We investigate few-boson systems with resonant interactions in a narrow harmonic trap within an effective theory framework. The size of the model space is identified with the effective theory cutoff. ...In the universal regime, the interactions of the bosons can be approximated by contact interactions. We investigate the convergence properties of genuine and smeared contact interactions as the size of the model space is increased and present a detailed error analysis. The spectra for few-boson systems with up to 6 identical particles are calculated by combining extrapolations in the cutoff and in the smearing parameter.
We show that instanton effects may play an important role in the decay of scalar mesons into two pseudoscalars. Particularly the branching ratios of two meson decays of the
f
0(1500), which is ...considered as a glue-ball candidate, are compatible with an ordinary
q
q
-structure of this resonance and a small positive SU(3) mixing angle, in agreement with a result from a recent calculation of the spectrum with the same instanton-induced force. Predictions for the
a
0(1450)-branching ratios are made.
Few-body systems with resonant short-range interactions display universal properties that do not depend on the details of their structure or their interactions at short distances. In the three-body ...system, these properties include the existence of a geometric spectrum of three-body Efimov states and a discrete scaling symmetry. Similar universal properties appear in 4-body and possibly higher-body systems as well. We set up an effective theory for few-body systems in a harmonic trap and study the modification of universal physics for 3- and 4-particle systems in external confinement. In particular, we focus on systems where the Efimov effect can occur and investigate the dependence of the 4-body spectrum on the experimental tuning parameters.
We present a Poincaré covariant calculation of the generalized parton distribution of the pion. Results for different values of the kinematical parameters are shown and discussed.
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