  All Lie symmetries of the Burgers equation driven by an external random force
are found. Besides the generalized Galilean transformations, this equation is
also invariant under the time reparametrizations. It is shown that the Gaussian
distribution of a pumping force is not invariant under the symmetries and
breaks them down leading to the nontrivial vacuum (instanton). Integration over
the volume of the symmetry groups provides the description of fluctuations
around the instanton and leads to an exactly solvable quantum mechanical
problem.
