QUANTUM SYMMETRIES INDUCED BY PHONONS IN THE HUBBARD-MODEL

We show how the addition of a phonon field to the Hubbard model deform s the superconducting su(2) part of the global symmetry Lie algebra su (2) x su(2)/Z2, holding at half filling for the customary model, into a quantum [su(2)]q, symmetry, holding for a filling which depends on t he electron-phonon interaction strength. Such symmetry originates in t he feature that in the presence of phonons the hopping amplitude turns out to depend on the coupling strength. The states generated by resor ting to this new q symmetry exhibit both off-diagonal long-range order and pairing.