We investigate the interpulse thermal interaction of a train of ultrashort laser pulses and develop a model to describe the isobaric heating of air by a train of pulses undergoing filamentation. We calculate the heating of air from a single laser pulse and the resulting refractive index perturbation encountered by subsequent pulses, and use this to simulate the propagation of a high-power pulse train. The simulations show deflection of laser filaments by the thermal refractive index consistent with previous experimental measurements.
We explore a background-independent model of composite gravity. In a mean-field approximation, the vacuum expectation value of the composite metric satisfies Einstein’s equations (with corrections) as a consistency condition. A gravitational interaction then emerges in vacuum correlation functions. The action remains diffeomorphism invariant even as perturbation theory is organized about the dynamically selected vacuum spacetime. We discuss the role of nonphysical clock and rod fields in the analysis, the identification of physical observables, and the generalization to other theories including the standard model.
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