated in certain spacetimes containing a timelike naked singularity. A possible generalization to semiclassical spacetimes that violate the NEC, but satisfy a strengthened version of the quantum focusing condition (QFC), is proposed. In cosmology, the FEB constrains the extent of large field excursions to be linearly bounded by the number of e-folds, independent of the inflationary model. This has notable implications for anthropic scenarios, where large excursions are often invoked to access favorable vacua.
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