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SS25 – Abstract
Aaron Held
(Laboratoire de Physique de l'École Normale Supérieure (LPENS))
24.4.2025
Stability of ghostly interactions: From scalar models to black-hole binaries
I will demonstrate that opposite-sign kinetic terms are no obstruction for long-lived classical motion. In the first part, I will focus on integrable point-particle models and provide a proof of global stability despite the presence of opposite-sign kinetic terms. In the second part, I will discuss scalar field theories in (1+1) dimensions to clarify that (i) even the unquenched classical instability is not instantaneous, (ii) higher frequency modes become more not less stable, and (iii) heavy ghosts can be integrated out. Further, I will demonstrate how self-interactions can quench the instability and lead to longlived classical motion. In the third part, I will connect the above insights to recent progress concerning well-posed time evolution in higher-derivative gravity. The latter opens up a novel pathway to access the strong-field regime, simulate black-hole binaries, and extract gravitational waveforms in gravitational effective field theories.
