The enhancement ∆Γ(Λb) of the Λb decay rate due to four-fermion processes of weak scattering and Pauli interference is calculated within the quark model. An estimate of the relative bu wave function at zero separation, |Ψ(0)|bu, is obtained in terms of the Σ ∗ b − Σb hyperfine splitting, the B∗ − B hyperfine splitting, and the B meson decay constant fB. For M(Σ∗b)−M(Σb) = 56±16 MeV,M(B ∗)−M(B) ...

4 M. Petrillo, P. Cherubini, G. Fravolini, M. Marchetti, J. Ascher, M. Schärer, H.-A. Synal, D. 5 Bertoldi, F. Camin, R. Larcher, and M. Egli 6 7 Department of Geography, University of Zurich, 8057 Zurich, Switzerland 8 WSL Swiss Federal Institute for Forest, Snow and Landscape Research, 8903 Birmensdorf, 9 Switzerland 10 Laboratory of Ion Beam Physics, ETH Zurich, 8093 Zurich, Switzerland 11 D...

The transition from instanton-dominated quantum tunneling regime to sphaleron-dominated classical crossover regime is explored in (1+1)dimensional scalar field theory when spatial coordinate is compactified. It is shown that the type of sphaleron transition is critically dependent on the circumference of the spatial coordinate.

In recent studies it has become increasingly clear that presence of infinitely many instability bands of the parametric resonance plays crucial roles in the phenomenon of particle production under periodic classical field oscillation. We extend previous works to a general class of models including both the Yukawa and the quartic type of couplings of the classical field to quantum bose fields. D...

Positronium, the bound state of an electron and positron, is an excellent laboratory to test our understanding of Quantum Electrodynamics of bound states. Although in the majority of cases the agreement between theory and experiment is very good, the case of orthopositronium (o-Ps) decay into three photons is outstanding, since the theoretical predictions differ by about 6 standard deviations f...

We investigate a relationship between the number of the negative modes around periodic instanton solution and the type of the decay-rate transition. It is shown that for the case of first-order decay-rate transition the lowest positive mode at low energy periodic instanton becomes additional negative mode at high energy regime, while in the second-order case there is only one negative mode in t...