623,958 research outputs found
Partial and Quasi Dynamical Symmetries in Nuclei
One of the interesting aspects in the study of atomic nuclei is the
strikingly regular behaviour many display in spite of being complex
quantum-mechanical systems, prompting the universal question of how regularity
emerges out of complexity. It is often conjectured that symmetries play a
pivotal role in our understanding of this emerging simplicity. But most
symmetries are likely to be broken, partial or both. Under such more realistic
conditions, does the concept of symmetry still provide a basis for our
understanding of regularity? I suggest that this requires the enlarged concepts
of partial and quasi dynamical symmetry.Comment: 5 pages, 5 figures, accepted for publication in Nuclear Physics New
Neutron-proton pairs in nuclei
A review is given of attempts to describe nuclear properties in terms of
neutron--proton pairs that are subsequently replaced by bosons. Some of the
standard approaches with low-spin pairs are recalled but the emphasis is on a
recently proposed framework with pairs of neutrons and protons with aligned
angular momentum. The analysis is carried out for general and applied to
nuclei in the and shells.Comment: 16 figures, 4 tables, accepted for publication in Int. J. of Modern
Physics
Harmonic Superspaces from Superstrings
We derive harmonic superspaces for N=2,3,4 SYM theory in four dimensions from
superstring theory. The pure spinors in ten dimensions are dimensionally
reduced and yield the harmonic coordinates. Two anticommuting BRST charges
implement Grassmann analyticity and harmonic analyticity. The string field
theory action produces the action and field equations for N=3 SYM theory in
harmonic superspace.Comment: 14 pp. Harvma
Seniority in quantum many-body systems
The use of the seniority quantum number in many-body systems is reviewed. A
brief summary is given of its introduction by Racah in the context of atomic
spectroscopy. Several extensions of Racah's original idea are discussed:
seniority for identical nucleons in a single- shell, its extension to the
case of many, non-degenerate shells and to systems with neutrons and
protons. To illustrate its usefulness to this day, a recent application of
seniority is presented in Bose--Einstein condensates of atoms with spin.Comment: 16 pages, 1 figure, accepted for publication in the Proceedings of
The American Institute of Physic
Absolute Time Derivatives
A four dimensional treatment of nonrelativistic space-time gives a natural
frame to deal with objective time derivatives. In this framework some well
known objective time derivatives of continuum mechanics appear as
Lie-derivatives. Their coordinatized forms depends on the tensorial properties
of the relevant physical quantities. We calculate the particular forms of
objective time derivatives for scalars, vectors, covectors and different second
order tensors from the point of view of a rotating observer. The relation of
substantial, material and objective time derivatives is treated.Comment: 26 pages, 4 figures (minor revision
Spatially Resolved Stellar Kinematics of Field Early-Type Galaxies at z=1: Evolution of the Rotation Rate
We use the spatial information of our previously published VLT/FORS2
absorption line spectroscopy to measure mean stellar velocity and velocity
dispersion profiles of 25 field early-type galaxies at a median redshift z=0.97
(full range 0.6<z<1.2). This provides the first detailed study of early-type
galaxy rotation at these redshifts. From surface brightness profiles from HST
imaging we calculate two-integral oblate axisymmetric Jeans equation models for
the observed kinematics. Fits to the data yield for each galaxy the degree of
rotational support and the mass-to-light ratio M/L_Jeans. S0 and Sa galaxies
are generally rotationally supported, whereas elliptical galaxies rotate less
rapidly or not at all. Down to M(B)=-19.5 (corrected for luminosity evolution),
we find no evidence for evolution in the fraction of rotating early-type (E+S0)
galaxies between z=1 (63+/-11%) and the present (61+/-5%). We interpret this as
evidence for little or no change in the field S0 fraction with redshift. We
compare M/L_Jeans with M/L_vir inferred from the virial theorem and globally
averaged quantities and assuming homologous evolution. There is good agreement
for non-rotating (mostly E) galaxies. However, for rotationally supported
galaxies (mostly S0) M/L_Jeans is on average ~40% higher than M/L_vir. We
discuss possible explanations and the implications for the evolution of M/L
between z=1 and the present and its dependence on mass.Comment: To appear in ApJ 683 (9 pages, 7 figures). Minor changes included to
match published versio
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