Algebraic fermion bosonization

By exploiting the construction of charged field algebras as canonical extensions of CCR current algebras in 1+1 dimensions and nonregular representations of extended algebras, we provide an algebraic construction of local Fermi fields as ultrastrong limits of bosonic variables in all representations which are locally Fock with respect to the ground-state representation of the massless scalar field.     

Chiral symmetry breaking and vacuum structure in QCD

The solution of the axial U(1) problem, the role of the topology of the gauge group in forcing the breaking of axial symmetry in any irreducible representation of the observable algebra and the θ vacua structure are revisited in the temporal gauge with attention to the mathematical consistency of the derivations. Both realizations with strong and weak Gauss law are discussed; the control of the general mechanisms and structures is obtained on the basis of the localization of the (large) gauge transformations and the local generation of the chiral symmetry. The Schwinger model in the temporal gauge exactly reproduces the general results.     

Hilbert space sectors,dynamical charges and spontaneous symmetry breaking in classical field theory

Results concerning existence and properties of Hilbert space sectors in the family of solutions of classical non-linear field equations are presented. Within this framework the existence of conserved dynamical charges and the occurrence of spontaneous symmetry breaking is discussed.     

The dipole field model

We provide a rigorous discussion of the dipole field model which significantly improves previous treatments and clarifies the general mathematical properties of the model as a prototype of four-dimensional QFT with confining infrared singularity. By exploiting the Krein-Hilbert structure associated with the local and covariant quantization of the model, we can characterize, in a simple way, the possible physical interpretation, prove that the breaking of spacetime translation is inevitable in the physical space (mechanisms of confinement), identify a nontrivial physical vacuum sector, and discuss the breaking of symmetries and the existence and role of translationally invariant field operators, etc.     

Locality,charges and quark confinement

General features of the Yang-Mills color theory suggested by Fritzsch, Gell-Mann and Leutwyler are discussed. It is shown that as a consequence of locality every observable is a color singlet and that the failure of the cluster property and consequently a q-$\text{q}$ potential not decreasing at infinity are possible, consistently with locality, just because of the non abelian gauge character. A generalized cluster property is proved for Yang-Mills local field theories.     

A Generalization of the Stone–Von Neumann Theorem to Nonregular Representations of the CCR-Algebra

We give a classification, up to unitary equivalence, of the representations of the C*-algebra of the Canonical Commutation Relations which generalizes the classical Stone–von Neumann Theorem to the case of representations which are strongly measurable, but not necessarily strongly continuous. The classification includes all the (nonregular) representations which have been considered in physical models.     

Relativistic Quantum Mechanics and Field Theory

The problems which arise for a relativistic quantum mechanics are reviewed and critically examined in connection with the foundations of quantum field theory. The conflict between the quantum mechanical Hilbert space structure, the locality property and the gauge invariance encoded in the Gauss' law is discussed in connection with the various quantization choices for gauge fields.     

Spectral stochastic processes arising in quantum mechanical models with a non-L 2 ground state

A functional integral representation is given for a large class of quantum mechanical models with a non-L ² ground state. As a prototype, the particle in a periodic potential is discussed: a unique ground state is shown to exist as a state on the Weyl algebra, and a functional measure (spectral stochastic process) is constructed on trajectories taking values in the spectrum of the maximal Abelian subalgebra of the Weyl algebra isomorphic to the algebra of almost periodic functions. The thermodynamical limit of the finite-volume functional integrals for such models is discussed, and the superselection sectors associated to an observable subalgebra of the Weyl algebra are described in terms of boundary conditions and/or topological terms in the finite-volume measures.Supported by DFG, Nr. Al 374/1-2     

Spontaneous symmetry breaking and energy gap generated by variables at infinity

Spontaneous symmetry breaking in the presence of long range instantaneous interactions is studied and the general mechanism underlying it is clarified. A characteristic feature is that the algebraic dynamics does not leave any essentially local algebra stable, i.e. variables at infinity get involved in the time evolution of local variables, so that in each irreducible representation the time evolution fails to be symmetric. For continuous symmetries, the Fourier transform of the vacuum expectation value of charge commutators is related to the energy spectrum at low momenta and a generalized Goldstone theorem is proved which explains the generation of energy gap. This energy gap is further shown to be governed by a classical dynamics at infinity, equivalently by the group generated by the effective Hamiltonian and the charge. Explicit examples are discussed.Work supported in part by INFN, Sezione di Pisa     

Some remarks on local operators in quantum electrodynamics

We assume the existence of a conserved current which generates locally gauge transformations of first kind. We are working in a local quantum Field Theory, where the fields are defined on a vector space where indefinite metric is allowed. We show that the Maxwell equations are not consistent with the above assumptions and the vectors obtained by applying local charged operators on the vacuum cannot describe physical states. Moreover we show that, if charged fields have non-trivial expectation value on the physical states, the vector space must contain vectors with negative norm. We discuss the relation between the local formulation of QED and a formulation in terms of physical states. As an example we study the transition from Gupta-Bleuler free QED to the Coulomb-gauge formulation.