227 research outputs found
Loosely bound hyperons in the SU(3) Skyrme model
Hyperon pairs bound in deuteron like states are obtained within the SU(3)
Skyrme model in agreement with general expectations from boson exchange models.
The central binding from the flavor symmetry breaking terms increases with the
strangeness contents of the interacting baryons whereas the kinetic non-linear
-model term fixes the spin and isospin of the bound pair. We give a
complete account of the interactions of octet baryons within the product
approximation to baryon number configurations.Comment: 35 pages REVTEX including 2 figs, with 3 further figs available on
request from [email protected] or from [email protected]
SI-94-TP3S2; STPHY-Th/94-
Quantum Corrections to Baryon Properties in Chiral Soliton Models
We present a procedure to calculate 1-loop graphs in the soliton sector of
chiral Lagrangians and use it to calculate quantum corrections to certain
baryon observables in Skyrme-type models. Results generally show an improvement
over the values obtained in tree approximation except for the case of the axial
coupling g_A.Comment: Chapters on magnetic polarizabilities and e.m. properties of Delta
isobar added, 90 pages, Latex, 9 Postscript figure
Fluctuation properties of strength functions associated with giant resonances
We performed fluctuation analysis by means of the local scaling dimension for
the strength function of the isoscalar (IS) and the isovector (IV) giant
quadrupole resonances (GQR) in Ca, where the strength functions are
obtained by the shell model calculation within up to the 2p2h configurations.
It is found that at small energy scale, fluctuation of the strength function
almost obeys the Gaussian orthogonal ensemble (GOE) random matrix theory limit.
On the other hand, we found a deviation from the GOE limit at the intermediate
energy scale about 1.7MeV for the IS and at 0.9MeV for the IV. The results
imply that different types of fluctuations coexist at different energy scales.
Detailed analysis strongly suggests that GOE fluctuation at small energy scale
is due to the complicated nature of 2p2h states and that fluctuation at the
intermediate energy scale is associated with the spreading width of the
Tamm-Dancoff 1p1h states.Comment: 14 pages including 13figure
Mass and width of the resonance in nuclei
We calculated the mass and width of the resonance inside nuclei within a
nucleon- model by including the self-energy of the in the
propagator. We found that in the nuclear medium the width of the
is increased by one order of magnitude while its mass changes only by a few
MeV. This broadening of the width of the resonance embedded in nuclei is
consistent with the experimental observations so that the can be
understood as a resonance. Thus, given the freedom between either
isospin 0 or isospin 2 for the , our results give weigth to the isospin-2
assignment.Comment: 14 pages, RevteX type, 2 eps figures. To be published in Phys. Rev. C
(September
Heterogeneity of proliferative markers in pancreatic β-cells of patients with severe hypoglycemia following Roux-en-Y gastric bypass.
Severe postprandial hypoglycemia with neuroglycopenia is an increasingly recognized, debilitating complication of Roux-en-Y gastric bypass (RYGB) surgery. Increased secretion of insulin and incretin hormones is implicated in its pathogenesis. Histopathologic examination of pancreas has demonstrated increased islet size and/or nuclear diameter in post-RYGB patients who underwent pancreatectomy for severe refractory hypoglycemia with neuroglycopenia (RYGB + NG). We aimed to determine whether β-cell proliferation or apoptosis is altered in RYGB + NG.
We performed an observational study to analyze markers of proliferation, apoptosis, cell cycle, and transcription factor expression in pancreatic tissue from affected RYGB + NG patients (n = 12), normoglycemic patients undergoing pancreatic surgery for benign lesions (controls, n = 6), and individuals with hypoglycemia due to insulinoma (n = 52).
Proliferative cell nuclear antigen (PCNA) expression was increased in insulin-positive cells in RYGB + NG patients (4.5-fold increase, p < 0.001 vs. controls) and correlated with β-cell mass. Ki-67 immunoreactivity was low in both RYGB + NG and controls, but did not differ between groups. Phospho-histone H3 levels did not differ between RYGB + NG and controls. PCNA and Ki-67 were both significantly lower in both controls and RYGB + NG than insulinomas. Markers of apoptosis and cell cycle (M30, p27, and p21) did not differ between groups. PDX1 and menin exhibited similar expression patterns, while FOXO1 appeared to be more cytosolic in RYGB + NG.
Markers of proliferation are heterogeneous in patients with severe post-RYGB hypoglycemia. Increased β-cell proliferation in some individuals may contribute to increased β-cell mass observed in severely affected patients
Hot Nucleons in Chiral Soliton Models
Chiral lagrangians as effective field theories of QCD are most suitable for
the study of nucleons in a hot pion gas because they contain pions and also
baryons as solitons of the same action. The semiclassical treatment of the
soliton solutions must be augmented by pionic fluctuations which requires
renormalisation to 1-loop, and finite temperatures do not introduce new
ultraviolet divergencies and may easily be considered. Alternatively, a
renormalisation scheme based on the renormalisation group equation at finite
temperature comprises and extends the rigorous results of chiral perturbation
theory and renders the low energy constants temperature-dependent which allows
the construction of temperature-dependent solitons below the critical
temperature. The temperature-dependence of the baryon energy and the
pion-nucleon coupling is studied. There is no simple scaling law for the
temperature-dependence of these quantities.Comment: 17 pages (RevTeX), 5 figure
Semiclassical quantization of SU(3) skyrmions
Semiclassical quantization of the SU(3)-skyrmions is performed by means of
the collective coordinate method. The quantization condition known for the
SU(2)-solitons quantized with SU(3) collective coordinates is generalized for
the SU(3) skyrmions with strangeness content different from zero. Quantization
of the dipole-type configuration with large strangeness content found recently
is considered as an example, the spectrum and the mass splitting of the
quantized states are estimated. The energy and baryon number density of SU(3)
skyrmions are presented in the form emphasizing their symmetry in different
SU(2) subgroups of SU(3), and the lower boundary for the static energy of SU(3)
skyrmions is derived.Comment: 16 pages, 2 figures (available upon request). Submitted to JETP on
May 6, 1997; in print. A preliminary short version of this paper is
hep-th/960916
Twist Mode in Spherical Alkali Metal Clusters
A remarkable orbital quadrupole magnetic resonance, so-called twist mode, is
predicted in alkali metal clusters where it is represented by
low-energy excitations of valence electrons with strong M2 transitions to the
ground state. We treat the twist by both macroscopic and microscopic ways. In
the latter case, the shell structure of clusters is fully exploited, which is
crucial for the considered size region (). The
energy-weighted sum rule is derived for the pseudo-Hamiltonian. In medium and
heavy spherical clusters the twist dominates over its spin-dipole counterpart
and becomes the most strong multipole magnetic mode.Comment: 8 pages, 4 figures, to be published in Phys. Rev. Lett., v.85, n.15,
200
Escape and Spreading Properties of Charge-Exchange Resonances in Bi 208
The properties of charge-exchange excitations of Pb with , i.e., the isobaric analog and Gamow-Teller resonances, are studied within
a self-consistent model making use of an effective force of the Skyrme type.
The well-known isobaric analog case is used to assess the reliability of the
model. The calculated properties of the Gamow-Teller resonance are compared
with recent experimental measurements with the aim of better understanding the
microscopic structure of this mode.Comment: 26 pages including references, figure captions and tables. Figures
are available upon request at [email protected] (decnet 32858::COLO).
Preprint code: IPNO/TH 94-2
Electro-Magnetic Nucleon Form Factors and their Spectral Functions in Soliton Models
It is demonstrated that in simple soliton models essential features of the
electro-magnetic nucleon form factors observed over three orders of magnitude
in momentum transfer are naturally reproduced. The analysis shows that
three basic ingredients are required: an extended object, partial coupling to
vector mesons, and relativistic recoil corrections. We use for the extended
object the standard skyrmion, one vector meson propagator for both isospin
channels, and the relativistic boost to the Breit frame. Continuation to
timelike leads to quite stable results for the spectral functions in the
regime from the 2- or 3-pion threshold to about two rho masses. Especially the
onset of the continuous part of the spectral functions at threshold can be
reliably determined and there are strong analogies to the results imposed on
dispersion theoretic approaches by the unitarity constraint.Comment: 24 pages, (RevTeX), 5 PS-figures; Data points in fig.2 and
corresponding references added. Final version, to be published in Z.Physik
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