The Origin and Fate of Rapid Negative Modes in Coleman--De Luccia Tunneling

Abstract: Coleman--De Luccia tunneling can exhibit an infinite tower of rapidly oscillating negative modes, complicating the semiclassical evaluation of the path integral. We show that this tower does not represent infinitely many bounce-specific instabilities, but instead is tied to a single underlying gravitational conformal sector. This sector is exposed in two different ways: by a large scalar gradient near the bubble wall and by the turning point of a compact Euclidean geometry. The corresponding conformal sector is already present in fluctuations about the false vacuum. Treating the bounce and the false vacuum in the same well-defined gauge and with a common regulator, we find that their high-frequency negative spectra approach one another. The ultraviolet tower therefore cancels from the relative negative-mode count, leaving a single bounce-specific negative mode. This clears a major conceptual obstacle toward a systematic calculation of the Coleman--De Luccia prefactor.