Pietro Castoldi

CENTRAL PSEUDOSCALAR PRODUCTION IN PP SCATTERING AND THE GLUON CONTRIBUTION TO THE PROTON SPIN

Abstract Central pseudoscalar production in pp scattering is suppressed at small values of Q⊥, where Q is defined as the difference between the momenta transferred from the two protons. Such a behaviour is expected if the production occurs through the fusion of two vectors. Photon exchange could provide the dominant contribution at low transferred momenta, but we argue that an extension of the experiment could probe the gluon contribution to the proton spin.

Strong coupling limit of gφ4 theory: General formalism and applications

Abstract A method, independently proposed by Kaiser and by us, to study the strong coupling limit of the Green functions is described and discussed. Although its quantum mechanical version exhibits unusual features, an application to the anharmonic oscillator indicates that the method is able to reproduce correctly known numerical results. In spite of difficulties in the setting up of a renormalization program for the theory, a preliminary study of the CS β function for the gφ4 interaction shows that β(g r is asymptotically linear in the renormalization coupling constant. Evidence is given for the compatibility of this behaviour with the information that can be drawn from the known perturbative expansion.

Strong coupling limit of the gφ4 theory

Abstract The strong coupling limit of the gφ4 theory in the framework of the path integral formalism. An expansion of the Greens functions in negative powers of the coupling constant is obtained; at each order the dependence on the external momenta is of polynomial type. A renormalization procedure is proposed; the asymptotic behaviour of the Callan-Symanzik β function is studied and the existence of a stable ultraviolet fixed point is established.

Sur la formulation de modèles de l'amplitude de diffusion élastique à partir de la méthode ND-1

Abstract The ND −1 equations for the elastic scattering of two identical particles without spin are written under the hypothesis that the partial wave amplitude satisfies a dispersion relation with one subtraction. The N and D functions satisfy a set of two coupled singular integral equations and depend on the left hand discontinuity and on the inelasticity factor. These quantities are the basic parameters for model theories, and if they satisfy suitable asymptotic conditions, the solution of the ND −1 equations exists and is unique. The asymptotic behaviour of the real part of the phase shift is studied and gives a possible generalization of Levinsons theorem. Some simple models are examined, which illustrate various points of the method.

Determination of the low energy pion-pion scattering

The dispersion relation for forward π±π0 elastic scattering is solved by imposing consistency in the low-energy region between input cross section and output cross section. The I = 2, S-partial wave amplitude has a scattering length a2 ap; 0.26 and vanishes at ω ap; 457 MeV. The model proposed by Wanders and collaborators is used to test this behavior: no serious incompatibility with the conditions of Martin is found if the I = 0. S-partial wave amplitude has a scattering length a0 ap; 0.8 and vanishes at s ap; −2.4.

η′→ π+ π− π0: a key to understanding the η−η′ system

Different approaches to the description of the process η′ηππ can be clearly distinguished by the experimental determination of the slope of the Dalitz plot for η′→ π0π+π−.

Pion production in some neutrino-induced reactions

Abstract A recent application of soft-pion techniques to the study of pion production in neutrino-induced reactions is examined and discussed. An alternative approach, also based on PCAC and current algebra, is proposed and approximate results concerning the production, not necessarily at rest, of a physical pion are derived.

Calculation of the mass and width of Y

Abstract A self-consistent calculation of the mass and coupling constants of the Y∗ (1.385 MeV) has been performed. The (πΛ), (πΣ), ( K N ) coupled channels are taken into account. Writing the amplitude matrix in the form ND−1, approximate calculations are given of the Nij(s) functions which are represented as pole terms; they depend on the parameters of the Y∗. A self- consistent technique is employed; the calculated mass and decay widths are m( Y ∗ )≈1.365 MeV , Γ( Y ∗ →πΛ)≈40 MeV ; Γ( Y ∗ →πΣ)≈3 MeV .