Superluminality and UV Completion
| dc.creator | Shore, G. M. | |
| dc.date | 2007-01-19 | |
| dc.date.accessioned | 2026-07-07T10:38:07Z | |
| dc.date.available | 2026-07-07T10:38:07Z | |
| dc.description | The idea that the existence of a consistent UV completion satisfying the fundamental axioms of local quantum field theory or string theory may impose positivity constraints on the couplings of the leading irrelevant operators in a low-energy effective field theory is critically discussed. Violation of these constraints implies superluminal propagation, in the sense that the low-frequency limit of the phase velocity $v_{\rm ph}(0)$ exceeds $c$. It is explained why causality is related not to $v_{\rm ph}(0)$ but to the high-frequency limit $v_{\rm ph}(\infty)$ and how these are related by the Kramers-Kronig dispersion relation, depending on the sign of the imaginary part of the refractive index $\Ima n(\w)$ which is normally assumed positive. Superluminal propagation and its relation to UV completion is investigated in detail in three theories: QED in a background electromagnetic field, where the full dispersion relation for $n(\w)$ is evaluated numerically for the first time and the role of the null energy condition $T_{\m\n}k^\m k^\n \ge 0$ is highlighted; QED in a background gravitational field, where examples of superluminal low-frequency phase velocities arise in violation of the positivity constraints; and light propagation in coupled laser-atom $Ł$-systems exhibiting Raman gain lines with $\Ima n(\w) < 0$. The possibility that a negative $\Ima n(\w)$ must occur in quantum field theories involving gravity to avoid causality violation, and the implications for the relation of IR effective field theories to their UV completion, are carefully analysed. | |
| dc.description | 42 pages, 14 figures | |
| dc.identifier | https://arxiv.org/abs/hep-th/0701185 | |
| dc.identifier | http://arxiv.org/abs/hep-th/0701185 | |
| dc.identifier | Nucl.Phys.B778:219-258,2007 | |
| dc.identifier | doi:10.1016/j.nuclphysb.2007.03.034 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/180606 | |
| dc.subject | High Energy Physics - Theory | |
| dc.subject | General Relativity and Quantum Cosmology | |
| dc.title | Superluminality and UV Completion | |
| dc.type | text |