That special relativity restricts causal influences from propagating faster than the speed of light in a vacuum is a foundational principle of modern physics and common knowledge within the domain, requiring no citation.
The claim states a foundational postulate of special relativity: that the speed of light in a vacuum is the speed limit for causal influences. This is a defining principle of the theory and everyday knowledge in physics, making it common knowledge. Retrieved papers discuss nuances like detector models, approximations, or effective geometries where mathematical artifacts or specific conditions might appear to signal faster than light, but these do not alter the fundamental status of the physical law itself.