D. Tadić

Parity-violating nuclear interactions and models of the weak Hamiltonian

Abstract The derivation of the parity-violating internucleon one-meson-exchange potentials is presented, stressing their connection with models of the weak interactions. Relevant problems concerning second class currents, gauge invariance, off-mass-shell effects, symmetry breaking and multimeson exchanges are discussed. An extensive bibliography of existing literature is also presented.

Calculation of non-leptonic hyperon decay amplitudes without arbitrary parameters

Abstract Non-leptonic hyperon decay amplitudes are calculated starting from the Weinberg-Salam model and employing the QCD renormalized effective weak Hamiltonian which includes the effects of SU(4) symmetry breaking. The amplitudes are described through the commutator approximation (s-wave), the ground-state pole approximation (p-wave) and separable contributions. Values of all parameters are taken from either experiments or theoretical estimates. Such a no-parameter approach works well for s-wave amplitudes, reproducing their relative signs and absolute magnitudes. For p-wave amplitudes the relative signs are correctly reproduced, while some magnitudes are too small. The importance of separable contributions and of the so-called “penguin” terms is explicitly shown.

Weak meson decays and the 1Nc expansion

Abstract In the QCD corrected weak hamiltonian, the leading terms in the large- N c limit give a reasonable description of D→ K π decays and good values of K → ππ decay amplitudes.

KL − KS mass difference and quark models

Abstract The matrix element 〈 K 0 |H W | K 0 〉 is calculated in the quark MIT bag model and in several relativized versions of the quark harmonic-oscillator models for hadrons. The results of the MIT bag model depend strongly on the particular choice of parameters, while the results of the harmonic-oscillator model are relatively stable on the variation of model parameters. The harmonic-oscillator model which takes into account the c.m. motion (the RHO model) is in reasonably good agreement with the vacuum-saturation value.

Quark dynamics and the weak non-leptonic decays of K and D mesons

Abstract Quark model predictions for K → 2π and D → Kπ decays were investigated in dynamical frameworks based on the separable approximation (SA), current algebra (CA), current algebra modified for the meson moment dependence (CAC) and current algebra with final-state interactions (CAF). Relativistic and non-relativistic quark model predictions were compared. The effective weak hamiltonian was modified by changing the relative strengths of its flavour 20 and 84 parts. All these approaches were also applied to hyperon and Ω − non-leptonic decays. When using standard QCD enhancement, the best approximation for K → 2π (CAC) works poorly with D → Kπ. The best approximatiob for D→Kπ (CAF) fails in the case of K → 2π. Only CAC with the 84 piece of the hamiltonian quenched might be in agreement with studied weak decays.

QCD calculation of the parity-violating NNπ amplitude in the Weinberg-Salam model and flavor-symmetry breaking

A parity-violating ΔS = 0 effective weak Hamiltonian has been calculated from the Weinberg-Salam model by taking into account QCD corrections and by allowingfor SU(4) flavor symmetry breaking. Non-separable contributions to the parity-violating NNπ amplitude A(n−0 have been estimated in the framework of the MIT bag model. Separable contributions to this amplitude are mostly due to the operators which mix left and right quark helicities. Double breaking of isospin symmetry, included in the calculation of the separable contributions to hadronic matrix elements (so-called “penguin” diagrams), causes an enhancement in comparison with the “standard” value A(n−0 = 5 × 10−8. The Weinberg-Salam model values are likely to be in the region 25 × 10−8 ⩽ A(n−0) ⩽ 30 × 10−8. Experimental consequences are also discussed.

p-wave non-leptonic hyperon decay amplitudes and the positive-parity excited baryons

Abstract It is shown that 1 2 + resonance poles contribute significantly to the p-wave hyperon non-leptonic decay amplitudes. The calculation was carried out by using the QCD-corrected WS GIM weak hamiltonian and the Isgur-Karl description of the positive-parity baryons. The agreement with experiment is very much improved. This is achieved by using parameters either straight from experiment or from the Isgur-Karl harmonic oscillator model. That means that the expected accuracy of our calculations is of about 20% at best and that it should be smaller for the amplitudes found by subtracting large numbers.

Calculations of nonleptonic Ω− decay branching ratios

Abstract Nonleptonic Ω − decay branching ratios have been calculated using the Weinberg-Salam model with QCD corrections and the MIT bag model. The whole scheme is equivalent to that which works well for nonleptonic hyperon decays. The calculated values are in qualitative and even rough quantitative with experimental data.

Parity violation in proton-nucleon scattering at high-energy

Abstract The asymmetry a in proton-nucleon scattering at high energies is calculated. The weak Born one-boson exchange amplitudes are derived in the framework of the standard Salam-Weinberg model including QCD corrections. The distortion due to the strong interaction is included via a Glauber-type formalism that uses forward amplitudes obtained by a dispersion relation analysis which exploits all the available information on total cross sections in pure spin states. Our results for p-p scattering a pp are positive and of the order 10 −7 over the entire range of the lab momentum 1.3 GeV/ c ⩽ P l ⩽ 19 GeV/ c , while a pn is typically an order of magnitude smaller and of opposite sign. When compared with a recent experiment, at P l = GeV/ c and using water as a target, our result is smaller by almost two orders of magnitude. All the theoretical inputs of the calculation are discussed in detail and none by itself seems to be able to explain this large discrepancy.

Hard and Soft Gluonic Effects in Charmed Baryon Decays

AbstractThe QCD-enhanced effective weak hamiltonian for the Weinberg-Salam model including hardgluonic corrections is used to calculate the experimentally measured ratio