Extended Time-Reversal Operator and the Symmetries of the Hyperon-Nucleon Interaction

Abstract

An extended time-reversal operator incorporating charge conjugation in the flavor SU3 space is introduced in order to study the spin-flavor structure of the hyperon-nucleon inter­ action. Particle-hole conjugation in terms of this extended time reversal is found to be useful to characterize time-reversal odd components for the space-spin part of the hyperon-nucleon interaction, which yield non-zero contributions to the exchange Feynman diagram or to the transition amplitude between AN and EN systems when the flavor symmetry breaking is properly introduced. Some selection rules are also given for the spin-flavor factors appearing in the quark-model potentials of the hyperon-nucleon interaction. Since quantum chromo dynamics (QCD) was found to be the fundamental the­ ory of the strong interaction, a number of models have been proposed to understand nucleon-nucleon (N N) and hyperon-nucleon (Y N) interactions from more basic ele­ ments of quarks and gluons. Among these models, the non-relativistic quark model is in a unique position to enable us to take full account of the dynamical motion of the two composite baryons, though it can only describe confinement using a phe­ nomenological potential and it employs the quark-quark (qq) residual interaction derived from the color analogue of the Fermi-Breit interaction. Thanks to this ad­ vantage it can give a realistic description of the N Nand Y N interaction, if the missing meson-exchange effect, which dominates at the long-range part of the in­ teraction, is properly taken into account. Since the quark model can describe the short-range part of the N Nand Y N interactions within the unified framework of the resonating-group method (RGM). the symmetry properties of these interactions in the spin-flavor SU6 space become among the most important issues determining the quality of the model. A simultaneous description of the N Nand Y N interactions has recently been