48 research outputs found
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
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
Quantum description for a chiral condensate disoriented in a certain direction in isospace
We derive a quantum state of the disoriented chiral condensate dynamically,
considering small quantum fluctuations around a classical chiral condensate
disoriented in a certain direction in isospace. The obtained
nonisosinglet quantum state has the characteristic features; (i) it has the
form of the squeezed state, (ii) the state contains not only the component of
pion quanta in the direction but also the component in the
perpendicular direction to and (iii) the low momentum pions in the
state violate the isospin symmetry. With the quantum state, we calculate the
probability of the neutral fraction depending on the time and the pion's
momentum, and find that the probability has an unfamiliar form. For the low
momentum pions, the parametric resonance mechanism works with the result that
the probability of the neutral fraction becomes the well known form
approximately and that the charge fluctuation is small.Comment: 19 page
An Almost Perfect Quantum Lattice Action for Low-energy SU(2) Gluodynamics
We study various representations of infrared effective theory of SU(2)
Gluodynamics as a (quantum) perfect lattice action. In particular we derive a
monopole action and a string model of hadrons from SU(2) Gluodynamics. These
are lattice actions which give almost cut-off independent physical quantities
even on coarse lattices. The monopole action is determined by numerical
simulations in the infrared region of SU(2) Gluodynamics. The string model of
hadrons is derived from the monopole action by using BKT transformation. We
illustrate the method and evaluate physical quantities such as the string
tension and the mass of the lowest state of the glueball analytically using the
string model of hadrons. It turns out that the classical results in the string
model is near to the one in quantum SU(2) Gluodynamics.Comment: 39 pages, 10 figure
The System of Multi Color-flux-tubes in the Dual Ginzburg-Landau Theory
We study the system of multi color-flux-tubes in terms of the dual Ginzburg
-Landau theory. We consider two ideal cases, where the directions of all the
color-flux-tubes are the same in one case and alternative in the other case for
neighboring flux-tubes. We formulate the system of multi color-flux -tubes by
regarding it as the system of two color-flux-tubes penetrating through a two
dimensional sphere surface. We find the multi flux-tube configuration becomes
uniform above some critical flux-tube number density . On the other hand, the inhomogeneity on the color electric
distribution appears when the flux-tube density is smaller than . We
discuss the relation between the inhomogeneity in the color-electric
distribution and the flux-tube number density in the multi-flux-tube system
created during the QGP formation process in the ultra-relativistic heavy-ion
collision.Comment: 17 pages, Revtex, ( 7 figures - available on request from
[email protected]
QCD Phase Transition at Finite Temperature in the Dual Ginzburg-Landau Theory
We study the pure-gauge QCD phase transition at finite temperatures in the
dual Ginzburg-Landau theory, an effective theory of QCD based on the dual Higgs
mechanism. We formulate the effective potential at various temperatures by
introducing the quadratic source term, which is a new useful method to obtain
the effective potential in the negative-curvature region. Thermal effects
reduce the QCD-monopole condensate and bring a first-order deconfinement phase
transition. We find a large reduction of the self-interaction among
QCD-monopoles and the glueball masses near the critical temperature by
considering the temperature dependence of the self-interaction. We also
calculate the string tension at finite temperatures.Comment: 13 pages, uses PHYZZX ( 5 figures - available on request from
[email protected]
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