49,676 research outputs found
Searching for isovector signatures in the neutron-rich oxygen and calcium isotopes
We search for potential isovector signatures in the neutron-rich oxygen and
calcium isotopes within the framework of a relativistic mean-field theory with
an exact treatment of pairing correlations. To probe the isovector sector we
calibrate a few relativistic density functionals using the same isoscalar
constraints but with one differing isovector assumption. It is found that under
certain conditions, the isotopic chain in oxygen can be made to terminate at
the experimentally observed O isotope and in the case of the calcium
isotopes at Ca. To produce such behavior, the resulting symmetry
energy must be soft, with predicted values for the symmetry energy and its
slope at saturation density being MeV and
MeV, respectively. As a consequence, the neutron-skin
thickness of Pb is rather small: fm. This same model - labelled "FSUGarnet" -
predicts km for the radius of a "canonical"
1.4 neutron star, yet is also able to support a two-solar-mass
neutron star.Comment: 6 pages, 5 figure
Foldy-Wouthuysen transformation for a Dirac-Pauli dyon and the Thomas-Bargmann-Michel-Telegdi equation
The classical dynamics for a charged point particle with intrinsic spin is
governed by a relativistic Hamiltonian for the orbital motion and by the
Thomas-Bargmann-Michel-Telegdi equation for the precession of the spin. It is
natural to ask whether the classical Hamiltonian (with both the orbital and
spin parts) is consistent with that in the relativistic quantum theory for a
spin-1/2 charged particle, which is described by the Dirac equation. In the
low-energy limit, up to terms of the 7th order in ( and
is the particle mass), we investigate the Foldy-Wouthuysen (FW) transformation
of the Dirac Hamiltonian in the presence of homogeneous and static
electromagnetic fields and show that it is indeed in agreement with the
classical Hamiltonian with the gyromagnetic ratio being equal to 2. Through
electromagnetic duality, this result can be generalized for a spin-1/2 dyon,
which has both electric and magnetic charges and thus possesses both intrinsic
electric and magnetic dipole moments. Furthermore, the relativistic quantum
theory for a spin-1/2 dyon with arbitrary values of the gyromagnetic and
gyroelectric ratios can be described by the Dirac-Pauli equation, which is the
Dirac equation with augmentation for the anomalous electric and anomalous
magnetic dipole moments. The FW transformation of the Dirac-Pauli Hamiltonian
is shown, up to the 7th order again, to be also in accord with the classical
Hamiltonian.Comment: 18 page
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