Testing for new physics in singly Cabibbo suppressed D decays

We devise tests for a new physics origin of the recently measured direct CP violation in singly Cabibbo-suppressed D decays. The tests take the form of sum rules for the CP asymmetries in various D decays. They are based on the fact that within the standard model CP violation arises from interference of the dominant tree amplitudes with the Delta I = 1/2 penguin amplitudes. The sum rules would be violated if the observed CP violation is due to new physics contributions to the effective weak Hamiltonian that change the isospin by Delta I =3/2.