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J. Schechter

Publications and source records attributed to J. Schechter.

29 records · Page 2Linked to original sources
arXiv1996

Scaling Behavior in Soliton Models

In the framework of chiral soliton models we study the behavior of static nucleon properties under rescaling of the parameters describing the effective meson theory. In particular we investigate the question of whether the Brown--Rho scaling laws are general features of such models. When going beyond the simple Skyrme model we find that restrictive constraints need to be imposed on the mesonic parameters in order to maintain these scaling laws. Furthermore, in the case when vector mesons are included in the model it turns out that the isoscalar form factor no longer scales according to these laws. Finally we note that, in addition to the exact scaling laws of the model, one may construct approximate {\it local scaling laws}, which depend of the particular choice of Lagrangian parameters.

nucl-th↗
arXiv1995

Heavy Quark Solitons: Towards Realistic Masses

A generalization of the effective meson Lagrangian possessing the heavy quark symmetry to finite meson masses is employed to study the meson mass dependence of the spectrum of S-- and P wave baryons containing one heavy quark or anti-quark. These baryons are described as respectively heavy mesons or anti-mesons bound in the background of a soliton, which is constructed from light mesons. No further approximation is made to solve the bound state equation. For special cases it is shown that the boundary conditions, which have to be satisfied by the bound state wave--functions and stem from the interaction with the light mesons, may impose additional constraints on the existence of bound states when finite masses are assumed. Two types of models supporting soliton solutions for the light mesons are considered: the Skyrme model of pseudoscalars only as well as an extension containing also light vector mesons. It is shown that only the Skyrme model with vector mesons provides a reasonable description of both light and heavy baryons. Kinematical corrections to the bound state equations are included in the discussion.

hep-ph↗
arXiv1995

Resolving Ordering Ambiguities in the Collective Quantization by Particle Conjugation Constraints

We formulate the particle conjugation operation and its convenient realization as $G$--parity in the framework of several chiral soliton models. The Skyrme model, the Skyrme model with vector mesons and the chiral quark model are specifically treated. The vector and axial vector currents are classified according to their behavior under $G$--parity. In the soliton sector particle conjugation constrains {\it a priori} ambiguous orderings of operators in the space of the collective coordinates. In the Skyrme model with vector mesons and in a local chiral model with an explicit valence quark this classification scheme provides consistency conditions for the ordering of the collective operators appearing in the $1/N_C$ corrections to the nucleon axial charge and the isovector magnetic moment. These consistency conditions cause the corrections obtained from an ordinary perturbation expansion to vanish in the context of the collective quantization of the static soliton configuration. This conclusion presumably applies to all local effective chiral models.

hep-ph↗
arXiv1995

Exploring $\pp$ scattering in the $\1N$ picture

In the large $N_c$ approximation to $QCD$, the leading $\pp$ 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 one $GeV$ 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 $ρ$ meson in a chirally invariant manner substantially delays the onset of drastic unitarity violation which would be present for the {\it 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 $\1N$ expansion, but may nevertheless be important. The latter two flavor model gives a reasonable description of the phase shift $δ^0_0$ up until around $860 MeV$, before the effects associated which the $K\bar{K}$ threshold come into play.

hep-ph↗
arXiv1994

Particle Conjugation and the $1/N_C$ Corrections to $g_A$

We impose the requirement that the isovector axial vector current for the soliton sector of the chiral quark model transforms correctly under particle conjugation. This forces us to choose an otherwise arbitrary ordering of collective space operators in such a way that the next--to--leading $1/N_C$ correction to $g_A$ vanishes.

hep-ph↗
arXiv1994

Possible Extension of the Chiral Perturbation Theory Program

After a brief discussion of how chiral dynamics has evolved from the ``universal V-A theory of weak interactions'', we present some evidence that symmetry breaking for the vector meson multiplet is not simpler than but rather analogous to that for the pseudoscalar multiplet. This provides a motivation for speculating on how to extend in a systematic way the chiral perturbation theory program to include vectors.

hep-ph↗
arXiv1993

Heavy Quark Solitons

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.

hep-ph↗
arXiv1992

Symmetry Breaking in a Generalized Skyrme Model

We first outline the calculations of the neutron-proton mass difference and of the axial singlet matrix element (relevant to the "proton spin" puzzle) in a generalized Skyrme model of pseudoscalars and vectors. These two calculations are, perhaps surprisingly, linked to each other and furthermore are sensitive to some fine details of symmetry breaking in the effective meson Lagrangian. This provides a motivation for us to examine these symmetry breaking terms more closely. We find a qualitatively new feature in the symmetry breaking pattern of the vector meson system and discuss its significance. (Talk at Workshop on "Baryons as Skyrme Solitons," Sept. 28-30, 1992, Siegen, Germany.)

hep-ph↗
arXiv1992

Effective Hadron Dynamics: From Meson Masses to the Proton Spin Puzzle

We construct a three flavor chiral Lagrangian of pseudoscalars and vectors with special emphasis on the symmetry breaking terms. Comparing tree level two and three point functions with experiment allows us to first, fix the parameters of the model (including the light quark mass ratios) and second, to predict $m(K^{*+})-m(K^{*\circ}),\, Γ(K^*\rightarrow Kπ)$ and $Γ(ϕ\rightarrow K {\overline K})$. The last mentioned quantities come out reasonably well, in contrast to an ``ordinary" $SU(3)$ treatment. For this purpose we need ``second order" symmetry breakers involving the vector fields analogous to those needed for the chiral perturbation theory program with only pseudoscalars. An improved description of the $η-η^\prime$ system is also given. We then use the soliton sector of this improved chiral Lagrangian to investigate some aspects of baryon physics which are especially sensitive to symmetry breaking. For this purpose a fairly elaborate ``cranking" techinque is employed in connection with the collective Hamiltonian. In addition to the ``strong" baryon mass spectrum a careful investigation is made of the non-electromagnetic part of the neutron-proton mass difference. This work is needed to improve our previous estimates concerning the two component approach to the ``proton spin" puzzle. We find that both the ``matter" and ``glue" contributions are small but they do tend to cancel each other.

hep-ph↗
arXiv1992

Role of Light Vector Mesons in the Heavy Particle Chiral Lagrangian

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.

hep-ph↗