Variational method in relativistic quantum field theory without cutoff

Relativistic Quantum Field Theory

Nonunitary Quantum Theory with a Field Cutoff

We consider a scalar quantum field theory, in which the interaction takes the form of a field cutoff; the energy diverges to infinity whenever the value of the field at some point falls outside a finite interval. In a simple (1+1)-dimensional version of this theory, we may calculate the results of certain scattering processes exactly. The main feature of the nontrivial solutions is the appearan...

Quasiparticle excitations in relativistic quantum field theory

We analyze the particle-like excitations arising in relativistic field theories in states different than the vacuum. The basic properties characterizing the quasiparticle propagation are studied using two different complementary methods. First we introduce a frequency-based approach, wherein the quasiparticle properties are deduced from the spectral analysis of the twopoint propagators. Second,...

Unstable Systems in Relativistic Quantum Field Theory

We show how the state of an unstable particle can be defined in terms of stable asymptotic states. This general definition is used to discuss and to solve some old problems connected with the short-time and large-time behaviour of the non-decay amplitude. CERN-TH/97-246 September 1997 ⋆ Address from Sept 1st, 1997 to August 31st, 1998.

8.324 Relativistic Quantum Field Theory II

The renormalization program has been shown to be a success operationally: 1. For a renormalizable theory, all ultraviolet divergences can be absorbed into redefinitions of bare quan­ tities, which are not observable. What is meant by the set of physical observables is unambiguous: it is well-defined in terms of a small number of physical couplings, masses and so forth. 2. The requirement of ren...