The momentum of an electromagnetic wave inside a dielectric

The problem of assigning a momentum to an electromagnetic wave packet propagating inside an insulator has become known under the name of the Abraham-Minkowski controversy. In the present paper we re-examine the question, first through a power expansion in the polarizability of the medium and assuming the simplest and most natural choice for the force exerted on a dielectric material by an electromagnetic field. It is shown that the Abraham expression is highly favoured. We then show the complete generality of these results.Comment: 17 pages, no figure

Weak matrix elements and K-meson physics

An overview is presented about old and recent methods to compute the $K\to \pi \pi$ decay amplitude.Comment: 5 pages, talk presented at the XXXth International Conference on High Energy Physics (ICHEP 2000), July 27-August 2, 2000, Osaka, Japa

Boosted Statistical Mechanics

Based on the fundamental principles of Relativistic Quantum Mechanics, we give a rigorous, but completely elementary, proof of the relation between fundamental observables of a statistical system when measured relatively to two inertial reference frames, connected by a Lorentz transformation.Comment: 8 page

Some Considerations on Chiral Gauge Theories

Some general considerations on the problem of non-perturbative definition of Chiral Gauge Theories are presented.Comment: 13 pages, Latex, talk given at CHIRAL '99, Taipei, Sep. 13-18, 199

Heavy quark masses

In the large quark mass limit, an argument which identifies the mass of the heavy-light pseudoscalar or scalar bound state with the renormalized mass of the heavy quark is given. The following equation is discussed: m(sub Q) = m(sub B), where m(sub Q) and m(sub B) are respectively the mass of the heavy quark and the mass of the pseudoscalar bound state

q \bar q-potential

We show how to define and compute in a non-perturbative way the potential between q and \bar q colour sources in the singlet and octet (adjoint) representation of the colour group.Comment: 25 pages, REVTeX

Minkowski vacuum in background independent quantum gravity

We consider a local formalism in quantum field theory, in which no reference is made to infinitely extended spacial surfaces, infinite past or infinite future. This can be obtained in terms of a functional W[f,S] of the field f on a closed 3d surface S that bounds a finite region R of Minkowski spacetime. The dependence of W on S is governed by a local covariant generalization of the Schroedinger equation. Particles' scattering amplitudes that describe experiments conducted in the finite region R --the lab during a finite time-- can be expressed in terms of W. The dependence of W on the geometry of S expresses the dependence of the transition amplitudes on the relative location of the particle detectors. In a gravitational theory, background independence implies that W is independent from S. However, the detectors' relative location is still coded in the argument of W, because the geometry of the boundary surface is determined by the boundary value f of the gravitational field. This observation clarifies the physical meaning of the functional W defined by non perturbative formulations of quantum gravity, such as the spinfoam formalism. In particular, it suggests a way to derive particles' scattering amplitudes from a spinfoam model. In particular, we discuss the notion of vacuum in a generally covariant context. We distinguish the nonperturbative vacuum |0_S>, which codes the dynamics, from the Minkowski vacuum |0_M>, which is the state with no particles and is recovered by taking appropriate large values of the boundary metric. We derive a relation between the two vacuum states. We propose an explicit expression for computing the Minkowski vacuum from a spinfoam model.Comment: 8 pages, no figure