4,221 research outputs found
Exotic solutions in string theory
Solutions of classical string theory, correspondent to the world sheets,
mapped in Minkowsky space with a fold, are considered. Typical processes for
them are creation of strings from vacuum, their recombination and annihilation.
These solutions violate positiveness of square of mass and Regge condition. In
quantum string theory these solutions correspond to physical states |DDF>+|sp>
with non-zero spurious component.Comment: accepted in Il Nuovo Cimento A for publication in 199
Henry F. Johnson, Professor of Law (1981-2008), St. Mary’s University School of Law
As a way to deal with his loss, this eulogy honors Henry Johnson (1942-2008) by focusing on ten good things about him. As a former English teacher, he valued clarity and precision, which reflects another good thing about Henry: the importance of strong organization. His zest for travel enabled him to share voluminous details about countless countries around the world, including where the best restaurants and wineries were. No description would be complete without emphasizing his love for golf, but the most important thing about Henry was the way he cared for his family, friends, and animals
Superintegrable systems with spin and second-order integrals of motion
We investigate a quantum nonrelativistic system describing the interaction of
two particles with spin 1/2 and spin 0, respectively. We assume that the
Hamiltonian is rotationally invariant and parity conserving and identify all
such systems which allow additional integrals of motion that are second order
matrix polynomials in the momenta. These integrals are assumed to be scalars,
pseudoscalars, vectors or axial vectors. Among the superintegrable systems
obtained, we mention a generalization of the Coulomb potential with scalar
potential and spin orbital one
.Comment: 32 page
Curve crossing in linear potential grids: the quasidegeneracy approximation
The quasidegeneracy approximation [V. A. Yurovsky, A. Ben-Reuven, P. S.
Julienne, and Y. B. Band, J. Phys. B {\bf 32}, 1845 (1999)] is used here to
evaluate transition amplitudes for the problem of curve crossing in linear
potential grids involving two sets of parallel potentials. The approximation
describes phenomena, such as counterintuitive transitions and saturation
(incomplete population transfer), not predictable by the assumption of
independent crossings. Also, a new kind of oscillations due to quantum
interference (different from the well-known St\"uckelberg oscillations) is
disclosed, and its nature discussed. The approximation can find applications in
many fields of physics, where multistate curve crossing problems occur.Comment: LaTeX, 8 pages, 8 PostScript figures, uses REVTeX and psfig,
submitted to Physical Review
`St\"uckelberg interferometry' with ultracold molecules
We report on the realization of a time-domain `St\"uckelberg interferometer',
which is based on the internal state structure of ultracold Feshbach molecules.
Two subsequent passages through a weak avoided crossing between two different
orbital angular momentum states in combination with a variable hold time lead
to high-contrast population oscillations. This allows for a precise
determination of the energy difference between the two molecular states. We
demonstrate a high degree of control over the interferometer dynamics. The
interferometric scheme provides new possibilities for precision measurements
with ultracold molecules.Comment: 4 pages, 5 figure
Analytic calculation of nonadiabatic transition probabilities from monodromy of differential equations
The nonadiabatic transition probabilities in the two-level systems are
calculated analytically by using the monodromy matrix determining the global
feature of the underlying differential equation. We study the time-dependent
2x2 Hamiltonian with the tanh-type plus sech-type energy difference and with
constant off-diagonal elements as an example to show the efficiency of the
monodromy approach. The application of this method to multi-level systems is
also discussed.Comment: 13 pages, 2 figure
Slow spin dynamics and quantum tunneling of magnetization in the dipolar antiferromagnet DyScO
We present a comprehensive study of static and dynamic magnetic properties in
the Ising-like dipolar antiferromagnet (AFM) DyScO\ by means of DC and AC
magnetization measurements supported by classical Monte-Carlo calculations. Our
AC-susceptibility data show that the magnetic dynamics exhibit a clear
crossover from an Arrhenius-like regime to quantum tunneling of magnetization
(QTM) at K. Below K DyScO orders in an
antiferromagnetic -type magnetic structure and the magnetization dynamics
slow down to the minute timescale. The low-temperature magnetization curves
exhibit complex hysteretic behavior, which depends strongly on the magnetic
field sweep rate. We demonstrate that the low-field anomalies on the
magnetization curve are related to the metamagnetic transition, while the
hysteresis at higher fields is induced by a strong magnetocaloric effect. Our
theoretical calculations, which take into account dipolar interaction between
Dy moments, reproduce essential features of the magnetic behavior of
DyScO. We demonstrate that DyScO represents a rare example of inorganic
compound, which exhibits QTM at a single-ion level and magnetic order due to
classical dipolar interaction
- …