Matthias Jamin

Strangeness-changing scalar form factors

Abstract We derive expressions for strangeness-changing scalar form factors, which incorporate known theoretical constraints both at low and high energies. Their leading behaviour in the limit of a large number of colours is calculated from the resonance chiral Lagrangian, and a set of short-distance constraints on the scalar resonance couplings is obtained, imposing the form factors to vanish at infinite momentum transfer. The important effects of meson rescattering are taken into account by exploiting unitarity and analyticity. Making use of previous results on S-wave Kπ scattering [1] , and a coupled-channel dispersion-relation analysis, the Kπ , Kη and Kη ′ scalar form factors are calculated up to 2xa0GeV. These scalar form factors are a key ingredient in the determination of the corresponding scalar spectral function which is important in the extraction of the mass of the strange quark from QCD sum rules as well as hadronic τ decays.

S-wave Kπ scattering in chiral perturbation theory with resonances

Abstract We present a detailed analysis of S-wave Kπ scattering up to 2 GeV, making use of the resonance chiral Lagrangian predictions together with a suitable unitarisation method. Our approach incorporates known theoretical constraints at low and high energies. The present experimental status, with partly conflicting data from different experiments, is discussed. Our analysis allows to resolve some experimental ambiguities, but better data are needed in order to determine the cross-section in the higher-energy range. Our best fits are used to determine the masses and widths of the relevant scalar resonances in this energy region.

V(us) and m(s) from hadronic tau decays.

Recent experimental results on hadronic tau decays into strange particles by the OPAL Collaboration are employed to determine V(us) and m(s) from moments of the invariant mass distribution. Our results are V(us)=0.2208+/-0.0034 and m(s)(2 GeV)=81+/-22 MeV. The error on V(us) is dominated by experiment and should be improvable in the future. Nevertheless, already now our result is competitive with the standard extraction of V(us) from K(e3) decays, and it is compatible with unitarity.

Baryon masses and flavour symmetry breaking of chiral condensates

Abstract The masses of the baryon octet and decuplet are reproduced with a (10–20)% accuracy by ratios of exponential moment QCD spectral sum rules, obeying the τ (sum rule variable) stability criterion. The onset of the QCD continuum is determined by consistency with the lowest dimensional finite energy sum rule. The N-Δ mass splitting is mainly controlled by the size of the mixed 〈 ψ σGψ〉 condensate. The observed masses of the strange baryons can only be reproduced if there is a large breaking of the chiral condensates 〈 ψ ψ〉 and 〈 ψ σGψ〉. This result is independent of the choice of the nucleon current.

Flavour-symmetry breaking of the quark condensate and chiral corrections to the Gell-Mann–Oakes–Renner relation

Abstract The relation between the chiral quark condensate in QCD sum rules and chiral perturbation theory is clarified with the help of a low-energy theorem for the scalar and pseudoscalar correlation functions. It is found that the quark condensate should be identified with the non-normal-ordered vacuum expectation value of quark–antiquark fields. Utilising results on flavour SU(3) breaking of the quark condensate from QCD sum rules, the low-energy constant H 2 r in the chiral Lagrangian, as well as next-to-leading order corrections to the Gell-Mann–Oakes–Renner relation are estimated.

Light quark masses from scalar sum rules

Abstract. In this work, the mass of the strange quark is calculated from QCD sum rules for the divergence of the strangeness-changing vector current. The phenomenological scalar spectral function which enters the sum rule is determined from our previous work on strangeness-changing scalar form factors [1]. For the running strange mass in the

f(B) and f(B(s)) from QCD sum rules

bar{rm MS}

A 1996 analysis of the CP violating ratio ε′/ε☆

scheme, we find

Order p 6 chiral couplings from the scalar Kπ form factor

m_s(2 {mathrm{GeV}})=99pm 16 {mathrm{MeV}}

Diquarks, {QCD} Sum Rules and Weak Decays

. Making use of this result and the light quark mass ratios obtained from chiral perturbation theory, we are also able to extract the masses of the lighter quarks