The (two-neutrino) double beta decay, the electron capture with positron emission and the double electron capture decay rates are estimated for several nuclides by assuming the dominance of the lowest 1+ state of the intermediate isobar. By using single-β decay matrix elements and energy denominators as experimental imputs we get values independently of nuclear physics calculations. The results for double β- decay are in agreement with the recent geochemical values. Other predictions are within the present experimental sensitivity
The rate of the decay K f +p+p+n-is computed in a relativistic quark model for the mesons. This double-beta decay is assumed to be induced by a light Majorana neutrino mass m,. The rate for this mode is 7X 10-19 sec-', for m,-1 keV.
The Hoft structure of the central extension of the U q sl (n) algebra is considered. The intertwine matrix induces new integrable spin chain models. We show the relation of these models and the biparametric spin chain sl p,q (n) models. The cases n = 2 are n = 3 are discussed and for n = 2 we obtain the model of Dasgupta and Chowdhury . The case n = 3 is solved with nested Bethe ansatz method and it is showed the dependence of the Bethe equations in the second parameter
The reflection equations in a su(3) spin chain with open boundary conditions are analyzed. We find non diagonal solutions to the boundary matrices. The corresponding hamiltonian is given. The solutions are generalized to su(n) .
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