596 research outputs found
Instanton-like Excitations in 2D Fermionic Field Theory
New non-perturbatives excitations in the massless Thirring and Schwinger
models are discussed.Comment: Revtex, 9pp, to be published in New Trends in Theoretical Physic
Topological Excitations in the Thirring model
The quantization of the massless Thirring model in the light-cone using
functional methods is considered. The need to compactify the coordinate
in the light-cone spacetime implies that the quantum effective action for
left-handed fermions contains excitations similar to abelian instantons
produced by composite of left-handed fermions. Right-handed fermions don't have
a similar effective action. Thus, quantum mechanically, chiral symmetry must be
broken as a result of the topological excitations. The conserved charge
associated to the topological states is quantized. Different cases with only
fermionic excitations or bosonic excitations or both can occur depending on the
boundary conditions and the value of the coupling.Comment: title changed, one reference added, accepted in Phys. Lett.
Quantum Degenerate Systems
Degenerate dynamical systems are characterized by symplectic structures whose
rank is not constant throughout phase space. Their phase spaces are divided
into causally disconnected, nonoverlapping regions such that there are no
classical orbits connecting two different regions. Here the question of whether
this classical disconnectedness survives quantization is addressed. Our
conclusion is that in irreducible degenerate systems --in which the degeneracy
cannot be eliminated by redefining variables in the action--, the
disconnectedness is maintained in the quantum theory: there is no quantum
tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces
are boundaries separating distinct physical systems, not only classically, but
in the quantum realm as well. The relevance of this feature for gravitation and
Chern-Simons theories in higher dimensions cannot be overstated.Comment: 18 pages, no figure
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