1,428 research outputs found
Vector Mesons on the Light Front
We apply the light-front quantization to the Nambu--Jona-Lasinio model with
the vector interaction, and compute vector meson's mass and light-cone
wavefunction in the large N limit. Following the same procedure as in the
previous analyses for scalar and pseudo-scalar mesons, we derive the
bound-state equations of a q-qbar system in the vector channel. We include the
lowest order effects of the vector interaction. The resulting transverse and
longitudinal components of the bound-state equation look different from each
other. But eventually after imposing an appropriate cutoff, one finds these two
are identical, giving the same mass and the same (spin-independent) light-cone
wavefunction. Mass of the vector meson decreases as one increases the strength
of the vector interaction.Comment: 11 pages, 3 figures, discussion on the cutoff scheme changed, Fig.3
replaced, and one reference adde
Light-Front Realization of Chiral Symmetry Breaking
We discuss a description of chiral symmetry breaking in the light-front (LF)
formalism. Based on careful analyses of several models, we give clear answers
to the following three fundamental questions: (i) What is the difference
between the LF chiral transformation and the ordinary chiral transformation?
(ii) How does a gap equation for the chiral condensate emerge? (iii) What is
the consequence of the coexistence of a nonzero chiral condensate and the
trivial Fock vacuum? The answer to Question (i) is given through a classical
analysis of each model. Question (ii) is answered based on our recognition of
the importance of characteristic constraints, such as the zero-mode and
fermionic constraints. Question (iii) is intimately related to another
important problem, reconciliation of the nonzero chiral condensate and the
invariance of the vacuum under the LF chiral transformation. This and Question
(iii) are understood in terms of the modified chiral transformation laws of the
dependent variables. The characteristic ways in which the chiral symmetry
breaking is realized are that the chiral charge is no longer conserved and that
the transformation of the scalar and pseudoscalar fields is modified. We also
discuss other outcomes, such as the light-cone wave function of the
pseudoscalar meson in the Nambu-Jona-Lasinio model.Comment: 26 pages, no figure, REVTEX, Journal versio
Spontaneous Symmetry Breaking in Discretized Light-Cone Quantization
Spontaneous symmetry breaking of the light-front Gross-Neveu model is studied
in the framework of the discretized light-cone quantization. Introducing a
scalar auxiliary field and adding its kinetic term, we obtain a constraint on
the longitudinal zero mode of the scalar field. This zero-mode constraint is
solved by using the expansion. In the leading order, we find a nontrivial
solution which gives the fermion nonzero mass and thus breaks the discrete
symmetry of the model. It is essential for obtaining the nontrivial solution to
treat adequately an infrared divergence which appears in the continuum limit.
We also discuss the constituent picture of the model. The Fock vacuum is
trivial and an eigenstate of the light-cone Hamiltonian. In the large
limit, the Hamiltonian consists of the kinetic term of the fermion with dressed
mass and the interaction term of these fermions.Comment: 25 pages, Latex, no figures, to be published in Progress of
Theoretical Physic
Color Superconductivity in Dense QCD and Structure of Cooper Pairs
The two-flavor color superconductivity is examined over a wide range of
baryon density with a single model. To study the structural change of Cooper
pairs, quark correlation in the color superconductor is calculated both in the
momentum space and in the coordinate space. At extremely high baryon density,
our model becomes equivalent to the usual perturbative QCD treatment and the
gap is shown to have a sharp peak near the Fermi surface due to the
weak-coupling nature of QCD. On the other hand, the gap is a smooth function of
the momentum at lower densities due to strong color magnetic and electric
interactions. The size of the Cooper pair is shown to become comparable to the
averaged inter-quark distance at low densities, which indicates a crossover
from BCS to BEC (Bose-Einstein condensation) of tightly bound Cooper pairs may
take place at low density.Comment: 6 pages, 5 figures. Invited talk at the Joint CSSM/JHF Workshop on
Physics at Japan Hadron Facility (March 14-21, Adelaide, 2002
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