SCALAR NONETS IN POLE-DOMINATED QCD SUM RULES

The light scalar nonets are studied using the QCD sum rules for the tetraquark operators. The operator product expansion for the correlators is calculated up to dimension 12 and this enables us to perform analyses retaining sufficient pole-dominance. To classify the light scalar nonets, we investigate the dependence on current quark mass and flavor dynamics. Especially, to examine the latter, we study separately SU(3) singlet and octet states, and show that the number of annihilation diagrams is largely responsible for their differences, which is also the case even after the inclusion of the finite quark mass. Our results support the tetraquark picture for isosinglets, while that for octets is not conclusive yet.

FLAVOR-SPIN SYMMETRY AND THE TENSOR CHARGE

Exploiting an approximate phenomenological symmetry of the JPC = 1+- light axial vector mesons and using pole dominance, we calculate the flavor contributions to the nucleon tensor charge. The result depends on the decay constants of the axial vector mesons and their couplings to the nucleons.

NONLEPTONIC DECAYS OF B MESONS AND STRONG COUPLING CONSTANTS

Nonleptonic decays of B mesons into two mesons or meson resonances are studied on the basis of two versions of simple pole dominance models involving scalar, vector, pseudoscalar and axial vector poles. The results are compared with those obtained from the usual factorization model and are used to obtain information on strong coupling constants between the B meson and one light or one charmed meson, respectively. These coupling constants are compared to results from various QCD sum rule calculations.

Form Factors for Exclusive Semileptonic B Decays

We investigate the form factors for exclusive semileptonic decays of B meson to D, D*, based on the parton picture and helped by the results of the HQET. We obtain the numerical results for the slope of the Isgur–Wise function, which is consistent with the experimental results, and we extract the dependence of hadronic form factors on q2 by varying the input heavy quark fragmentation function without the nearest pole dominance ansätze.

q2-Dependence of Heavy-to-Light Transitions

The q2-dependence of the heavy-to-light form factors in the full physical region is obtained within the relativistic quark model with heavy infrapropagators. It is shown that the behavior of the vector form factors agrees with the pole dominance hypothesis whereas the behavior of the axial form factors is rather different from the polelike function.

Root Locus Diagrams and the Effect of Zeros on System Response

New expressions, and a graphical notation are introduced to quantify the effect of zeros on step response characteristics. The expressions, which also hold for non-minimum phase systems, are illustrated geometrically in the s-plane, and give a more accurate insight into a concept of pole dominance than the standard ‘pure-pole’ approximations.