105 research outputs found
Flavored exotic multibaryons and hypernuclei in topological soliton models
The energies of baryon states with positive strangeness, or anti-charm
(-beauty) are estimated in chiral soliton approach, in the "rigid oscillator"
version of the bound state soliton model proposed by Klebanov and Westerberg.
Positive strangeness states can appear as relatively narrow nuclear levels
(Theta-hypernuclei), the states with heavy anti-flavors can be bound with
respect to strong interactions in the original Skyrme variant of the model (SK4
variant). The binding energies of anti-flavored states are estimated also in
the variant of the model with 6-th order term in chiral derivatives in the
lagrangian as solitons stabilizer (SK6 variant). The latter variant is less
attractive, and nuclear states with anti-charm or anti-beauty can be unstable
relative to strong interactions. The chances to get bound hypernuclei with
heavy antiflavors are greater within "nuclear variant" of the model with
rescaled model parameter (Skyrme constant e or e' decreased by ~30%) which is
expected to be valid for baryon numbers greater than B ~10. The rational map
approximation is used to describe multiskyrmions with baryon number up to ~30
and to calculate the quantities necessary for their quantization (moments of
inertia, sigma-term, etc.).Comment: 24 pages, 7 table
The influence of environmental forcing on biodiversity and extinction in a resource competition model
In this paper, we study a model of many species that compete, directly or indirectly, for a pool of common resources under the influence of periodic, stochastic, and/or chaotic environmental forcing. Using numerical simulations, we find the number and sequence of species going extinct when the community is initially packed with a large number of species of random initial densities. Thereby, any species with a density below a given threshold is regarded to be extinct
Strangeness, charm and bottom in a chiral quark-meson model
In this paper we investigate an SU(3) extension of the chiral quark-meson
model. The spectra of baryons with strangeness, charm and bottom are considered
within a "rigid oscillator" version of this model. The similarity between the
quark part of the Lagrangian in the model and the Wess-Zumino term in the
Skyrme model is noted. The binding energies of baryonic systems with baryon
number B=2 and 3 possessing strangeness or heavy flavor are estimated. The
results obtained are in good qualitative agreement with those obtained
previously in the topological soliton (Skyrme) model.Comment: 12 pages, no figures. Journal ref: submitted to Nucl.Phys.
A comprehensive search for the \Theta^+ pentaquark on the lattice
We study spin 1/2 isoscalar and isovector, even and odd parity candidates for
the pentaquark particle using large scale lattice QCD
simulations. Previous lattice works led to inconclusive results because so far
it has not been possible to unambiguously identify the known scattering
spectrum and tell whether additionally a genuine pentaquark state also exists.
Here we carry out this analysis using several possible wave functions
(operators). Linear combinations of those have a good chance of spanning both
the scattering and pentaquark states. Our operator basis is the largest in the
literature, and it also includes spatially non-trivial ones with unit orbital
angular momentum. The cross correlator we compute is 1414 with 60
non-vanishing elements. We can clearly distinguish the lowest scattering
state(s) in both parity channels up to above the expected location of the
pentaquark, but we find no trace of the latter. Based on that we conclude that
there are most probably no pentaquark bound states at our quark masses,
corresponding to =400--630 MeV. However, we cannot rule out the
existence of a pentaquark state at the physical quark mass corresponding to
=135 MeV or pentaquarks with a more exotic wave function.Comment: 18 pages, 2 figure
Measurement of the LT-asymmetry in \pi^0 electroproduction at the energy of the \Delta (1232) resonance
The reaction p(e,e'p)pi^0 has been studied at Q^2=0.2 (GeV/c)^2 in the region
of W=1232 MeV. From measurements left and right of q, cross section asymmetries
\rho_LT have been obtained in forward kinematics \rho_LT(\theta_\pi^0=20deg) =
(-11.68 +/- 2.36_stat +/- 2.36_sys)$ and backward kinematics
\rho_LT(\theta_\pi^0=160deg) =(12.18 +/- 0.27_stat +/- 0.82_sys). Multipole
ratios \Re(S_1+^* M_1+)/|M_1+|^2 and \Re(S_0+^* M_1+)/|M_1+|^2 were determined
in the framework of the MAID2003 model. The results are in agreement with older
data. The unusally strong negative \Re(S_0+^* M_1+)/|M_1+|^2 required to bring
also the result of Kalleicher et al. in accordance with the rest of the data is
almost excluded.Comment: 7 pages, 7 figures, 4 tables. Changed content. Accepted for
publication in EPJ
Multibaryons as Symmetric Multiskyrmions
We study non-adiabatic corrections to multibaryon systems within the bound
state approach to the SU(3) Skyrme model. We use approximate ansatze for the
static background fields based on rational maps which have the same symmetries
of the exact solutions. To determine the explicit form of the collective
Hamiltonians and wave functions we only make use of these symmetries. Thus, the
expressions obtained are also valid in the exact case. On the other hand, the
inertia parameters and hyperfine splitting constants we calculate do depend on
the detailed form of the ansatze and are, therefore, approximate. Using these
values we compute the low lying spectra of multibaryons with B <= 9 and
strangeness 0, -1 and -B. Finally, we show that the non-adiabatic corrections
do not affect the stability of the tetralambda and heptalambda found in a
previous work.Comment: 17 pages, RevTeX, no figure
Inhomogeneous Field Configurations and the Electroweak Phase Transition
We investigate the effects of inhomogeneous scalar field configurations on
the electroweak phase transition. For this purpose we calculate the leading
perturbative correction to the wave function correction term Z(\vph,T), i.e.,
the kinetic term in the effective action, for the electroweak Standard Model at
finite temperature and the top quark self--mass. Our finding for the fermionic
contribution to Z(\vph,T) is infra--red finite and disagrees with other
recent results. In general, neither the order of the phase transition nor the
temperature at which it occurs change, once Z(\vph,T) is included. But a
non--vanishing, positive (negative) Z(\vph,T) enhances (decreases) the
critical droplet surface tension and the strength of the phase transition. We
find that in the range of parameter space, which allows for a first--order
phase transition, the wave function correction term is negative --- indicating
a weaker phase transition --- and especially for small field values so large
that perturbation theory becomes unreliable.Comment: 23 pages of LaTeX + 3 PostScript figures included in uuencoded form,
FERMI-PUB-93/253-
Nucleon Structure Functions in the Three Flavor NJL Soliton Model
We study the relevance of strange degrees of freedom for nucleon structure
functions. For this purpose we employ the three flavor generalization of the
collective quantization approach to the chiral soliton of the bosonized
Nambu-Jona-Lasinio model. Contrary to many other soliton models the hadronic
tensor is tractable in this model. By applying the Bjorken limit to the
hadronic tensor we extract the leading twist contributions to the nucleon
structure functions at the low energy scale at which the model is assumed to
approximate QCD. After transforming to the infinite momentum frame and
performing the DGLAP evolution program to these structure functions we compare
with available data for deep inelastic electron-nucleon scattering.Comment: 33 pages, 14 eps-files included via epsfi
Charm and hidden charm scalar mesons in the nuclear medium
We study the renormalization of the properties of low lying charm and hidden
charm scalar mesons in a nuclear medium, concretely of the D_{s0}(2317) and the
theoretical hidden charm state X(3700). We find that for the D_{s0}(2317), with
negligible width at zero density, the width becomes about 100 MeV at normal
nuclear matter density, while in the case of the X(3700) the width becomes as
large as 200 MeV. We discuss the origin of this new width and trace it to
reactions occurring in the nucleus, while offering a guideline for future
experiments testing these changes. We also show how those medium modifications
will bring valuable information on the nature of the scalar resonances and the
mechanisms of the interaction of D mesons with nucleons and nuclei
The apparatus composition and architecture of Erismodus quadridactylus and the implications for element homology in prioniodinin conodonts
The apparatus composition and architecture of prioniodinin conodonts is poorly understood, largely because few prioniodinin taxa are represented by articulated oral feeding apparatuses (natural assemblages) in the fossil record, but also due to the highly variable gradational morphology of their constituent elements that makes apparatus reconstruction problematic. We describe here a natural assemblage of Erismodus quadridactylus (Stauffer), a prioniodinin, from the Sandbian (Late Ordovician) of North Dakota, USA. The assemblage demonstrates that the apparatus architecture of Erismodus is similar to those of late Palaeozoic prioniodinins namely, Kladognathus Rexroad and Hibbardella Bassler, but also has similarities with ozarkodinin apparatuses. In addition, there is evidence to suggest that E. quadridactylus shares topological similarities to balognathid architecture, with respect to the position of its inferred P elements. The apparatus composition and architecture presented here indicate that, at least with respect to the M–S array, an ‘ozarkodinin‐type’ bauplan is probably more widely representative across prioniodontids. The assemblage demonstrates that element morphotypes traditionally considered to lie within the S array are M elements, whereas others traditionally interpreted as P elements are found in the S array. These observations are used as a basis for refining concepts of element homology among prioniodinin conodonts and their closest relatives
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