AI 中文总结
本综述研究由参数ν描述的5D背景，其在ν=0时对应AdS、ν=1时对应线性伸缩子，探讨线性伸缩子在粒子物理与膜世界宇宙学中的应用，指出相关带隙连续谱、暗物质候选体等结果。
AI 中文摘要
1999年，丽莎·兰德尔（Lisa Randall）和拉曼·桑卓姆（Raman Sundrum）在五维（5D）反德西特（AdS）背景中引入了弯曲的额外维度，以解决粒子物理中的规范层级问题。作为额外收获，人们发现了其在四维（4D）共形场论（CFT）方面的全息解释。有趣的是，另一种5D背景——线性伸缩子（LD），被发现具有小弦理论（Little String Theory）方面的全息解释。在本综述中，我们将展示一组由实参数ν参数化的5D背景如何推广这两种理论，特别是当ν=0时对应AdS，ν=1时对应LD。此外，在5D理论框架下，我们将探讨LD背景的应用：i）粒子物理：可将5D普朗克尺度降低到亚普朗克值；ii）膜世界宇宙学（BWC）：基于额外真空的出现，该真空以5D黑洞为特征。在所有情况中，我们都发现体传播场存在带隙连续谱，这与非粒子（unparticle）存在关联。对于BWC，我们还指出存在无压全息流体，其可作为暗物质（DM），与标准模型（SM）的相互作用微弱（仅引力作用），且在暴胀后通过冻入（freeze-in）机制生成，与热SM浴退耦。我们还指出另一种可能性：将DM识别为长寿命、弱相互作用的大质量引力子，即由引力子传播子自能的辐射修正产生的孤立共振。
英文摘要
A warped extra dimension in a five-dimensional (5D) anti-de Sitter (AdS) background was introduced in 1999 by Lisa Randall and Raman Sundrum to solve the gauge hierarchy problem in particle physics. As a bonus, a holographic interpretation in terms of four-dimensional (4D) conformal field theories (CFTs) was found. Interestingly enough, another 5D background, linear dilaton (LD), was found to have a holographic interpretation in terms of Little String Theory. In this review, we will show how a set of 5D backgrounds, parametrized in terms of a real parameter $ν$, generalizes both theories and gives rise, in particular, to AdS for $ν=0$ and to LD for $ν=1$. Furthermore, working in the 5D theory, we will consider applications of the LD background to: (i) particle physics, so that the 5D Planck scale can be lowered to sub-Planckian values, and (ii) Brane World Cosmology (BWC), based on the appearance of an extra vacuum characterized by a 5D black hole. In all cases, we find a gapped continuum for bulk propagating fields, which makes a connection with unparticles. In the case of BWC, we also point out the existence of a pressureless holographic fluid that could play the role of dark matter (DM), with feeble (gravitational) interactions with the Standard Model (SM), decoupled from the thermal SM bath, and generated by a freeze-in mechanism after inflation. We also point out the additional possibility of identifying DM with a long-lived, feebly interacting massive graviton, as an isolated resonance generated by radiative corrections to the continuum graviton propagator self-energy.
Comments37 pages, 5 figures, 2 tables; v2 typos corrected, added references, captions of figures 3, 4 and 5 improved, added discussions in Secs. 2.1, 2.2, 6.4 and 7. It matches the version published in Universe
