21,651 research outputs found
Mesonic states in the generalised Nambu-Jona-Lasinio theories
For any Nambu-Jona-Lasinio model of QCD with arbitrary nonlocal,
instantaneous, quark current-current confining kernels, we use a generalised
Bogoliubov technique to go beyond BCS level (in the large-Nc limit) so as to
explicitly build quark-antiquark compound operators for creating/annihilating
mesons. In the Hamiltonian approach, the mesonic bound-state equations appear
(from the generalised Bogoliubov transformation) as mass-gap-like equations
which, in turn, ensure the absence, in the Hamiltonian, of mesonic Bogoliubov
anomalous terms. We go further to demonstrate the one-to-one correspondence
between Hamiltonian and Bethe-Salpeter approaches to non-local NJL-type models
for QCD and give the corresponding "dictionary" necessary to "translate" the
amplitudes built using the graphical Feynman rules to the terms of the
Hamiltonian, and vice versa. We comment on the problem of multiple vacua
existence in such type of models and argue that mesonic states in the theory
should be prescribed to have an extra index - the index of the replica in which
they are created. Then the completely diagonalised Hamiltonian should contain a
sum over this new index. The method is proved to be general and valid for any
instantaneous quark kernel.Comment: LaTeX2e, uses aipproc class, Talk given at the conference "Quark
Confinement and the Hadron Spectrum VI", 21-25 September 2004, Sardinia,
Italy, to appear in Proceeding
Quantum field theory approach to the vacuum replica in QCD
Quantum field theory is used to describe the contribution of possible new QCD
vacuum replica to hadronic processes. This sigma-like new state has been
recently shown to be likely to appear for any realistic four-quark interaction
kernel as a consequence of chiral symmetry. The local operator creating the
replica vacuum state is constructed explicitly. Applications to physical
processes are outlined.Comment: LaTeX2e, 2 EPS figures, uses ws-procs9x6 (included) and epsfig
classes, Talk given at the conference "Quark Confinement and the Hadron
Spectrum V", 10-14 September 2002, Gargnano, Italy, to appear in Proceeding
Chiral corrections to baryon properties with composite pions
A calculational scheme is developed to evaluate chiral corrections to
properties of composite baryons with composite pions. The composite baryons and
pions are bound states derived from a microscopic chiral quark model. The model
is amenable to standard many-body techniques such as the BCS and RPA
formalisms. An effective chiral model involving only hadronic degrees of
freedom is derived from the macroscopic quark model by projection onto hadron
states. Chiral loops are calculated using the effective hadronic Hamiltonian. A
simple microscopic confining interaction is used to illustrate the derivation
of the pion-nucleon form factor and the calculation of pionic self-energy
corrections to the nucleon and Delta(1232) masses.Comment: 29 pages, Revtex, 4 ps figure
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