  We describe the mechanism of charge-spin transformation in a double quantum
dot (DQD) with even occupation, where a time dependent gate voltage v(t) is
applied to one of its two valleys, whereas the other one is coupled to the
source and drain electrodes. The Kondo tunneling regime under strong Coulomb
blockade may be realized when the spin spectrum of the DQD is formed by the
ground state spin triplet and two singlet excitations. Charge fluctuations
induced by v(t) result in transitions within the spin multiplet characterized
by the SO(5) dynamical symmetry group. In a weakly non-adiabatic regime the
decoherence, dephasing and relaxation processes affect Kondo tunneling. Each of
these processes is caused by a special type of dynamical gauge fluctuations, so
that one may discriminate between the decoherence in the ground state of a DQD
and dephasing at finite temperatures.
