1,245 research outputs found
Tensor charges of light baryons in the Infinite Momentum Frame
We have used the Chiral-Quark Soliton Model formulated in the Infinite
Momentum Frame to investigate the octet, decuplet and antidecuplet tensor
charges up to the 5Q level. Using flavor SU(3) symmetry we have obtained for
the proton and in fair agreement previous
model estimations. The 5Q allowed us to estimate also the strange contribution
to the proton tensor charge . All those values have been
obtained at the model scale Q^2=0.36 GeV^2.Comment: 16 pages, 5 figure
Multi-fermion states for heavy fermions bound via Higgs exchange
A possibility to produce bound states of several heavy fermions, which are
bound together due to the Higgs exchange, is examined. It is shown that for 12
fermions, 6 fermions and 6 antifermions, occupying the lowest S_{1/2} shell
this bound state cannot exist if the fermion mass is below the critical value,
which depends on the Higgs mass and is found to be restricted to 320 < m_{cr} <
410 Gev/c^2 for the Higgs mass in the interval 100 < m_{H}< 200 Gev/c^2. This
estimate is derived in the relativistic mean field approximation. The
corrections are estimated to be not able to reduce significantly the critical
value for the fermion mass. Consequently there exist no bound state for 12 top
quarks, and the only feasible hope to observe a bag of 12 fermions
experimentally should rely on possible existence of heavy fermions of the next,
fourth generations.Comment: 4 pages, 3 figure
Influence of Meson's Widths on Yukawa-like Potentials and Lattice Correlation Functions
Euclidean point-to-point propagators or wall-to-wall correlators related to
exchange by an unstable particle(sigma,rho,omega-mesons) are modified by
presence of particle width. In particular, the usual method of deriving
particle masses from logarithmic derivatives need to be modified. Similarly
Yukawa-like potentials of nuclear physics due to exchange of those mesons are
significantly modified since the coupling to the decay products is strong. For
example, the large distance asymptotic changes, exp(-M_{min} r), where M_{min}
is the sum of the decay product masses
(2 m_{\pi}, 2 m_{e}, 2 m_{\nu}). In the area M_{min}r<1the potential has a
long-range tail 1/r^3. Similar effects appear due to the virtual decays in the
elecroweak sector of the Standard model. The mixing via electron
loop gives the parity violation potential with the range , i.e. the
range of the weak interaction increases times
Electronic structure and optical properties of quantum confined lead-salt nanowires
In the framework of four-band envelope-function formalism, developed earlier
for spherical semiconductor nanocrystals, we study the electronic structure and
optical properties of quantum-confined lead-salt (PbSe and PbS) nanowires (NWs)
with a strong coupling between the conduction and the valence bands. We derive
spatial quantization equations, and calculate numerically energy levels of
spatially quantized states of a transverse electron motion in the plane
perpendicular to the NW axis, and electronic subbands developed due to a free
longitudinal motion along the NW axis. Using explicit expressions for
eigenfunctions of the electronic states, we also derive analytical expressions
for matrix elements of optical transitions and study selection rules for
interband absorption.
Next we study a two-particle problem with a conventional long-range Coulomb
interaction and an interparticle coupling via medium polarization. The obtained
results show that due to a large magnitude of the high-frequency dielectric
permittivity of PbSe material, and hence, a high dielectric NW/vacuum contrast,
the effective coupling via medium polarization significantly exceeds the
effective direct Coulomb coupling at all interparticle separations along the NW
axis. Furthermore, the strong coupling via medium polarization results in a
bound state of the longitudinal motion of the lowest-energy electron-hole pair
(a longitudinal exciton), while fast transverse motions of charge carriers
remain independent of each other.Comment: Some misprints and mistakes are correcte
Neutrino scattering on atomic electrons in searches for neutrino magnetic moment
The scattering of a neutrino on atomic electrons is considered in the
situation where the energy transferred to the electrons is comparable to the
characteristic atomic energies, as relevant to the current experimental search
for neutrino magnetic moment. The process is contributed by the standard
electroweak interaction as well as by the possible neutrino magnetic moment.
Quantum mechanical sum rules are derived for the inclusive cross section at a
fixed energy deposited in the atomic system, and it is shown that the
differential over the energy transfer cross section is given, modulo very small
corrections, by the same expression as for free electrons, once all possible
final states of the electronic system are taken into account. Thus the atomic
effects effectively cancel in the inclusive process.Comment: 7 pages. A clarifying illustrative example adde
Modeling the electron with Cosserat elasticity
We suggest an alternative mathematical model for the electron in dimension
1+2. We think of our (1+2)-dimensional spacetime as an elastic continuum whose
material points can experience no displacements, only rotations. This framework
is a special case of the Cosserat theory of elasticity. Rotations of material
points are described mathematically by attaching to each geometric point an
orthonormal basis which gives a field of orthonormal bases called the coframe.
As the dynamical variables (unknowns) of our theory we choose a coframe and a
density. We then add an extra (third) spatial dimension, extend our coframe and
density into dimension 1+3, choose a conformally invariant Lagrangian
proportional to axial torsion squared, roll up the extra dimension into a
circle so as to incorporate mass and return to our original (1+2)-dimensional
spacetime by separating out the extra coordinate. The main result of our paper
is the theorem stating that our model is equivalent to the Dirac equation in
dimension 1+2. In the process of analyzing our model we also establish an
abstract result, identifying a class of nonlinear second order partial
differential equations which reduce to pairs of linear first order equations
Electroexcitation of the Roper resonance in the relativistic quark models
The amplitudes of the transition gamma* N -> P11(1440) are calculated within
light-front relativistic quark model assuming that the P11(1440) is the first
radial excitation of the 3q ground state. The results are presented along with
the predictions obtained in other relativistic quark models. In comparison with
the previous calculations, we have extended the range of Q^2 up to 4.5 GeV^2 to
cover the kinematic interval of the forthcoming experimental data. Using
approach based on PCAC, we have checked the relative sign between quark model
predictions for the N and P11(1440) contributions to the pion electroproduction
found in previous investigations.Comment: 5 pages, 1 figure, accepted by PR
Handling the Handbag Diagram in Compton Scattering on the Proton
Poincare invariance, gauge invariance, conservation of parity and time
reversal invariance are respected in an impulse approximation evaluation of the
handbag diagram. Proton wave functions, previously constrained by comparison
with measured form factors, that incorporate the influence of quark transverse
and orbital angular momentum (and the corresponding violation of proton
helicity conservation) are used. Computed cross sections are found to be in
reasonably good agreement with early measurements. The helicity correlation
between the incident photon and outgoing proton, , is both large and
positive at back angles. For photon laboratory energies of 6 GeV, we find
that , , and that the polarization can be
large.Comment: 9 pages, 6 figures. Replacement fixes some typos, improves references
and figures. An error in Fig. 6 was corrected and related comments in the
text change
On the Physical Propagators of QED
The true variables in QED are the transverse photon components and Dirac's
physical electron, constructed out of the fermionic field and the longitudinal
components of the photon. We calculate the propagators in terms of these
variables to one loop and demonstrate their gauge invariance. The physical
electron propagator is shown not to suffer from infrared divergences in any
gauge. In general, all physical Green's functions are gauge invariant and
infrared-finite.Comment: 7 pages, 2 figures (not included, may be obtained from the authors),
MZ-TH/93-05, DIAS-STP-93-0
Cross-section and polarization of neutrino-produced 's made simple
Practical formulae are derived for the cross-section and polarization of the
lepton produced in deep-inelastic neutrino-nucleon scattering in the
frame of the simple quark-parton model.Comment: 10 pages, no figure
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