1,841 research outputs found
Extended non-chiral quark models confronting QCD
We discuss the low energy effective action of QCD in the quark sector. When
it is built at the CSB (chiral symmetry breaking) scale by means of
perturbation theory it has the structure of a generalized Nambu-Jona-Lasinio
(NJL) model with CSB due to attractive forces in the scalar channel. We show
that if the lowest scalar meson state is sufficiently lighter than the heavy
pseudoscalar then QCD favors a low-energy effective theory in which
higher dimensional operators (of the Nambu-Jona-Lasinio type) are dominated and
relatively strong. A light scalar quarkonium ( MeV)
would provide an evidence in favor to this NJL mechanism. Thus the non-chiral
Quasilocal Quark Models (QQM) in the dynamical symmetry-breaking regime are
considered as approximants for low-energy action of QCD. In the mean-field
(large-N_c) approach the equation on critical coupling surface is derived. The
mass spectrum of scalar and pseudoscalar excited states is calculated in
leading-log approach which is compatible with the truncation of the QCD
effective action with few higher-dimensional operators. The matching to QCD
based on the Chiral Symmetry Restoration sum rules is performed and it helps to
select out the relevant pattern of CSB as well as to enhance considerably the
predictability of this approach.Comment: 10 pages, Latex, talk at the Workshop HADRON 99, Coimbra, Portuga
Spontaneous parity violation in extreme conditions: an effective lagrangian analysis
We investigate how large baryon densities (and possibly high temperatures)
may induce spontaneous parity violation in the composite meson sector of
vector-like gauge theory (presumably QCD or techni-QCD) . The analysis at
intermediate energy scales is done by using an extended -model
lagrangian that includes two scalar and two pseudoscalar multiplets and
fulfills low-energy constraints for vector-like gauge theories. We elaborate on
a novel mechanism of parity breaking based on the interplay between lightest
and heavier meson condensates, which therefore cannot be realized in the
simplest model. The results are relevant for an idealized homogeneous
and infinite nuclear (quark or techniquark) matter where the influence of
density can be examined with the help of a constant chemical potential. The
model is able to describe satisfactorily the first-order phase transition to
stable nuclear matter, and predicts a second-order phase transition to a state
where parity is spontaneously broken. We argue that the parity breaking
phenomenon is quite generic when a large enough chemical potential is present.
Current quark masses are explicitly taken into account in this work and shown
not to change the general conclusions.Comment: 24 pages, substantial revisio
Classical Integrable 2-dim Models Inspired by SUSY Quantum Mechanics
A class of integrable 2-dim classical systems with integrals of motion of
fourth order in momenta is obtained from the quantum analogues with the help of
deformed SUSY algebra. With similar technique a new class of potentials
connected with Lax method is found which provides the integrability of
corresponding 2-dim hamiltonian systems. In addition, some integrable 2-dim
systems with potentials expressed in elliptic functions are explored.Comment: 19 pages, LaTeX, final version to be published in J.Phys.
Meson mass spectrum and OPE: matching to the large-N_c QCD
The relations between masses and decay constants of variety of meson
resonances in the energy range 0--3 GeV are verified from the string-like,
linear mass spectrum for vector, axial-vector, scalar and pseudoscalar mesons
with a universal slope. The way to match the universality with the Operator
Product Expansion (OPE) is proposed. The necessity of small deviations from
linearity in parameterization of the meson mass spectrum and their decay
constants is proven from matching to OPE.Comment: 4 pages, more refs added, Talk at V Int. Conference "Quark
Confinement and the Hadron Spectrum", 10-14 Sept. 2002, Garda Lake, Ital
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