论文标题
因果关系的限制在$ n $ qCD中与重力耦合
Causality Constraints in Large $N$ QCD Coupled to Gravity
论文作者
论文摘要
限制规格理论包含具有任意旋转的胶球和介子，这些颗粒在$ n $中变得可稳定。但是，当耦合到重力时，亚稳态的较高自旋颗粒与因果关系冲突。只有在重力相互作用伴随着涉及其他较高旋转状态的相互作用时，才能避免这种张力。这些较高的自旋状态可以来自QCD部门或重力部门，但是这两种决议都具有令人惊讶的含义。例如，QCD状态可以解决问题，因为QCD扇区和重力部门之间存在非平凡的混合，这要求所有颗粒与树级处的胶球相互作用。如果重力部门状态恢复因果关系，则重力部门的任何弱耦合的紫外线完成都必须具有许多弦乐特征，并且在弦尺度上具有上限。在重力是微弱耦合的假设下，这两种情况都意味着该理论在$ n \ gtrsim \ frac {m _ {\ rm pl}}} {λ_{\ rm qcd}} $，其中$λ_{\λ_{\ rm Qcd} $ conflins conflac {
Confining gauge theories contain glueballs and mesons with arbitrary spin, and these particles become metastable at large $N$. However, metastable higher spin particles, when coupled to gravity, are in conflict with causality. This tension can be avoided only if the gravitational interaction is accompanied by interactions involving other higher spin states well below the Planck scale $M_{\rm pl}$. These higher spin states can come from either the QCD sector or the gravity sector, but both these resolutions have some surprising implications. For example, QCD states can resolve the problem since there is a non-trivial mixing between the QCD sector and the gravity sector, requiring all particles to interact with glueballs at tree-level. If gravity sector states restore causality, any weakly coupled UV completion of the gravity-sector must have many stringy features, with an upper bound on the string scale. Under the assumption that gravity is weakly coupled, both scenarios imply that the theory has a stringy description above $N\gtrsim \frac{M_{\rm pl}}{Λ_{\rm QCD}}$, where $Λ_{\rm QCD}$ is the confinement scale.
