M. G. Olsson

The nucleon sigma term from threshold parameters

Abstract A new sum rule determines the nucleon sigma term by the πN elastic scattering threshold parameters alone. This “threshold” value of σ (2 μ 2 ) provides an independent check of existing values obtained from global dispersive analyses, and also provides a realistic error assignment. Employing a recent analysis of low energy ( T π πN data our sum rule implies σ (2 μ 2 )=71±9 MeV.

Universal behavior in excited heavy-light and light-light mesons

A common pattern of large orbital and radial excitations in heavy-light and light-light mesons is demonstrated. For a general potential model with linear confinement the Regge slopes of the light degrees of freedom for these mesons are shown to be in the ratio of 2. The possibility of `tower` degeneracy occurs only with pure scalar confinement. {copyright} {ital 1997} {ital The American Physical Society}

Analytic quantization of the QCD string

We perform an analytic semi-classical quantization of the straight QCD string with one end fixed and a massless quark on the other, in the limits of orbital and radial dominant motion. We compare our results to the exact numerical semi-classical quantization. We observe that the numerical semi-classical quantization agrees well with our exact numerical canonical quantization.

Radiative rare B decays revisited

We reexamine contributions of higher K-resonances to the radiative rare decays b → sγ in the limit where both the b- and s-quark are considered heavy. Using form factor definitions consistent with the HQET covariant trace formalism, we find significant disagreement with previous work and excellent agreement with experimental results. In particular, the two largest fractions of the inclusive b → sγ branching ratio are found to be (16.8 |+- 6.4)% for B → K∗ (892)γ and (6.2 ± 2.9)% for B → K2∗ (1430)γ decays. We also compare the contribution from the radiative decays into the eight K-meson states to the inclusive experimental b → sγ mass distribution.

Reduction of the QCD string to a time component vector potential

We demonstrate the equivalence of the relativistic flux tube model of mesons to a simple potential model in the regime of large radial excitation. We make no restriction on the quark masses; either quark may have a zero or finite mass. Our primary result shows that for fixed angular momentum and large radial excitation, the flux tube or QCD string meson with a short-range Coulomb interaction is described by a spinless Salpeter equation with a time component vector potential

From scalar to string confinement

V(r)=ar\ensuremath{-}k/r.

Instantaneous Bethe-Salpeter equation

We outline a connection between scalar quark confinement, a phenomenologically successful concept heretofore lacking fundamental justification, and QCD. Although scalar confinement does not follow from QCD, there is an interesting and close relationship between them. We develop a simple model intermediate between scalar confinement and the QCD string for illustrative purposes. Finally, we find analytically the bound state spectrum of the light degrees of freedom for a spinless, massless quark in scalar, time-component vector, and string confinement through semi-classical quantization.

Semileptonic form factors: A model-independent approach

Abstract We present an analysis which uses Regge structure and the Bjorken and Voloshin HQET sum rules to restrict the choice of parameters of a relativistic quark model.

Modelling form factors in HQET

We present a systematic algebraic and numerical investigation of the instantaneous Beth-Salpeter equation. Emphasis is placed on confining interaction kernels of the Lorentz scalar, time component vector, and full vector-types. We explore the stability of the solutions and Regge behavior for each of these interactions, and conclude that only time component vector confinement leads to normal Regge structure and stable solutions for all quark masses.