EPT Seminar

Mon, Feb 12, 2024 4:00 pm - 5:30 pm
PSC 3150


Speaker: Francesco Serra, JHU

Negativity, UV sensitivity and time-universality protection

I discuss two quantum mechanical effects that prevent violations of causality in low energy processes, even when faster-than-light propagation is possible. The first is a strong UV backreaction on any closed physical trajectory, similarly to what is found on Cauchy horizons in General Relativity. The second is a ghost instability that affects any configuration in which some excitations are classically seen propagating backwards in time. This instability causes a rapid decay to configurations in which the universality of the time direction is restored. These results show that faster-than-light propagation does not disrupt causal evolution, prompting to reconsider the role of microcausality and S-matrix analyticity in our description of nature.