428 research outputs found
The Rarita-Schwinger spin-3/2 equation in a nonuniform, central potential
The equations of motion for a massive spin-3/2 Rarita-Schwinger field in a
finite-range, central, Lorentz scalar potential are developed. It is shown that
the resulting density may not be everywhere positive definite.Comment: 9 pages, RevTe
Light Front Nuclear Physics: Toy Models, Static Sources and Tilted Light Front Coordinates
The principles behind the detailed results of a light-front mean field theory
of finite nuclei are elucidated by deriving the nucleon mode equation using a
simple general argument, based on the idea that a static source in equal time
coordinates corresponds to a moving source in light front coordinates. This
idea also allows us to solve several simple toy model examples: scalar field in
a box, 1+1 dimensional bag model, three-dimensional harmonic oscillator and the
Hulth\'en potential. The latter provide simplified versions of momentum
distributions and form factors of relevance to experiments. In particular, the
relativistic correction to the mean square radius of a nucleus is shown to be
very small. Solving these simple examples suggests another more general
approach-- the use of tilted light front coordinates. The simple examples are
made even simpler.Comment: 19 pages, references adde
Mechano-responsive polymer solutions based on CO2 supersaturation: shaking-induced phase transitions and self-assembly or dissociation of polymeric nanoparticles
Mechanical stimulation of supersaturated aqueous CO2 solutions is accompanied by a pH increase within seconds. In solutions of tailored homo- and AB diblock copolymers this is exploited to induce micelle formation, or, taking advantage of an aqueous upper critical solution temperature transition, nanoparticle disassembly
Nucleon Sigma Term and In-medium Quark Condensate in the Modified Quark-Meson Coupling Model
We evaluate the nucleon sigma term and in-medium quark condensate in the
modified quark-meson coupling model which features a density-dependent bag
constant. We obtain a nucleon sigma term consistent with its empirical value,
which requires a significant reduction of the bag constant in the nuclear
medium similar to those found in the previous works. The resulting in-medium
quark condensate at low densities agrees well with the model independent linear
order result. At higher densities, the magnitude of the in-medium quark
condensate tends to increase, indicating no tendency toward chiral symmetry
restoration.Comment: 9 pages, modified version to be publishe
gamma-Z corrections to forward-angle parity-violating e-p scattering
We use dispersion relations to evaluate the gamma-Z box contribution to
parity-violating electron scattering in the forward limit arising from the
axial-vector coupling at the electron vertex. The calculation makes full use of
the critical constraints from recent JLab data on electroproduction in the
resonance region as well as high energy data from HERA. At the kinematics of
the Qweak experiment, this gives a correction of 0.0047{+0.0011}{-0.0004}$ to
the Standard Model value 0.0713(8) of the proton weak charge. While the
magnitude of the correction is highly significant, the uncertainty is within
the anticipated experimental uncertainty of +- 0.003.Comment: 5 pages, 4 figures, expanded version to appear in Phys. Rev.
Light-Front Nuclear Physics: Mean Field Theory for Finite Nuclei
A light-front treatment for finite nuclei is developed from a relativistic
effective Lagrangian (QHD1) involving nucleons, scalar mesons and vector
mesons. We show that the necessary variational principle is a constrained one
which fixes the expectation value of the total momentum operator to be
the same as that for . This is the same as minimizing the sum of the total
momentum operators: . We obtain a new light-front version of the
equation that defines the single nucleon modes. The solutions of this equation
are approximately a non-trivial phase factor times certain solutions of the
usual equal-time Dirac equation. The ground state wave function is treated as a
meson-nucleon Fock state, and the meson fields are treated as expectation
values of field operators in that ground state. The resulting equations for
these expectation values are shown to be closely related to the usual meson
field equations. A new numerical technique to solve the self-consistent field
equations is introduced and applied to O and Ca. The computed
binding energies are essentially the same as for the usual equal-time theory.
The nucleon plus momentum distribution (probability for a nucleon to have a
given value of ) is obtained, and peaks for values of about seventy
percent of the nucleon mass. The mesonic component of the ground state wave
function is used to determine the scalar and vector meson momentum distribution
functions, with a result that the vector mesons carry about thirty percent of
the nuclear plus-momentum. The vector meson momentum distribution becomes more
concentrated at as increases.Comment: 36 pages, 2 figure
The Rarita-Schwinger Particles Under de Influence of Strong Magnetic Fields
In this work, we calculate the solutions of the Rarita-Schwinger equation
with the inclusion of the eletromagnetic interaction. Our gauge and coupling
prescription choices lead to Dirac-type solutions. One of the consequences of
our results are the Landau level occupation of particles, quite different from
the usual spin 1/2 particle system occupation numbers.Comment: 12 page
Quark Coulomb Interactions and the Mass Difference of Mirror Nuclei
We study the Okamoto-Nolen-Schiffer (ONS) anomaly in the binding energy of
mirror nuclei at high density by adding a single neutron or proton to a quark
gluon plasma. In this high-density limit we find an anomaly equal to two-thirds
of the Coulomb exchange energy of a proton. This effect is dominated by quark
electromagnetic interactions---rather than by the up-down quark mass
difference. At normal density we calculate the Coulomb energy of neutron matter
using a string-flip quark model. We find a nonzero Coulomb energy because of
the neutron's charged constituents. This effect could make a significant
contribution to the ONS anomaly.Comment: 4 pages, 2 figs. sub. to Phys. Rev. Let
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