990 research outputs found
Highly excited negative parity baryons in the expansion
The masses of experimentally known highly excited baryons of negative parity
supposed to belong to the multiplets ( = 1,2,3) of
the band are calculated in the expansion method to order
by using a procedure which allows to considerably reduce the number of
linearly independent operators entering the mass formula. The numerical fits to
present data show that the coefficients encoding the QCD dynamics have large,
comparable values, for the flavor and spin operators. It implies that these
operators contribute dominantly to the flavor-spin SU(6) symmetry breaking,
like for the multiplet of the band.Comment: 15 pages, accepted for publication in Phys.Rev.
Quasi-Two-Body Decays of Nonstrange Baryons
We examine the decays of nonstrange baryons to the final states ,
, , , , , and
, in a relativized pair-creation() model which has
been developed in a previous study of the decays of the same baryon
states. As it is our goal to provide a guide for the possible discovery of new
baryon states at CEBAF and elsewhere, we examine the decays of resonances which
have already been seen in the partial-wave analyses, along with those of states
which are predicted by the quark model but which remain undiscovered. The level
of agreement between our calculation and the available widths from the
partial-wave analyses is encouraging.Comment: 41 pages, CEBAF-TH-93-1
Duality in Fractional Programming Involving Locally Arcwise Connected and Related Functions
A nonlinear fractional programming problem is considered, where the functions involved are diferentiable with respect to an arc.Necessary and su±cient optimality conditions are obtained in terms of the right diferentials with respect to an arc of the functions. A dual is formulated and duality results are proved using concepts of locally arcwise connected, locally Q-connected and locally P-connected functions .Our results generalize the results obtained by Lyall, Suneja and Aggarwal, Kaul and Lyall and Kaul et.al.Generalized convexity; Fractional programming; Optimality conditions, Duality
New Baryons in the Delta eta and Delta omega Channels
The decays of excited nonstrange baryons into the final states Delta eta and
Delta omega are examined in a relativized quark pair creation model. The
wavefunctions and parameters of the model are fixed by previous calculations of
N pi and N pi pi, etc., decays through various quasi-two body channels
including N eta and N omega. Our results show that the combination of
thresholds just below the region of interest and the isospin selectivity of
these channels should allow the discovery of several new baryons in such
experiments.Comment: 10 pages, RevTe
Interpretation of the Theta+ as an isotensor pentaquark with weakly decaying partners
The Theta+(1540), recently observed at LEPS, DIANA and CLAS, is hypothesized
to be an isotensor resonance. This implies the existence of a multiplet where
the Theta++, Theta+ and Theta0 have isospin-violating strong decays, and the
Theta+++ and Theta- have weak decays and so are long-lived. Production
mechanisms for these states are discussed. The J^P assignment of the Theta is
most likely 1/2^- or 3/2^-.Comment: references added, section on pentaquark model revised, 11 pages,
LaTeX, accepted for publication in Physics Letters
Strange Decays of Nonstrange Baryons
The strong decays of excited nonstrange baryons into the final states Lambda
K, Sigma K, and for the first time into Lambda(1405) K, Lambda(1520) K,
Sigma(1385) K, Lambda K*, and Sigma K*, are examined in a relativized quark
pair creation model. The wave functions and parameters of the model are fixed
by previous calculations of N pi and N pi pi, etc., decays. Our results show
that it should be possible to discover several new negative parity excited
baryons and confirm the discovery of several others by analyzing these final
states in kaon production experiments. We also establish clear predictions for
the relative strengths of certain states to decay to Lambda(1405) K and
Lambda(1520) K, which can be tested to determine if a three-quark model of the
Lambda(1405) K is valid. Our results compare favorably with the results of
partial wave analyses of the limited existing data for the Lambda K and Sigma K
channels. We do not find large Sigma K decay amplitudes for a substantial group
of predicted and weakly established negative-parity states, in contrast to the
only previous work to consider decays of these states into the strange final
states Lambda K and Sigma K.Comment: 25 pages, 8 figures, RevTe
Food security and migration in Africa: A validation of theoretical links using case studies from literature
The connection between food security and migration is increasingly discussed by both international agencies and academic literature. However, despite several improvements, we continue to know little about the complex causal-effect relations that link these aspects and, in particular, how much migration patterns are affected by food security issues and how much, as a feedback, migration can affect food security, on both the origin and destination areas. This paper aims firstly to draw a general framework of this nexus and then to validate it using empirical literature on the African continent. A few common points can be emphasized for the continent: due to structural and familiar characteristics, different strategies based on opportunity costs or risk minimization (including food security aspects) may emerge; individuals often migrate following household strategies; multi-nodal households are emerging; land grabbing and land tenure security represent important drivers to be considered; emergencies or critical situations often cause the erosion of women rights. In many situations, the poverty trap prevents most food insecure households to leave marginal lands
Magnetic moments of antidecuplet pentaquarks
We analyze the magnetic moment of the exotic pentaquarks of the flavor
antidecuplet in the constituent quark model for the case in which the ground
state is in an orbital L(p)=0(+) or a L(p)=1(-) state. We derive sum rules for
the magnetic moments. The magnetic moment of the Theta(1540) is found to be
0.38, 0.09 and 1.05 mu_N for J(p)=1/2(-), 1/2(+) and 3/2(+), respectively,
which is compared with the results obtained in other approaches.Comment: 15 pages, 1 figure, 3 tables. Revised version, extended introduction
and discussion, accepted for publication in Physics Letters
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