Ghosts without Runaway Instabilities
Cédric Deffayet, Shinji Mukohyama, Alexander Vikman
Abstract
We present a simple class of mechanical models where a canonical degree of freedom interacts with another one with a negative kinetic term, i.e., with a ghost. We prove analytically that the classical motion of the system is completely stable for all initial conditions, notwithstanding that the conserved Hamiltonian is unbounded from below and above. This is fully supported by numerical computations. Systems with negative kinetic terms often appear in modern cosmology, quantum gravity, and high energy physics and are usually deemed as unstable. Our result demonstrates that for mechanical systems this common lore can be too naive and that living with ghosts can be stable.
Topics & Concepts
Kinetic energyPhysicsClassical mechanicsComputationMechanical systemKinetic termHamiltonian (control theory)QuantumCosmologySimple (philosophy)Theoretical physicsHamiltonian systemStatistical physicsQuantum mechanicsComputer scienceMathematicsPhilosophyArtificial intelligenceEpistemologyScalar fieldMathematical optimizationAlgorithmCosmology and Gravitation TheoriesBlack Holes and Theoretical PhysicsEarth Systems and Cosmic Evolution