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The underlying mixing of scalar mesons is studied in ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ decay within a generalized linear sigma model of low-energy QCD, which contains two nonets of scalar mesons and two nonets of pseudoscalar mesons (a quark-antiquark nonet and a four-quark nonet). The model has been previously employed in various investigations of the underlying mixings among scalar mesons below and above 1 GeV (as well as those of their pseudoscalar chiral partners) and has provided a coherent global picture for the physical properties and quark substructure of these states. The potential of the model is defined in terms of two- and four-quark chiral nonets and based on the number of underlying quark and antiquark lines in each term in the potential, a criterion for limiting the number of terms at each order of calculation (and systematically further improving the results thereafter). At the leading order, which corresponds to neglecting terms in the potential with higher than eight quark and antiquark lines, the free parameters of the model have been previously fixed in detailed global fits to scalar and pseudoscalar experimental mass spectra below and above 1 GeV together with several low-energy parameters. In the present work, the same order of potential with fixed parameters is used to further explore the underlying mixings among scalar mesons in the ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ decay. It is found that the linear sigma model with only a single lowest-lying nonet is not accurate in predicting the decay width, but inclusion of the mixing of this nonet with the next-to-lowest-lying nonet, together with the effect of the final-state interaction of pions, significantly improves this prediction and agrees with the experiment up to about 1%. It is also shown that, while the prediction of the leading order of the generalized model for the Dalitz parameters is not close to the experiment, the model is able to give a reasonable prediction of the energy dependencies of the normalized decay amplitude squared and that this is expected to improve with further refinement of the complicated underlying mixings. Overall, this investigation provides further support for the global picture of scalar mesons: those below 1 GeV are predominantly four-quark states and significantly mix with those above 1 GeV, which are closer to the conventional p-wave quark-antiquark states.

Motivated by the 1/Nc expansion, we present a simple model of �� scattering as a sum of a current-algebra contact term and resonant pole exchanges. The model preserves crossing symmetry as well as unitarity up to 1.2 GeV . Key features include chiral dynamics, vector meson dominance, a broad low energy scalar (�) meson and a Ramsauer-Townsend mechanism for the understanding of the 980 MeV region. We discuss in detail the regularization (corresponding to rescattering effects) necessary to make all these nice features work.

In the large ${\mathit{N}}_{\mathit{c}}$ approximation to QCD, the leading \ensuremath{\pi}\ensuremath{\pi} scattering amplitude is expressed as the sum of an infinite number of tree diagrams. We investigate the possibility that an adequate approximation at energies up to somewhat more than 1 GeV can be made by keeping diagrams which involve the exchange of resonances in this energy range in addition to the simplest chiral contact terms. In this approach crossing symmetry is automatic but individual terms tend to drastically violate partial wave unitarity. We first note that the introduction of the \ensuremath{\rho} meson in a chirally invariant manner substantially delays the onset of drastic unitarity violation which would be present for the current algebra term alone. This suggests a possibility of local (in energy) cancellation which we then explore in a phenomenological way. We include exchanges of leading resonances up to the 1.3 GeV region. However, unitarity requires more structure which we model by a four derivative contact term or by a low-lying scalar resonance which is presumably subleading in the 1/${\mathit{N}}_{\mathit{c}}$ expansion, but may nevertheless be important. The latter two flavor model gives a reasonable description of the phase shift ${\mathrm{\ensuremath{\delta}}}_{0}^{0}$ up until around 860 MeV, before the effects associated with the KK\ifmmode\bar\else\textasciimacron\fi{} threshold come into play.

Pion pion scattering is studied in a generalized linear sigma model which contains two scalar nonets (one of quark-antiquark type and the other of diquark-antidiquark type) and two corresponding pseudoscalar nonets. An interesting feature concerns the mixing of the four isosinglet scalar mesons which yield poles in the scattering amplitude. Some realism is introduced by enforcing exact unitarity via the K-matrix method. It is shown that a reasonable agreement with experimental data is obtained up to about 1 GeV. The poles in the unitarized scattering amplitude are studied in some detail. The lowest pole clearly represents the sigma meson (or f0(600)) with a mass and decay width around 500 MeV. The second pole invites comparison with the f0(980) which has a mass around 1 GeV and decay width around 100 MeV. The third and fourth poles, resemble some of the isosinglet state in the complicated 1-2 GeV region. Some comparison is made to the situation in the usual SU(3) linear sigma model with a single scalar nonet.

The unusual multiplet structures associated with the light spin zero mesons have recently attracted a good deal of theoretical attention. Here we discuss some aspects associated with the possibility of getting new experimental information on this topic from semileptonic decays of heavy charged mesons into an isosinglet scalar or pseudoscalar plus leptons.

We give the general framework for adding "light" vector particles to the heavy hadron effective chiral Lagrangian. This has strong motivations both from the phenomenological and aesthetic standpoints. An application to the already observed $D \rightarrow \overbar{K^*} $ weak transition amplitude is discussed., Comment: 19 pages, LaTeX document

We investigate the heavy baryons which arise as solitonic excitations in a ``heavy meson" chiral Lagrangian which includes the light vector particles. It is found that the effect of the light vectors may be substantial. We also present a simple derivation which clearly shows the connection to the Callan-Klebanov approach., Comment: 13 pages; LaTex; SU-4240-532; UR 1306/ER-40685-755 (Minor typos corrected)

We further study a predictive model for the masses and mixing matrix of three Majorana neutrinos. At zeroth order the model yielded degenerate neutrinos and a generalized tribimaximal mixing matrix. At first order the mass splitting was incorporated and the tribimaximal mixing matrix emerged with very small corrections but with a zero value for the parameter ${s}_{13}$. In the present paper a different, assumed weaker, perturbation is included which gives a nonzero value for ${s}_{13}$ and further corrections to other quantities. These corrections are worked out and their consequences discussed under the simplifying assumption that the conventional $CP$ violation phase vanishes. It is shown that the existing measurements of the parameter ${s}_{23}$ provide strong bounds on ${s}_{13}$ in this model.

The size of the pion cloud in the Skyrme model is considered as a collective coordinate leading to a quantum-mechanical treatment of the size of a nucleonlike object. By evaluating the time evolution of a state possessing an initial size of the order inverse momentum transfer we investigate the approach to color transparency at momentum transfers up to about 1.5 GeV.

An exact solution is presented for the system of three Majorana neutrinos with arbitrary transition moments propagating in a uniformly twisting, transverse magnetic field. The characteristic new features compared to the two-neutrino case are emphasized.

The putative classical soliton in the minimal nonlinear {sigma} model (no Skyrme term) is known to be unstable to collapse. We note that the imposition of a short-distance cutoff (which is anyway physically reasonable for a nonrenormalizable model) yields a stable classical soliton. We further suggest that this cutoff, carrying as it does some implicit dynamical information, be treated as a quantized dynamical variable. The resulting one- (experimentally fixed) parameter model agrees with experiment roughly as well as the simple {sigma} model {ital with} the Skyrme term. We interpret this feature as an indication of the robustness of the description of the nucleon as being dominated by a hedgehog-type meson cloud. It is suggested that the same approach might be useful in some other situations where the long-distance description of the physics is more precisely known than is the short-distance description.

A generalized linear sigma model for low energy QCD is employed to study the quark structure of eight low lying scalar isomultiplets as well as eight low lying pseudoscalar isomultiplets. The model, building on earlier work, assumes the possible mixing of quark anti-quark states with others made of two quarks and two antiquarks. No {\it a priori} assumption is made about the quark contents of the states, which emerge as predictions. An amusing and contrasting pattern for the quark structure is found; the lighter conventional pseudoscalars are, as expected, primarily of two quark type whereas the lighter scalars have very large four quark admixtures. The new feature of the present paper compared to earlier ones in this series involves the somewhat subtle and complicated effects of SU(3) flavor breaking. They do not alter the general pattern of two quark vs. four quark mixing obtained in the SU(3)symmetric case but, of course, give a more detailed picture.

This study concerns the evolution of the information seeking and use models for professionals essentially, the information access practices. Coming from Anglo-Saxon literature, this new information science research trend, evolve with paradigms and different information seeking and use models have emerged, in order to explain how professional seeks information and what can be done in order to help them. Two main categories can be distinguished : the information seeking and use model versus the information retrieval model. So we will present today this diversity of models and we will evaluate them in order to see if a convergence is possible with the same vocabulary and procedures.

We present a detailed study of a linear sigma model containing one chiral nonet transforming under U(1)$_A$ as a quark-antiquark composite and another chiral nonet transforming as a diquark-anti diquark composite (or, equivalently from a symmetry point of view, as a two meson molecule). The model provides an intuitive explanation of a current puzzle in low energy QCD: Recent work has suggested the existence of a lighter than 1 GeV nonet of scalar mesons which behave like four quark composites. On the other hand, the validity of a spontaneously broken chiral symmetric description would suggest that these states be chiral partners of the light pseudoscalar mesons, which are two quark composites. The model solves the problem by starting with the two chiral nonets mentioned and allowing them to mix with each other. The input of physical masses in the SU(3) invariant limit for two scalar octets and an "excited" pion octet results in a mixing pattern wherein the light scalars have a large four quark content while the light pseudoscalars have a large two quark content. One light isosinglet scalar is exceptionally light. In addition, the pion pion scattering is also studied and the current algebra theorem is verified for massless pions which contain some four quark admixture., Comment: 22 pages, 8 figures

We attempt to improve the description of the strange baryons in the collective'' approach to quantizing the SU(3) Skyrme model. We go beyond the recent work of Yabu and Ando by employing a kind of cranking'' procedure for the strange fields, which allows them to contribute to the corresponding moment of inertia. A better overall fit to the mass differences of the low-lying 1/2{sup +} and 3/2{sup +} baryons is achieved using values of parameters fixed from the meson sector. The picture of the baryons that emerges is one in which they contain appreciably fewer {ital s{bar s}} current quark pairs'' than in a naive perturbation approach. At the constituent-quark level there is significant mixing of different SU(3) multiplets. This and a number of related points are treated.

As a preliminary we consider the phenomenology of the European Muon Collaboration experimental result without assuming SU(3) invariance. The most reliable conclusion is that the singlet axial-vector current matrix element is rather small. We calculate this matrix element in a variety of chiral-soliton models in which the axial anomaly equation is satisfied. There are a number of subtleties which we explore. It turns out that reasonable chiral models including only pseudoscalar fields give a zero matrix element. Taking "short-distance" effects consistently into account via the inclusion of vector mesons or explicit quarks does give a small nonzero result. The situation is closely analogous to the prediction of a nonzero result for the nonelectromagnetic part of the neutron-proton mass difference in these chiral models.

We propose a systematic procedure to study a generalized linear sigma model which can give a physical picture of possible mixing between qq and qqq q low lying spin zero states. In the limit of zero quark masses, we derive the model independent results for the properties of the Nambu-Goldstone pseudoscalar particles. For getting information on the scalars it is necessary to make a specific choice of terms. We impose two plausible physical criteria-the modeling of the axial anomaly and the suppression of effective vertices representing too many fermion lines-for limiting the large number of terms which are allowed on general grounds. We calculate the tree-level spectrum based on the leading terms in our approach and find that it prominently exhibits a very low mass isosinglet scalar state. Finally we point out that the low energy result for scattering of pions continues to hold in the general version of the model.

We further study the previously proposed Ansatz, Tr(M)=0, for a prediagonal light Majorana type neutrino mass matrix. If CP violation is neglected this enables one to use the existing data on squared mass differences to estimate (up to a discrete ambiguity)the neutrino masses themselves. If it is assumed that only the conventional CP phase is present, the ansatz enables us to estimate this phase in addition to all three masses. If it is assumed that only the two Majorana CP phases are present, the Ansatz enables us to obtain a one parameter family of solutions for the masses and phases. This enables us to obtain a simple "global" view of lepton number violation effects. Furthermore, using an SO(10) motivation for the Ansatz suggests an amusing toy (clone) model in which the heavy neutrinos have the same mixing pattern and mass ratios as the light ones. In this case only their overall mass scale is not known (although it is constrained by the initial motivation). Using this toy model we make a rough estimate of the baryon to photon ratio induced by the leptogenesis mechanism. Solutions close to the CP conserving cases seem to be favored., 14 pages, 1 figure

The three flavor linear sigma model is studied as a ``toy model'' for understanding the role of possible light scalar mesons in the \pi \pi, \pi K and \pi \eta scattering channels. The approach involves computing the tree level partial wave amplitude for each channel and unitarizing by a simple K-matrix prescription which does not introduce any new parameters. If the renormalizable version of the model is used there is only one free parameter. While this highly constrained version has the right general structure to explain \pi \pi scatteirng, it is ``not quite'' right. A reasonable fit can be made if the renormalizability (for the {\it effective} Lagrangian) is relaxed while chiral symmetry is maintained. The occurence of a Ramsauer Townsend mechanism for the f_0(980) region naturally emerges. The effect of unitarization is very important and leads to ``physical'' masses for the scalar nonet all less than about 1 GeV. The a_0(1450) and K_0^*(1430) appear to be ``outsiders'' in this picture and to require additional fields. Comparison is made with a scattering treatment using a more general non-linear sigma model approach. In addition some speculative remarks and a highly simplified larger toy model are devoted to the question of the quark substructure of the light scalar mesons., Comment: Submitted to Phys. Rev. D. 45 pages, 12 figures

We study $\ensuremath{\pi}\ensuremath{\eta}$ scattering in a model which starts from the tree diagrams of a non-linear chiral Lagrangian including appropriate resonances. Previously, models of this type were applied to $\ensuremath{\pi}\ensuremath{\pi}$ and $\ensuremath{\pi}K$ scattering and were seen to require the existence of light scalar $\ensuremath{\sigma}(560)$ and $\ensuremath{\kappa}(900)$ mesons and to be consistent with the ${f}_{0}(980).$ The present calculation extends this to include the ${a}_{0}(980),$ thereby completing a possible nonet of light scalars, all ``seen'' in the same manner. We note that, at the initial level, the $\ensuremath{\pi}\ensuremath{\eta}$ channel is considerably cleaner than the $\ensuremath{\pi}\ensuremath{\pi}$ and $\ensuremath{\pi}K$ channels for the study of light scalars. This is because the large competing effects of vector meson exchange and ``current-algebra'' contact terms are absent. The simplicity of this channel enables us to demonstrate the closeness of our exactly crossing symmetric amplitude to a related exactly unitary amplitude. The calculation is also extended to higher energies in order to let us discuss the role played by the ${a}_{0}(1450)$ resonance.

We study the chiral phase transition for vectorlike $\mathrm{SU}(N)$ gauge theories as a function of the number of quark flavors ${N}_{f}$ by making use of an anomaly-induced effective potential. We modify an effective potential of a previous work, suggested for ${N}_{f}lN,$ and apply it to larger values of ${N}_{f}$ where the phase transition is expected to occur. The new effective potential depends explicitly on the full $\ensuremath{\beta}$ function and the anomalous dimension $\ensuremath{\gamma}$ of the quark mass operator. By using this potential we argue that chiral symmetry is restored for $\ensuremath{\gamma}l1.$ A perturbative computation of $\ensuremath{\gamma}$ then leads to an estimate of the critical value ${N}_{f}^{c}$ for the transition.

We study the ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ decay within an effective chiral Lagrangian approach in which the lowest lying scalar meson candidates $\ensuremath{\sigma}(560)$ and $\ensuremath{\kappa}(900)$ together with the ${f}_{0}(980)$ and ${a}_{0}(980)$ are combined into a possible nonet. We show that there exists a unique choice of the free parameters of this model which, in addition to fitting the $\ensuremath{\pi}\ensuremath{\pi}$ and $\ensuremath{\pi}K$ scattering amplitudes, well describes the experimental measurements for the partial decay width of ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ and the energy dependence of this decay. As a by-product, we estimate the ${a}_{0}(980)$ width to be 70 MeV, in agreement with a new experimental analysis.