a) Write down all possible parity and time-reversal invariant terms with no derivatives that are bilinear in the nucleon field N and that have one factor of the quark mass matrix M.
b) Reexpress your result in terms of the nucleon field N.
c) Use the observed neutron-proton mass difference, mn−mp=1.293MeV, and the mu/md ratio you found in problem 83.6, to determine as much as you can about the coefficients of the terms you wrote down. (Ignore the mass difference due to electromagnetism.)