Angular momentum and quantum spin

[touqra]

Is there an invariance relation for angular momentum similar to $$E^2 = p^2 + m^2$$ ?
How about quantum spin ?

 

[pam]

Nothing simple. rXp is a combination of three components of two four vectors.
It can be transformed but the result is complicated.
Quantum spin can be transformed using the Dirac equation, but it too is complicated except for special cases.