Francesco Sannino

Simple description of {pi}{pi} scattering to 1 GeV

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.

Exploring pi pi scattering in the 1/N(c) picture

In the large

Generalization of the Bound State Model

{\mathit{N}}_{\mathit{c}}

Toy model for breaking super gauge theories at the effective Lagrangian level

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/

Hidden Structure in a Lagrangian for Hyperfine Splitting of the Heavy Baryons

{\mathit{N}}_{\mathit{c}}

Hyperfine splitting of low-lying heavy baryons

expansion, but may nevertheless be important. The latter two flavor model gives a reasonable description of the phase shift

Scaling behavior in soliton models

{\mathrm{\ensuremath{\delta}}}_{0}^{0}

Violation of the ΔI = 12 rule in D → ππ decays☆

up until around 860 MeV, before the effects associated with the KK\ifmmode\bar\else\textasciimacron\fi{} threshold come into play.

Violation Of The

In the bound state approach the heavy baryons are constructed by binding, with any orbital angular momentum, the heavy meson multiplet to the nucleon considered as a soliton in an effective meson theory. We point out that this picture misses an entire family of states, labeled by a different angular momentum quantum number, which are expected to exist according to the geometry of the three-body constituent quark model (for N{sub C}=3). To solve this problem we propose that the bound state model be generalized to include orbitally excited heavy mesons bound to the nucleon. In this approach the missing angular momentum is {open_quotes}locked up{close_quotes} in the excited heavy mesons. In the simplest dynamical realization of the picture we give conditions on a set of coupling constants for the binding of the missing heavy baryons of arbitrary spin. The simplifications made include working in the large M limit, neglecting nucleon recoil corrections, neglecting mass differences among different heavy spin multiplets, and also neglecting the effects of light vector mesons. {copyright} {ital 1997} {ital The American Physical Society}

\Delta I = 1/2

We propose a toy model to illustrate how the effective Lagrangian for super QCD might go over to the one for ordinary QCD by a mechanism whereby the gluinos and squarks in the fundamental theory decouple below a given supersymmetry breaking scale m. The implementation of this approach involves a suitable choice of possible supersymmetry breaking terms. An amusing feature of the model is the emergence of the ordinary QCD degrees of freedom which were hidden in the auxiliary fields of the supersymmetric effective Lagrangian.