21,492 research outputs found
Charge Symmetry Violation in Nuclear Physics
The study of charge symmetry violation in nuclear physics is a potentially
enormous subject. Through a few topical examples we aim to show that it is not
a subject of peripheral interest but rather goes to the heart of our
understanding of hadronic systems.Comment: Invited talk at the Int. Conference on Weak and Electromagnetic
Interactions in Nuclei, Osaka, June 12-16 199
Algebraic Properties of Quandle Extensions and Values of Cocycle Knot Invariants
Quandle 2-cocycles define invariants of classical and virtual knots, and
extensions of quandles. We show that the quandle 2-cocycle invariant with
respect to a non-trivial -cocycle is constant, or takes some other
restricted form, for classical knots when the corresponding extensions satisfy
certain algebraic conditions. In particular, if an abelian extension is a
conjugation quandle, then the corresponding cocycle invariant is constant.
Specific examples are presented from the list of connected quandles of order
less than 48. Relations among various quandle epimorphisms involved are also
examined
Quark-Meson Coupling Model for a Nucleon
The quark-meson coupling model for a nucleon is considered. The model
describes a nucleon as an MIT bag, in which quarks are coupled to scalar and
vector mesons. A set of coupled equations for the quark and the meson fields
are obtained and are solved in a self-consistent way. It is shown that the mass
of a nucleon as a dressed MIT bag interacting with sigma- and omega-meson
fields significantly differs from the mass of a free MIT bag. A few sets of
model parameters are obtained so that the mass of a dressed MIT bag becomes the
nucleon mass. The results of our calculations imply that the self-energy of the
bag in the quark-meson coupling model is significant and needs to be considered
in doing the nuclear matter calculations.Comment: 3 figure
Dirac-Sobolev inequalities and estimates for the zero modes of massless Dirac operators
The paper analyses the decay of any zero modes that might exist for a
massless Dirac operator H:= \ba \cdot (1/i) \bgrad + Q, where is -matrix-valued and of order O(|\x|^{-1}) at infinity. The approach
is based on inversion with respect to the unit sphere in and
establishing embedding theorems for Dirac-Sobolev spaces of spinors which
are such that and lie in Comment: 11 page
Effect of nucleon structure variation on the longitudinal response function
Using the quark-meson coupling (QMC) model, we study the longitudinal
response function for quasielastic electron scattering from nuclear matter. In
QMC the coupling constant between the scalar () meson and the nucleon
is expected to decrease with increasing nuclear density, because of the
self-consistent modification of the structure of the nucleon. The reduction of
the coupling constant then leads to a smaller contribution from relativistic
RPA than in the Walecka model. However, since the electromagnetic form factors
of the in-medium nucleon are modified at the same time, the longitudinal
response function and the Coulomb sum are reduced by a total of about 20% in
comparison with the Hartree contribution. We find that the relativistic RPA and
the nucleon structure variation both contribute about fifty-fifty to the
reduction of the longitudinal response.Comment: 14 pages, including 3 ps file
Variation of hadron masses in finite nuclei
Using a self-consistent, Hartree description for both infinite nuclear matter
and finite nuclei based on a relativistic quark model (the quark-meson coupling
model), we investigate the variation of the masses of the non-strange vector
mesons, the hyperons and the nucleon in infinite nuclear matter and in finite
nuclei.Comment: 4 pages plus one ps file, to appear in Proc. of International
Symposium on Non-Nucleonic Degrees of Freedom Detected in Nucleus (NNDF '96)
at Osaka, Japa
Self-consistent description of finite nuclei based on a relativistic quark model
Relativistic Hartree equations for spherical nuclei have been derived from a
relativistic quark model of the structure of bound nucleons which interact
through the (self-consistent) exchange of scalar () and vector
( and ) mesons. The coupling constants and the mass of the
-meson are determined from the properties of symmetric nuclear matter
and the rms charge radius in Ca. Calculated properties of static,
closed-shell nuclei from O to Pb are compared with experimental
data and with results of Quantum Hadrodynamics (QHD). The dependence of the
results on the nucleon size and the quark mass is investigated. Several
possible extensions of the model are also discussed.Comment: 37 pages, 17 postscript figures are included, uses epsfig.sty,
uuencoded Z-compressed .tar file (uufiles
Dyadic Green's Functions and Guided Surface Waves for a Surface Conductivity Model of Graphene
An exact solution is obtained for the electromagnetic field due to an
electric current in the presence of a surface conductivity model of graphene.
The graphene is represented by an infinitesimally-thin, local and isotropic
two-sided conductivity surface. The field is obtained in terms of dyadic
Green's functions represented as Sommerfeld integrals. The solution of
plane-wave reflection and transmission is presented, and surface wave
propagation along graphene is studied via the poles of the Sommerfeld
integrals. For isolated graphene characterized by complex surface conductivity,
a proper transverse-electric (TE) surface wave exists if and only if the
imaginary part of conductivity is positive (associated with interband
conductivity), and a proper transverse-magnetic (TM) surface wave exists when
the imaginary part of conductivity is negative (associated with intraband
conductivity). By tuning the chemical potential at infrared frequencies, the
sign of the imaginary part of conductivity can be varied, allowing for some
control over surface wave properties.Comment: 9 figure
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