Probing the holographic dilaton
Probing the holographic dilaton
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DOI：
10.1007/jhep06(2020)177
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发表时间：
2020-04
影响因子：
5.4
通讯作者：
Daniel Elander;M. Piai;John Roughley
中科院分区：
文献类型：
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作者：
Daniel Elander;M. Piai;John Roughley
许多强耦合场论承认规范不变束缚态谱，其中包括与真空具有相同量子数的标量粒子。挑战自然会出现，那就是如何描述它们。特别是，如何将膨胀子--与近似标度不变性相关的伪Nambu-Goldstone玻色子--与其他具有相同量子数的一般光标量区分开来？我们通过分析高维引力理论的涨落，在规范-引力对偶的背景下解决了这个问题。我们建议的诊断检验包括比较完整计算的结果，使用规范不变的整体涨落，与在探测近似下获得的结果。前者捕捉了标量自由度和度规自由度的混合，后者则手工去除了边界场论中产生膨胀算符的涨落。因此，探测器近似不能捕捉到可能的光伸缩子，而对于其他标量粒子，它应该表现得很好。我们在许多全息模型上测试了这一想法，其中一些最著名的完整重力背景是在自上而下构建的规范-重力二元性方法中构建的。我们计算了标量和张量涨落的谱，它们被解释为对偶场理论的束缚态(胶球)，我们重点介绍了探测近似产生接近正确物理结果的情况，以及出现显著差异的情况。我们将后一种情况解释为，用伸缩子识别最轻的标量态之一是合法的，至少是作为一种引导级近似。
Many strongly coupled field theories admit a spectrum of gauge-invariant bound states that includes scalar particles with the same quantum numbers as the vacuum. The challenge naturally arises of how to characterise them. In particular, how can a dilaton—the pseudo-Nambu-Goldstone boson associated with approximate scale invariance—be distinguished from other generic light scalars with the same quantum numbers? We address this problem within the context of gauge-gravity dualities, by analysing the fluctuations of the higher-dimensional gravitational theory. The diagnostic test that we propose consists of comparing the results of the complete calculation, performed by using gauge-invariant fluctuations in the bulk, with the results obtained in the probe approximation. While the former captures the mixing between scalar and metric degrees of freedom, the latter removes by hand the fluctuations that source the dilatation operator of the boundary field-theory. Hence, the probe approximation cannot capture a possible light dilaton, while it should fare well for other scalar particles. We test this idea on a number of holographic models, among which are some of the best known, complete gravity backgrounds constructed within the top-down approach to gauge-gravity dualities. We compute the spectra of scalar and tensor fluctuations, that are interpreted as bound states (glueballs) of the dual field theory, and we highlight those cases in which the probe approximation yields results close to the correct physical ones, as well as those cases where significant discrepancies emerge. We interpret the latter occurrence as an indication that identifying one of the lightest scalar states with the dilaton is legitimate, at least as a leading-order approximation.