447 research outputs found
Properties of the vector meson nonet at large N_c beyond the chiral limit
Masses and especially coupling constants of the vector meson nonet are
determined in the large-N_c limit, but beyond the chiral limit taking into
account terms up to quadratic order in the Goldstone boson masses. With two
input parameters five coupling constants for hadronic and dilepton decays are
determined which agree very well with the experimental results. The obtained
parameters are also used to calculate the pion and kaon decay constant in the
large-N_c limit. A consistent picture is only obtained, if the correct
assignment of the N_c-dependence of the electromagnetic charges of the quarks
is taken into account.Comment: 12 pages, strongly rewritten, more focussed on the central issu
Chromofields of Strings and Baryons
We calculate color electric fields of quark/antiquark () and 3
quark () systems within the chromodielectric model (CDM). We explicitly
evaluate the string tension of flux tubes in the --system and analyze
their profile. To reproduce results of lattice calculations we use a bag
pressure from which an effective strong coupling constant
follows. With these parameters we get a shaped
configuration for large --systems.Comment: Contributions to QNP 2002, Quarks and Nuclear Physics, Juelich,
Germany 3 pages, 10 eps figure
QCD sum rule analysis for light vector and axial-vector mesons in vacuum and nuclear matter
Extending previous work we study the constraints of QCD sum rules on mass and
width of light vector and axial-vector mesons in vacuum and in a medium with
finite nuclear density. For the latter case especially the effect of nuclear
pions leading to vector-axial-vector mixing is included in the analysis.Comment: RevTeX, 32 pages, 10 eps figure
Pressure-induced changes of the vibrational modes of spin-crossover complexes studied by nuclear resonance scattering of synchrotron radiation
Nuclear inelastic scattering (NIS) spectra were recorded for the
spin-crossover complexes STP and ETP (STP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg- ethane)](ClO4)2 and
ETP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg-butane)](ClO4)2) at
30 K and at room temperature and also at ambient pressure and applied pressure
(up to 2.6 GPa). Spin transition from the high-spin (HS) to the low-spin (LS)
state was observed by lowering temperature and also by applying pressure at
room temperature and has been assigned to the hardening of iron-bond stretching
modes due to the smaller volume in the LS isomer
Valence and magnetic instabilities in Sm compounds at high pressures
We report on the study of the response to high pressures of the electronic
and magnetic properties of several Sm-based compounds, which span at ambient
pressure the whole range of stable charge states between the divalent and the
trivalent. Our nuclear forward scattering of synchrotron radiation and specific
heat investigations show that in both golden SmS and SmB6 the pressure-induced
insulator to metal transitions (at 2 and about 4-7 GPa, respectively) are
associated with the onset of long-range magnetic order, stable up to at least
19 and 26 GPa, respectively. This long-range magnetic order, which is
characteristic of Sm(3+), appears already for a Sm valence near 2.7. Contrary
to these compounds, metallic Sm, which is trivalent at ambient pressure,
undergoes a series of pressure-induced structural phase transitions which are
associated with a progressive decrease of the ordered 4f moment.Comment: 15 pages (including 7 figures) submitted to J. Phys.: Condens. Matte
Interactions of multi-quark states in the chromodielectric model
We investigate 4-quark () systems as well as multi-quark
states with a large number of quarks and anti-quarks using the chromodielectric
model. In the former type of systems the flux distribution and the
corresponding energy of such systems for planar and non-planar geometries are
studied. From the comparison to the case of two independent -strings
we deduce the interaction potential between two strings. We find an attraction
between strings and a characteristic string flip if there are two degenerate
string combinations between the four particles. The interaction shows no strong
Van-der-Waals forces and the long range behavior of the potential is well
described by a Yukawa potential, which might be confirmed in future lattice
calculations. The multi-quark states develop an inhomogeneous porous structure
even for particle densities large compared to nuclear matter constituent quark
densities. We present first results of the dependence of the system on the
particle density pointing towards a percolation type of transition from a
hadronic matter phase to a quark matter phase. The critical energy density is
found at .Comment: 19 pages, 40 eps-figures, RevTex 4, v2: typos correcte
Nonequilibrium time evolution of the spectral function in quantum field theory
Transport or kinetic equations are often derived assuming a quasi-particle
(on-shell) representation of the spectral function. We investigate this
assumption using a three-loop approximation of the 2PI effective action in real
time, without a gradient expansion or on-shell approximation. For a scalar
field in 1+1 dimensions the nonlinear evolution, including the integration over
memory kernels, can be solved numerically. We find that a spectral function
approximately described by a nonzero width emerges dynamically. During the
nonequilibrium time evolution the Wigner transformed spectral function is
slowly varying, even in presence of strong qualitative changes in the effective
particle distribution. These results may be used to make further analytical
progress towards a quantum Boltzmann equation including off-shell effects and a
nonzero width.Comment: 20 pages with 6 eps figures, explanation and references added; to
appear in Phys.Rev.
On insertion-deletion systems over relational words
We introduce a new notion of a relational word as a finite totally ordered
set of positions endowed with three binary relations that describe which
positions are labeled by equal data, by unequal data and those having an
undefined relation between their labels. We define the operations of insertion
and deletion on relational words generalizing corresponding operations on
strings. We prove that the transitive and reflexive closure of these operations
has a decidable membership problem for the case of short insertion-deletion
rules (of size two/three and three/two). At the same time, we show that in the
general case such systems can produce a coding of any recursively enumerable
language leading to undecidabilty of reachability questions.Comment: 24 pages, 8 figure
Two- and three-body color flux tubes in the Chromo Dielectric Model
Using the framework of the Chromo Dielectric Model we perform an analysis of
color electric flux tubes in meson-like and baryon-like quark
configurations. We discuss the Abelian color structure of the model and point
out a symmetry in color space as a remnant of the SU(3) symmetry of QCD. The
generic features of the model are discussed by varying the model parameters. We
fix these parameters by reproducing the string tension MeV/fm and
the transverse width fm of the flux tube obtained in
lattice calculations. We use a bag constant MeV, a glueball
mass MeV and a strong coupling constant . We show that the asymptotic string profile of an infinitely long flux
tube is already reached for separations fm. A connection
to the Dual Color Superconductor is made by extracting a magnetic current from
the model equations and a qualitative agreement between the two descriptions of
confinement is shown. In the study of the system we observe a
-like geometry for the color electric fields and a
\textsf{Y}-like geometry in the scalar fields both in the energy density
distribution and in the corresponding potentials. The resulting total
potential is described neither by the -picture nor by the
\textsf{Y}-picture alone.Comment: 32 pages, 35 eps-figures, revised version, some references + 1
eps-file added, to be published in Phys.Rev.
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