We calculate the tree-level bispectrum of the inflaton field perturbation directly from the field equations, and construct the corresponding fNL parameter. Our results agree with previous ones derived from the Lagrangian. We argue that quantum theory should only be used to calculate the correlators when they first become classical a few Hubble times after horizon exit, the classical evolution t...

The dynamics of the dilute electrons can be modeled by the fundamental Vlasov-PoissonBoltzmann system when the electrons interact with themselves through collisions in the selfconsistent electric field. In this paper, it is shown that any smooth initial perturbation of a given global Maxwellian leads to a unique global-in-time classical solution when either the mean free path is small or the ba...

The modular vector field plays an important role in the theory of Poisson manifolds and is intimately connected with the Poisson cohomology of the space. In this paper we investigate its significance in the theory of integrable systems. We illustrate in detail the case of the Toda lattice both in Flaschka and natural coordinates.

Given a classical r-matrix on a Poisson algebra, we show how to construct a natural family of compatible Poisson structures for the Hamiltonian formulation of Lax equations. Examples for which our formalism applies include the Benny hierachy, the dispersionless Toda lattice hierachy, the dispersionless KP and modified KP hierachies, the dispersionless Dym hierachy etc.