1,558 research outputs found
Gauge covariance and the fermion-photon vertex in three- and four- dimensional, massless quantum electrodynamics
In the quenched approximation, the gauge covariance properties of three
vertex Ans\"{a}tze in the Schwinger-Dyson equation for the fermion self energy
are analysed in three- and four- dimensional quantum electrodynamics. Based on
the Cornwall-Jackiw-Tomboulis effective action, it is inferred that the
spectral representation used for the vertex in the gauge technique cannot
support dynamical chiral symmetry breaking. A criterion for establishing
whether a given Ansatz can confer gauge covariance upon the Schwinger-Dyson
equation is presented and the Curtis and Pennington Ansatz is shown to satisfy
this constraint. We obtain an analytic solution of the Schwinger-Dyson equation
for quenched, massless three-dimensional quantum electrodynamics for arbitrary
values of the gauge parameter in the absence of dynamical chiral symmetry
breaking.Comment: 17 pages, PHY-7143-TH-93, REVTE
Dynamics of Toroidal Spiral Strings around Five-dimensional Black Holes
We examine the separability of the Nambu-Goto equation for test strings in a
shape of toroidal spiral in a five-dimensional Kerr-AdS black hole. In
particular, for a `{\it Hopf loop}\rq string which is a special class of the
toroidal spiral strings, we show the complete separation of variables occurs in
two cases, Kerr background and Kerr-AdS background with equal angular momenta.
We also obtain the dynamical solution for the Hopf loop around a black hole and
for the general toroidal spiral in Minkowski background.Comment: 16 pages, 1 figure, minor changes, references adde
The analytic structure of heavy quark propagators
The renormalised quark Dyson-Schwinger equation is studied in the limit of
the renormalised current heavy quark mass m_R --> infinity. We are particularly
interested in the analytic pole structure of the heavy quark propagator in the
complex momentum plane. Approximations in which the quark-gluon vertex is
modelled by either the bare vertex or the Ball-Chiu Ansatz, and the Landau
gauge gluon propagator takes either a gaussian form or a gaussian form with an
ultraviolet asymptotic tail are used.Comment: 21 pages Latex and 5 postscript figures. The original version of this
paper has been considerably extended to include a formalism dealing with the
renormalised heavy quark Dyson-Schwinger equation and uses a more realistic
Ansatz for the gluon propagator
Exactly solvable strings in Minkowski spacetime
We study the integrability of the equations of motion for the Nambu-Goto
strings with a cohomogeneity-one symmetry in Minkowski spacetime. A
cohomogeneity-one string has a world surface which is tangent to a Killing
vector field. By virtue of the Killing vector, the equations of motion can be
reduced to the geodesic equation in the orbit space. Cohomogeneity-one strings
are classified into seven classes (Types I to VII). We investigate the
integrability of the geodesic equations for all the classes and find that the
geodesic equations are integrable. For Types I to VI, the integrability comes
from the existence of Killing vectors on the orbit space which are the
projections of Killing vectors on Minkowski spacetime. For Type VII, the
integrability is related to a projected Killing vector and a nontrivial Killing
tensor on the orbit space. We also find that the geodesic equations of all
types are exactly solvable, and show the solutions.Comment: 11 pages, a reference added, some points clarifie
Off Mass Shell Effects in Hadron Electric Dipole Moments
We note that off the quark mass shell the operators
and , both of which reduce to
in the non-relativistic limit, are no longer
identical. In this paper we explore the effects of this difference in the
contribution of these quark electric moments to hadronic electric moments.Comment: 21 pages, 1 figure, Revtex, uses psfi
Survey of J=0,1 mesons in a Bethe-Salpeter approach
The Bethe-Salpeter equation is used to comprehensively study mesons with
J=0,1 and equal-mass constituents for quark masses from the chiral limit to the
b-quark mass. The survey contains masses of the ground states in all
corresponding J^{PC} channels including those with "exotic" quantum numbers.
The emphasis is put on each particular state's sensitivity to the low- and
intermediate-momentum, i.e., long-range part of the strong interaction.Comment: 8 pages, 4 figure
Collective synchronization in spatially extended systems of coupled oscillators with random frequencies
We study collective behavior of locally coupled limit-cycle oscillators with
random intrinsic frequencies, spatially extended over -dimensional
hypercubic lattices. Phase synchronization as well as frequency entrainment are
explored analytically in the linear (strong-coupling) regime and numerically in
the nonlinear (weak-coupling) regime. Our analysis shows that the oscillator
phases are always desynchronized up to , which implies the lower critical
dimension for phase synchronization. On the other hand, the
oscillators behave collectively in frequency (phase velocity) even in three
dimensions (), indicating that the lower critical dimension for frequency
entrainment is . Nonlinear effects due to periodic nature of
limit-cycle oscillators are found to become significant in the weak-coupling
regime: So-called {\em runaway oscillators} destroy the synchronized (ordered)
phase and there emerges a fully random (disordered) phase. Critical behavior
near the synchronization transition into the fully random phase is unveiled via
numerical investigation. Collective behavior of globally-coupled oscillators is
also examined and compared with that of locally coupled oscillators.Comment: 18 pages, 18 figure
Mass singularity and confining property in
We discuss the properties of the position space fermion propagator in three
dimensional QED which has been found previouly based on Ward-Takahashi-identity
for soft-photon emission vertex and spectral representation.There is a new type
of mass singularity which governs the long distance behaviour.It leads the
propagator vanish at large distance.This term corresponds to dynamical mass in
position space.Our model shows confining property and dynamical mass generation
for arbitrary coupling constant.Since we used dispersion retation in deriving
spectral function there is a physical mass which sets a mass scale.For finite
cut off we obtain the full propagator in the dispersion integral as a
superposition of different massses.Low energy behaviour of the proagator is
modified to decrease by position dependent mass.In the limit of zero infrared
cut-off the propagator vanishes with a new kind of infrared behaviour.Comment: 22pages,4figures,revtex4,Notational sloppiness are crrected.Submitted
to JHE
Neutron electric dipole moment: Constituent-dressing and compositeness
Contributions to the neutron's EDM, are calculated using a well-constrained
Ansatz for the nucleon's Poincare' covariant Fadde'ev amplitude. The
momentum-dependent quark dressing amplifies the contribution from the
current-quarks' EDMs; and dressed-quark confinement and binding make
distinguishable the effect of the two CP and T violating interactions: i
gamma_5 sigma_{mu nu} (p_1-p_2)_nu and gamma_5 (p_1+p_2)_mu, where p_{1,2} are
the current-quarks' momenta. The value of |d_n| obtained using the
current-quark EDMs generated by a minimal three Higgs doublet model of
spontaneous CP violation is close to the current experimental upper bound.Comment: 9 pages, LaTeX2e. Errors in Table 1 corrected; five references added.
To appear in Phys. Rev.
Pseudoscalar Meson Nonet at Zero and Finite Temperature
Theoretical understanding of experimental results from relativistic heavy-ion
collisions requires a microscopic approach to the behavior of QCD n-point
functions at finite temperatures, as given by the hierarchy of Dyson-Schwinger
equations, properly generalized within the Matsubara formalism. The convergence
of sums over Matsubara modes is studied. The technical complexity of
finite-temperature calculations mandates modeling. We present a model where the
QCD interaction in the infrared, nonperturbative domain, is modeled by a
separable form. Results for the mass spectrum of light quark flavors (u, d, s)
and for the pseudoscalar bound-state amplitudes at finite temperature are
presented.Comment: 14 pages, 11 figures, accepted for publication in Physics of
Particles and Nuclei Letters, based on invited lectures at "Dense Matter In
Heavy Ion Collisions and Astrophysics", 21.08-01.09 2006, Dubna, Russi
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