Symmetry breaking: what is the subgroup left?

krishna mohan

Hi....

I have studied the standard model of particle physics and know that spontaneous symmetry breaking by a vev breaks SU(2)xU(1) to a U(1). How do we know to what group a vev will break the original group?

I have heard of Dynkin diagrams. Are they only for continuous groups? Is there any other method for discrete groups?

Any reference given will be appreciated.