Wrong signs and causality protection in Effective Field Theory

Francesco Serra (Johns Hopkins University)

Wrong signs and causality protection in Effective Field Theory

Abstract

It has been shown that some Lorentz-invariant quantum field theories, such as those with higher-dimensional operators with negative coefficients, lead to superluminality on some classical backgrounds. While superluminality by itself is not logically inconsistent, these theories also predict the formation of causality-violating configurations at the classical level. I discuss how quantum mechanical effects alter the classical predictions of causality violation. Similarly to what is found in the chronology protection arguments of General Relativity, quantum mechanical effects from low energy quanta strongly backreact on such configurations, exciting unknown short-distance degrees of freedom and invalidating the classical predictions. Thus, there is no obvious *low-energy* obstruction to effective field theories with negative signs, Galileon symmetry, or a non-analytic S-matrix.

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