408 research outputs found
Direct Force In High Momentum Limit of QCD For Proton Physics
An explicit construction of the proton wave function is outlined in the high
momentum limit of QCD dominated by a direct force, one generated by
hooking the ends of a vertex to 3 distinct vertices, thus
making up a -shaped diagram (see fig.1). The high degree of symmetry
thus involved ensures that the wave function is a mixture of
and components, rather than the traditional and
type. Some results of this paradigm shift are offered.Comment: 6 pages, Presented at 4th International Symposium on Symmetries in
Subatomic Physics at NTU, Taipei, 200
MarKov-Yukawa Transversality On Covariant Null Plane: Pion Form Factor, Gauge Invariance And Lorentz Completion
The Markov-Yukawa Transversality Principle (MYTP) on a 2-body Bethe-Salpeter
kernel is formulated on a covariant Null Plane (NP) to reconstruct the 4D BS
wave function for 2 fermion quarks in terms of 3D entities that satisfy a 3D
BSE. This result is the null-plane counterpart of a 3D-4D interconnection for
the 2-body BS wave functions found earlier by imposing MYTP covariantly in the
instantaneous rest frame (termed CIA) of the composite. This formulation yields
a 3D BSE which is formally identical to its Covariant Instantaneity form, thus
fully preserving its spectral results, while ensuring full covariance. More
importantly, the reconstructed 4D vertex functions in the covariant null-plane
ensure that 4D quark-loops are now free from ill-defined time-like momentum
integrations (which had plagued the earlier CIA vertex functions), while a
simple prescription of `Lorentz completion' in the new description yields a
manifestly Lorentz-invariant result.This is illustrated for the pion and kaon
form factors with full QED gauge-invariance, showing a behaviour at
large , and `correct' slopes at small . This method is compared with
the Kadychevsky-Karmanov light-front formalism.Comment: 17 pages, Late
A Dynamical Principle For 3D-4D Interlinkage In Salpeter-like Equations
The half-century old Markov-Yukawa Transversality Principle () which
provides a theoretical rationale for the covariant instantaneous approximation
() that underlies all Salpeter-like equations, is generalized to a
covariant null-plane ansatz (). A common characteristic of both
formulations is an exact 3D-4D interlinkage of BS amplitudes which facilitates
a two-tier description: the 3D form for spectroscopy, and the 4D form for
transition amplitudes as 4D loop integrals. Some basic applications of
on the covariant null plane (quark mass function, vacuum condensates, and decay
constants) are given on the lines of earlier applications to these processes
under .
PACS: 03.65.-w ; 03.65.Co ; 11.10.Qr ; 11.10.St
Keywords: Markov-Yukawa Transversality Principle (); Salpeter-like eqs;
Cov Instantaneity Ansatz (); Cov Null-Plane Ansatz (); 3D-4D
interlinkage; Vertex function; 4D loopsComment: LaTeX file, 25 pages, to be published in Nuclear Phys.
Adjustment of the electric current in pulsar magnetospheres and origin of subpulse modulation
The subpulse modulation of pulsar radio emission goes to prove that the
plasma flow in the open field line tube breaks into isolated narrow streams. I
propose a model which attributes formation of streams to the process of the
electric current adjustment in the magnetosphere. A mismatch between the
magnetospheric current distribution and the current injected by the polar cap
accelerator gives rise to reverse plasma flows in the magnetosphere. The
reverse flow shields the electric field in the polar gap and thus shuts up the
plasma production process. I assume that a circulating system of streams is
formed such that the upward streams are produced in narrow gaps separated by
downward streams. The electric drift is small in this model because the
potential drop in narrow gaps is small. The gaps have to drift because by the
time a downward stream reaches the star surface and shields the electric field,
the corresponding gap has to shift. The transverse size of the streams is
determined by the condition that the potential drop in the gaps is sufficient
for the pair production. This yields the radius of the stream roughly 10% of
the polar cap radius, which makes it possible to fit in the observed
morphological features such as the "carousel" with 10-20 subbeams and the
system of the core - two nested cone beams.Comment: 8 pages, 1 figur
Phonon effects in molecular transistors: Quantum and classical treatment
We present a comprehensive theoretical treatment of the effect of
electron-phonon interactions in molecular transistors, including both quantal
and classical limits and we study both equilibrated and out of equilibrium
phonons. We present detailed results for conductance, noise and phonon
distribution in two regimes. One involves temperatures large as compared to the
rate of electronic transitions on and off the dot; in this limit our approach
yields classical rate equations, which are solved numerically for a wide range
of parameters. The other regime is that of low temperatures and weak
electron-phonon coupling where a perturbative approximation in the Keldysh
formulation can be applied. The interplay between the phonon-induced
renormalization of the density of states on the quantum dot and the
phonon-induced renormalization of the dot-lead coupling is found to be
important. Whether or not the phonons are able to equilibrate in a time rapid
compared to the transit time of an electron through the dot is found to affect
the conductance. Observable signatures of phonon equilibration are presented.
We also discuss the nature of the low-T to high-T crossover.Comment: 20 pages, 19 figures. Minor changes, version accepted for publication
in Phys. Rev.
Isospin-Violating Meson-Nucleon Vertices as an Alternate Mechanism of Charge-Symmetry Breaking
We compute isospin-violating meson-nucleon coupling constants and their
consequent charge-symmetry-breaking nucleon-nucleon potentials. The couplings
result from evaluating matrix elements of quark currents between nucleon states
in a nonrelativistic constituent quark model; the isospin violations arise from
the difference in the up and down constituent quark masses. We find, in
particular, that isospin violation in the omega-meson--nucleon vertex dominates
the class IV CSB potential obtained from these considerations. We evaluate the
resulting spin-singlet--triplet mixing angles, the quantities germane to the
difference of neutron and proton analyzing powers measured in elastic
scattering, and find them commensurate to those computed
originally using the on-shell value of the - mixing amplitude.
The use of the on-shell - mixing amplitude at has been
called into question; rather, the amplitude is zero in a wide class of models.
Our model possesses no contribution from - mixing at , and
we find that omega-meson exchange suffices to explain the measured
analyzing power difference~at~183 MeV.Comment: 20 pages, revtex, 3 uuencoded PostScript figure
Non-Abelian dynamics and heavy multiquarks, Steiner-tree confinement in hadron spectroscopy
A brief review is first presented of attempts to predict stable multiquark
states within current models of hadron spectroscopy. Then a model combining
flip-flop and connected Steiner trees is introduced and shown to lead to stable
multiquarks, in particular for some configurations involving several heavy
quarks and bearing exotic quantum numbers.Comment: 8 pages, 5 figures, Invited talk at the 21st European Conference on
Few-Body Problems in Physics, Salamanca, Spain, August 29th--September 3rd,
2010, to appear in the Proceedings, ed.~A.~Valcarce et al., to appear in
Few-Body Syste
Tri-meson-mixing of -- and -- in the light-cone quark model
The radiative transition form factors of the pseudoscalar mesons {,
, } and the vector mesons {, , } are restudied
with -- and -- in tri-meson-mixing
pattern, which is described by tri-mixing matrices in the light-cone
constituent quark model. The experimental transition decay widths are better
reproduced with tri-meson-mixing than previous results in a two-mixing-angle
scenario of only two-meson - mixing and - mixing.Comment: 8 pages, 6 figures, final version to appear in EPJ
A New Approach to the 3D Faddeev Equation for Three-Body Scattering
A novel approach to solve the Faddeev equation for three-body scattering at
arbitrary energies is proposed. This approach disentangles the complicated
singularity structure of the free three-nucleon propagator leading to the
moving and logarithmic singularities in standard treatments. The Faddeev
equation is formulated in momentum space and directly solved in terms of
momentum vectors without employing a partial wave decomposition. In its
simplest form the Faddeev equation for identical bosons, which we are using, is
an integral equation in five variables, magnitudes of relative momenta and
angles. The singularities of the free propagator and the deuteron propagator
are now both simple poles in two different momentum variables, and thus can
both be integrated with standard techniques.Comment: 8 pages, 1 figur
Effective Lagrangian Approach to the Theory of Eta Photoproduction in the Region
We investigate eta photoproduction in the resonance region
within the effective Lagrangian approach (ELA), wherein leading contributions
to the amplitude at the tree level are taken into account. These include the
nucleon Born terms and the leading -channel vector meson exchanges as the
non-resonant pieces. In addition, we consider five resonance contributions in
the - and - channel; besides the dominant , these are:
and . The amplitudes for the
and the photoproduction near threshold have significant
differences, even as they share common contributions, such as those of the
nucleon Born terms. Among these differences, the contribution to the
photoproduction of the -channel excitation of the is the most
significant. We find the off-shell properties of the spin-3/2 resonances to be
important in determining the background contributions. Fitting our effective
amplitude to the available data base allows us to extract the quantity
, characteristic of the
photoexcitation of the resonance and its decay into the
-nucleon channel, of interest to precise tests of hadron models. At the
photon point, we determine it to be from
the old data base, and from a
combination of old data base and new Bates data. We obtain the helicity
amplitude for to be from the old data base, and from the combination of the old data base and new Bates
data, compared with the results of the analysis of pion photoproduction
yielding , in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in
Phys. Rev.
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