  Phonon-induced spin relaxation rates in quantum dots are studied as function
of in-plane and perpendicular magnetic fields, temperature and electric field,
for different dot sizes. We consider Rashba and Dresselhaus spin-orbit mixing
in diferent materials, and show how Zeeman sublevels can relax via
piezoelectric and deformation potential coupling to acoustic phonons. We find
that strong lateral and vertical confinements may induce minima in the rates at
particular values of the magnetic field, where spin relaxation times can reach
even seconds. We obtain good agreement with experimental findings in GaAs
quantum dots.
