Speaker
Description
I will demonstrate that opposite-sign kinetic terms are no obstruction for long-lived classical motion. I start with a class of polynomial point-particle models for which integrability allows to prove global stability despite the presence of opposite-sign kinetic terms and identify respective physical criteria for the interaction potential. I then generalise to (1+1) dimensional scalar field theories 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. Finally, I connect the above insights to recent progress concerning well-posed classical time evolution in higher-derivative theories of gravity. The latter opens up a novel pathway to access the strong-field regime in gravitational effective field theories. I look forward to discussing implications for cosmology.
