标题： 沿零测地线的边界场偏差及其在宇宙学中的应用 显示英文标题

标题： Bounding field excursions along null geodesics with applications to cosmology

摘要： 标量场在引力理论中通常位于真空的模空间中，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。 这种变化在从暴胀宇宙学到近极端黑洞的近视界区域等各种情况下都可以预期，它们可以偏转光线并移动视界。 这项工作推导出一个标量变化沿类光测地线的定量场位移界限（FEB），该界限用膨胀参数表示。 该界限来源于Raychaudhuri方程，假设所有其他场都满足类空能量条件（NEC）。 在包含类时裸奇点的某些时空中，该界限被达到。 提出了一个可能的推广，适用于违反NEC但满足加强版量子聚焦条件（QFC）的半经典时空。 在宇宙学中，FEB将大场位移的范围限制为与e-fold数成线性关系，与暴胀模型无关。 这在人择场景中具有显著的意义，因为在这些场景中通常会引入大位移以访问有利的真空。 显示英文摘要

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.